This work was funded by the call &#39;CO2-neutral fuels&#39; supported by Shell, the Foundation for Fundamental Research on Matter (FOM), and the Netherlands Organization for Scientific Research (NWO).&#160;The authors would like to thank Eddie van Veldhuizen, Ana Sobota and Sander Nijdam for allowing us to use their lab space and their generous support in general.

NOTE: For a schematic version of the setup, see Figure 2.
1. Microwave Plasma Experimental Layout
<ol>
	<li>Connect the 1 kW magnetron to the circulator with a water load attached.</li>
	<li>Connect the isolator to the three-stub tuner that is used for impedance matching of the waveguide to the plasma.</li>
	<li>Attach the applicator to the three-stub tuner and add a sliding short in the end of the waveguide.</li>
	<li>Place a 17 mm or 27 mm inner diameter quartz tube in the hole of the applicator. 
	NOTE: The microwaves are absorbed in a flowing CO2 gas that is contained in this tube.</li>
	<li>Complete the vacuum setup by connecting the quartz tube to the KF-flanges and a gas inlet.</li>
	<li>Use KF-16 for the 17-mm quartz tube and KF-40 for the 27-mm quartz tube. Use a tangential gas inlet to induce a vortex flow, which prevents the hot plasma from touching the walls.</li>
	<li>Connect a throttle valve in series with the vacuum pump; this allows for variation of the pressure from 5 mbar to atmospheric pressure by effectively regulating the pumping speed.</li>
	<li>In parallel to the throttle valve, connect a shortcut valve to switch between low pressure (required to facilitate ignition of the plasma) and high pressure without losing the pressure setting of the throttle valve.</li>
	<li>Connect a mass flow controller to the gas inlet so that the gas flow can be regulated between 0.5 and 10.0 SLM.</li>
	<li>Turn on the water cooling of the magnetron before starting the plasma.</li>
	<li>Make sure to enable safety systems, such as a radiation meter for monitoring stray microwave radiation and a gas-detector for monitoring ambient CO, H2 or NOx concentrations. These safety systems are essential during experiments.</li>
	<li>Turn on the power by manually turning up the power level of the source and increase to maximal power.</li>
	<li>Adjust the plunger by moving it back and forth slightly, while constantly monitoring if the reflected power is decreased. Aim to minimize the reflected power. Adjust the three-stub tuners by turning them until the reflected power is minimized. If a network analyzer is available, follow the procedure reported by Leinz10. 
	NOTE: The vacuum and microwave system can be seen in Figure 3A.</li>
</ol>
2. Optical Layout of the Rayleigh Scattering Diagnostic
<ol>
	<li>Align the 532 nm Nd:YAG laser beam with the use of mirrors such that it enters the setup axially. The laser has a 10 Hz repetition rate and a max power of 600 mJ per pulse.</li>
	<li>Mount windows on opposite sides (entrance and exit) of the reactor. Use windows that have been anti-reflection (AR) coated for 532 nm to prevent excessive stray light. Alternatively, use Brewster windows in combination with an external beam dump.</li>
	<li>Start the laser by following the user manual (see Table of Materials).</li>
	<li>Align the laser by using a low output power program. Start with a Q-switch delay of 0 &#181;s so that no light output is generated. Then increase the delay in steps of 5 &#181;s until the light output is visible.</li>
	<li>If the beam is too bright go down in steps of 1 &#181;s to achieve &#34;adequate&#34; brightness, i.e., the lowest power at which the beam spot is still visible.</li>
	<li>Mount a second AR-coated window at the laser beam exit side of the vacuum system, to dump the beam on an external beam-dump. Alternatively, instead of the window, mount a vacuum beam dump. A schematic version of the setup can be seen in Figure 2. 
	NOTE: The elimination of the window reduces the stray light in the plasma discharge regions, which is essential to achieve detectable Rayleigh scattering signal levels.</li>
	<li>Place a lens with a focal distance of 2.4 m in the beam path, just before the entrance window, to focus the laser to the center of the waveguide. The long focal distance reduces stray light in the Rayleigh scattering collection region. Place the lens as close as possible to the window to reduce the incident power density so that it remains below the damage threshold of the windows. 
	NOTE: Prevent laser breakdown in the gas, especially in the laser focus. After focusing the laser, flow CO2 in the reactor at a pressure above the pressures to be measured. If no laser breakdown can be observed, then it will not occur at the lower pressures and higher temperatures where measurements take place, because the species density will be much lower. If a loud crackling noise is heard accompanied by visible blue flashes, lower the laser power.</li>
	<li>Install regularly spaced baffles inside the vacuum tubes to further reduce the stray light levels in the plasma discharge region due to scattering at the entrance window11.</li>
	<li>Prepare a plunger with a 24-mm diameter aperture for optical access perpendicular to the laser beam. The limited aperture size prevents significant microwave radiation losses.</li>
</ol>
3. Optical Setup - Detection Branch
<ol>
	<li>Place a lens (f = 100 mm, 51 mm diameter) perpendicular to the reactor and collect the scattered light through the hole in the plunger as shown in Figure 3A. Focus the light onto a 400 &#181;m diameter optical fiber and position it in the lens image. 
	NOTE: The fibers are positioned in a linear array of 59 fused silica fibers with an input height of 26.7 mm and a length of 40 m.</li>
	<li>Use the fiber to guide the light to the spectrometer. 
	NOTE: Here the light is imaged onto the entrance slit with a width that is tunable down to 10 &#181;m. The magnification of the collection optics results in an axial detection range of approximately 20 mm. A spectrometer is used to filter out the coinciding C2 swan emission. If the experimenter is only interested in Rayleigh scattering, a suitable bandpass filter can also be used for this purpose. In that case, steps 3.3 to 3.6 can be skipped. The spectral filter could be eliminated altogether by comparing the measured light intensity with and without laser pulse, greatly simplifying the optical setup. If the monochromator is eliminated, it is not possible to extend the measurements to Thomson or Raman scattering, for which spectral resolution is needed.</li>
	<li>Use a spectrometer (in house constructed) to spectrally resolve the scattered light. 
	NOTE: As can be seen in Figure 2, the spectrometer consists of an entrance slit, steering mirror, Littrow lens, dispersive grating, image intensifier, focusing lenses, and CCD-camera.</li>
	<li>Inside the spectrometer, place a mirror to reflect the incoming light to the Littrow lens with a focal distance of 0.3 m and a diameter of 80 mm. 
	NOTE: The spectrometer is in the &#39;Littrow&#39; configuration, which means that incident and diffracted light have the same angle to the grating normal. Consequently, the same lens is used for collimating incoming light and imaging diffracted light onto the detector.</li>
	<li>Rotate the diffraction grating on a rotation stage to tune to the appropriate wavelength range. For a Nd:YAG laser, this is typically between 524 and 540 nm. The grating is 11 x 11 cm2 and has a groove density of 1,200 mm-1 that is optimized for first order diffraction. This results in a resolution of 0.027 nm/px. Figure 3B shows a picture of the grating and Littrow lens. 
	NOTE: The grating will image multiple spots as a result of higher order; make sure that only the 1st order maximum ends up on the image intensifier.</li>
	<li>Place two lenses to image the intensified light on a CCD-camera (Figure 3C).</li>
	<li>Quantify the stray light contributions. Pump down to a pressure of 60 mbar and measure the scattered intensity. Reduce the pressure and measure the intensity again. Repeat this until the pressure cannot be lowered any further.</li>
	<li>When plotting the intensity vs. pressure, ensure that there is a linear relationship. Extrapolate the linear function to zero pressure. 
	NOTE: Since no Rayleigh scattering can occur at zero pressure, the intensity at the intercept is the stray light level. The result of this procedure is shown in Figure 4.</li>
	<li>Adjust the gating parameters of the image intensifier to optimize the intensity recorded by the CCD. Start with a gate pulse that starts well before and ends well after the laser pulse so that the entire laser pulse is captured.</li>
	<li>Take into account the time-of-flight delay of the light because the light has to travel through the entire optical setup. Reduce the delay while making sure that the intensity is not reduced. 
	NOTE: A time window of 30 ns was found to be adequate for a 9 ns pulse. To increase the gain, increase the multichannel-plate voltage to the maximum voltage (here, 850 V). If the CCD-camera is over-exposed a smaller multichannel-plate voltage can be chosen.</li>
</ol>
4. FTIR Spectrometer
<ol>
	<li>Place an FTIR spectrometer in the exhaust of the gas, downstream of the plasma, to measure the CO-production rate. Place the spectrometer far enough from the reactor to ensure the gas is in chemical equilibrium. In the setup described, the distance from the plasma was 2 m.</li>
	<li>Put a cell in the sample compartment of the FTIR spectrometer with in- and outlet bellows connected in series with the vacuum system. This is shown schematically in Figure 5.</li>
	<li>Mount a CaF2 window on each side of the cell to allow the IR-beam to probe the gas.</li>
	<li>Change the signal gain until the signal intensity is as close as possible to the maximum, but not exceeding it. The maximum allowable intensity may be different from device to device.</li>
	<li>Click on the &#39;interferogram&#39; preview. An interferogram is now visible, with a high peak in the center and a low intensity at the shoulders.</li>
	<li>Before starting measurements, measure a background at vacuum (&#60; 0.1 mbar). To do this make sure that the reactor is at vacuum and there is no gas flow; then record a background by clicking &#39;Background&#39; in the &#39;Signal Level Monitor&#39; window.</li>
	<li>Turn on the microwave by increasing the power to maximum, until the plasma ignites. The pressure used for plasma ignition is ~ 1 mbar.</li>
	<li>Record a spectrum in the range from 2,400 to 2,000 cm-1; this includes the CO and main CO2 band.</li>
	<li>Average the spectra to reduce noise; a value of 10&#160;averages was used in this experiment. Fit the measured CO-lines using the HITRAN-database12. 
	NOTE: This results in a CO volume fraction. The pressure is measured and used as an input parameter to find the total number density. The temperature is assumed to be room temperature, which is justified by the distribution of rovibrational peaks in the spectrum.</li>
	<li>For measuring in situ spectra, place the reactor inside the sample compartment as depicted in Figure 6 and 7.</li>
	<li>Switch to a sapphire instead of quartz tube to enable radial measurements. The sapphire transmits IR-light down to 1,800 cm-1.</li>
	<li>With in situ measurements, use a high number of averages of at least 100 to average out fluctuations in the plasma.</li>
	<li>Decorate the compartment walls with microwave absorbent material to reduce the stray microwave radiation (Eccosorb OCF was used here).</li>
	<li>Take care that the interferogram does not saturate as a result of the additional IR-emission by the plasma. If this is the case, change the DC-offset of the detector. Correct the resulting spectra for the temperature dependent absorption of sapphire13.</li>
	<li>If an IR-camera is used for measuring the temperature, use a camera that is sensitive in a range for which the sapphire is not transparent, i.e. higher than 6 &#181;m, so that the tube temperature rather than the plasma is measured. 
	NOTE: Recommended values for the absorption of sapphire as a function of temperature can be found in14.</li>
</ol>

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A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plasma-chemical+process+of+CO2+dissociation+in+a+nonequilibrium+microwave+discharge.">Plasma-chemical process of CO2 dissociation in a nonequilibrium microwave discharge.</a> Zh Tek Fiz. 51, 925-931 (1981).</li><li>Will, S., Schraml, S., Leipertz, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-dimensional+soot-particle+sizing+by+time-resolved+laser-induced+incandescence.">Two-dimensional soot-particle sizing by time-resolved laser-induced incandescence.</a> Opt Lett. 20, 2342-2344 (1995).</li><li>Lepoutre, F., Louis, G., Manceau, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Collisional+relaxation+in+CO2+between+180+K+and+400+K+measured+by+the+spectrophone+method.">Collisional relaxation in CO2 between 180 K and 400 K measured by the spectrophone method.</a> Chem Phys Lett. 48, 509-514 (1977).</li></ol>

The authors declare that they have no competing financial interests.

Both for the electrification of the chemical industry and mitigating the intermittency in renewable energy, continuous flow reactors are needed for driving chemistry in a sustainable system. It has been recognized that continuous flow reactors will play an important role in revolutionizing the chemical industry21. More specifically, the plasma reactor has been identified as a commercially attractive alternative to chemical plants in the production of CO2 neutral fuels due to their simplicity, compactness and low price22. A wide range of plasma technologies have been proposed for the dissociation of CO223, including Corona discharges24,25,26, nanosecond pulsed discharges27, micro hollow cathode discharges28, microplasmas29, dielectric barrier discharges30,31,32,33, gliding arcs34,35, and microwave plasmas37,38. Out of these vastly varying technologies, the microwave plasma and gliding arc have been operated with the highest power, in the kW range, and have shown the best efficiencies, 40% for a gliding arc and 60-80% for a microwave discharge. Both the microwave plasma and the gliding arc reactor can be run at high power, a necessary condition for scaling up to ~ 100 kW, which is projected for a practical application. The operation of the microwave plasma is not limited to CO2 dissociation and might also be used for methane reforming and nitrogen fixation. The main drawback of the microwave reactor is the low pressure (100 mbar) in optimal conditions, which limits the maximal gas throughput.
The described procedure was demonstrated with CO2, but it can be used without alteration for activation of CH4, N2 or other stable molecules. In most of these cases, different IR-bands need to be measured that correspond to the expected products like NH3, NOx, C2H2, C2H4, etc. Running methane plasma can be cumbersome as the soot - one of the reaction products - is deposited to the walls and will absorb microwaves, effectively extinguishing the plasma. Although vibrational pumping is much less effective in methane than in CO2 because of the high VT-transfer rates, plasma-catalysis can nevertheless be advantageous for methane (Fridman5, p.688)
Accurate Rayleigh scattering measurements are difficult to achieve in a soot-forming plasma, because of the high stray light contribution as a result of Mie scattering on the soot particles. Although it complicates the Rayleigh measurements, it could be used to quantify the density of soot particles instead39. Raman scattering could provide an attractive alternative for measuring temperature in this environment, as it allows for spectrally distinguishing the stray light and (Raman) scattered light components. The integration time of the Raman scattering is in the order of ~ 20 minutes, so that the fluctuations in the plasma are averaged out. Only long term effects like heating of the system could affect the measurement, as it slightly increases the pressure in the reactor.
Precisely because of the large spectral overlap between stray light and Rayleigh scattered light, the importance of stray light suppression (even in the absence of soot) cannot be overstated. The stray light can be reduced by properly placing baffles, increasing the focal distance of the laser and setup length, and increasing the tube diameter. The use of a vacuum beam dump further reduces the stray light levels as it eliminates the exit window. Alternatively, Brewster windows can be used as well. As described before, some knowledge of the composition is required (either measured or simulated) to properly account for the different Rayleigh cross sections.
The flowing microwave plasma has proven itself to be a viable method of driving chemistry with an energy efficiency of up to 50%, the flexibility of fast switching, and using only inexpensive materials. The recorded temperatures in the center however, are much higher than what is favorable for high vibrational overpopulation. By reducing the temperature, even higher energy efficiencies can be reached. Although lowering the power (e.g., to 200 W) would lower the gas temperature, without additional optimization of the reactor, it also lowers the efficiency.
Two other ways of reducing the temperature are suggested here. The first way is to pulse the microwave power. By applying the power in pulses shorter rather than the typical VT-relaxation time, the gas can cool down in between the pulses and as a result, less power is lost in the VT-relaxation. This in turn means more power is invested in the vibrational pumping that promotes efficient dissociation. The VT-relaxation time is 70 &#181;s at room temperature and 100 mbar40, which serves as an upper limit for the pulse ON-time. Pulsing can only increase efficiency in a plasma regime where the main conversion pathway is by non-equilibrium conversion. The second way to increase efficiency is to add alkali impurities to tailor the EEDF8. By controlling the EEDF, and in particular the electron temperature, the electrons can more efficiently transfer their energy to molecular vibrations, which again results in the promotion of higher vibrational levels that are essential to highly efficient reactions.

This paper describes a protocol for a flowing microwave plasma of up to 1 kW, while measuring the plasma gas temperature and CO2 conversion.
Concerns for climate change and the consequent awareness for sustainability have driven a steady growth of the global share of renewable energy. However, the intermittent nature of solar and wind energy places stress on the energy system and inhibits further increasing deployments. Storage (long and short term) and conversion (e.g., into chemical fuels) are required to mitigate intermittency and to make sustainable energy available to other sectors such as transportation. The CO that is produced in the reactor can be used as feedstock gas for the synthesis of e.g., methane or liquid fuels. By using these to fuel power plants, electricity can be generated even when the instantaneous production of renewable energy is low. The CO2 that is produced in these plants forms a closed loop so that no net CO2 is introduced in the atmosphere, making it a clean cycle.
The system can only mitigate the intermittency if the switching time is smaller than the fluctuations in the energy supply. In the present configuration, the startup time is determined by the need to start under ideal breakdown conditions and then tune to optimal conversion conditions. In principle, this can be overcome by ignition with other means like a focused laser or spark. Plasma physics limitations are on the order of 0.1 ms. This is much shorter than the timescale of typical atmospheric effects, like e.g., clouds moving over a solar panel array. Extrapolating from the current system to a real application in a sustainable fuel production setting is still a rather long shot. Ideally, there would be a series of microwave reactors of 100-500 kW, each connected to a solar panel field or wind turbine, with switching of the individual reactors according to the energy supply.
This paper discusses a plasma approach, generically suitable for the application of conversion/activation of stable molecules such as CO2, N2 and CH4. Here, it is introduced through the specific example of reduction of CO2 to CO as a first step in chemical fuel synthesis. The flowing microwave plasma reactor is suitable for solving intermittency problems as it has low startup times and can be built using inexpensive materials.
In microwave plasmas, the free plasma electrons move with the oscillating electric field of the microwaves. Energy is subsequently transferred to the heavy particles (neutral and ionized gas species) via collisions. Because of their large difference in mass, this reactor is mainly efficient in inelastic collisions. Firstly, there is ionization. In steady state, the ionization rate essentially equals losses due to recombination. However, as shown in Table 1, the ionization energies are in general significantly higher than the dissociation energies, which makes dissociation via ionization inherently inefficient. Likewise, the electron impact dissociation involves an energy threshold of more than 10 eV1and is also inherently inefficient. The reason that the plasma phase can still be an efficient mechanism to achieve molecular dissociation is the efficient excitation of vibrational modes2.
At the mean electron energies of a few eV that are common for the microwave plasma3, vibrational excitation is the dominant energy transfer pathway. The asymmetric stretch is particularly important because it can rapidly distribute energy among higher levels through intermolecular collisions. The energy exchange rate increases with temperature and decreases for larger&#916;E, and is large due to the anharmonicity in the vibrational ladder and the associated small energy difference in two adjacent vibrational modes4. The up-pumping of higher vibrational levels can go all the way up to dissociation, which results in an energy efficient dissociation reaction5.
The high vibrational pumping in CO2 leads to a situation where higher vibrational modes are much more populated than they would be in a thermal equilibrium, ultimately producing the so-called Treanor distribution6. The condition for achieving overpopulation of the higher vibrational levels is that the Vibration-Vibration (V-V) relaxation rates are much higher than Vibration-Translation (V-T) relaxation rates. This is the case for the asymmetric stretch mode of CO2. The V-V relaxation rates decrease with increasing gas temperature, while the V-T rates increase. Since the V-T relaxations increase the gas temperature, a positive feedback mechanism can produce a runaway V-T relaxation, leading to the destruction of the overpopulation of higher vibrational levels. In other words, low gas temperatures are favorable for a strongly non-thermal distribution.
In effect, the plasma will exhibit distinctly different temperatures for the different species and their degrees of freedom. At the typical electron temperatures of a few eV, vibrational temperatures will be several thousands of degrees Celsius whilst the translational (gas) temperatures may remain below one thousand degrees Celsius. Such a situation is denoted as strong non-equilibrium and has been recognized to be favorable for chemical reactions.
The translational gas temperature, since it is so important for the energy efficiency at which the plasma might drive chemical reactions, demands accurate and spatially resolved diagnostics. Emission spectroscopy is the baseline approach in plasma physics to deduce temperatures. For example, it is possible to evaluate rotational spectra using impurities for optimal diagnosis. However, this always involves line of sight integration and therefore averaging. As we will see in the present paper, temperature gradients must be steep given the high central temperatures of up to ~ 4,000 K and edge temperatures determined by the wall of ~ 500 K. Under such circumstances, localized measurements are invaluable.
In the present work, local density measurements from Rayleigh Scattering are combined with pressure measurements to infer the temperature via the ideal gas law. The Rayleigh scattering measurements involve focusing a high-power laser in a sample volume from which the elastic scattering of the photons on the bound electrons of the CO2 molecules is detected. The gas temperature is related to the intensity of the Rayleigh signal via:
<img alt="Equation 1" src="/files/ftp_upload/55066/55066eq1.jpg" />
Here T is the gas temperature, p is the pressure measured by a pressure gauge, I is the measured Rayleigh intensity, d&#963;/d&#937;(T) is the Rayleigh cross section and C is a calibration constant. Since the cross section d&#963;/d&#937;(T) is species dependent we see that for high temperatures, where dissociation is significant, the calibration constant is a function of temperature. It is assumed that in the hot center, only equilibrium conversion takes place, so that the species concentration for a given temperature can be calculated. In this way, one can numerically calculate the effective cross section for a given temperature, which is used to calculate the Rayleigh intensity that is expected to be measured for a range of temperatures7. This effective cross section as a function of temperature is shown in Figure 1.
The performance of the plasma conversion is quantified by the means of FTIR. It is assumed in the present case of CO2 reduction that the net reaction in the plasma is:
<img alt="Equation 2" src="/files/ftp_upload/55066/55066eq2.jpg" />
This allows the use of a single conversion factor &#945;, which is related to the CO volume fraction by
<img alt="Equation 3" src="/files/ftp_upload/55066/55066eq3.jpg" />,
which follows from the concentrations that are inferred from the spectral signatures of CO and CO2 in the FTIR-spectra. We note that the effective Rayleigh cross section cannot easily be deduced from the overall conversion factor as determined by FTIR. The overall conversion is not only set by the central reactor temperature but also by the subtleties in the actual radial profile of the gas temperature.
The present paper details our proposed diagnostic scheme for the characterization of microwave plasma chemical gas conversion and illustrates its faculty with selected examples. Full parameter scans in terms of gas flow, pressure and microwave power for the reactor under evaluation can be found in7,8,9.

<table border="0" cellpadding="0" cellspacing="0" width="893">
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		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">1kW magnetron</td>
			<td style="width:255px;">Muegge</td>
			<td style="width:215px;">MW-GIRYJ1540-1K2-08</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Circulator with water load</td>
			<td style="width:255px;">Philips</td>
			<td style="width:215px;">2722 163 02101</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">3-stub tuner</td>
			<td style="width:255px;">IBF-electronic</td>
			<td style="width:215px;">WR340PTUN3AC174A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Applicator with sliding short</td>
			<td style="width:255px;">homemade</td>
			<td style="width:215px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">17mm ID / 20 mm OD Quartz tube</td>
			<td style="width:255px;">Saillart</td>
			<td style="width:215px;">custom</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">27mm ID / 30 mm OD Quartz tube</td>
			<td style="width:255px;">Saillart</td>
			<td style="width:215px;">custom</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">18mm ID / 20 mm OD Sapphire tube</td>
			<td style="width:255px;">Precision Sapphire Technologies</td>
			<td style="width:215px;">custom</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">KF-vacuum flanges</td>
			<td style="width:255px;">Hositrad</td>
			<td style="width:215px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Mass flow controller</td>
			<td style="width:255px;">Tylan/Brooks</td>
			<td style="width:215px;">FC-2901V-4V</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">MFC control unit</td>
			<td style="width:255px;">MKS</td>
			<td style="width:215px;">PR-3000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Pressure guage</td>
			<td style="width:255px;">Edwards</td>
			<td style="width:215px;">ASG-2000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Vacuum pump</td>
			<td style="width:255px;">Edwards</td>
			<td style="width:215px;">E2M18</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Nd:YAG laser</td>
			<td style="width:255px;">Continuum</td>
			<td>Powerlite DLS 8000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">AR-coated window</td>
			<td style="width:255px;">Eksma Optics</td>
			<td>210-1202E + 3025-i0 (coating)</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Diffraction grating</td>
			<td style="width:255px;">Jobin Yvon</td>
			<td style="width:215px;">520-25-120</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Image Intensifier</td>
			<td style="width:255px;">Katod</td>
			<td style="width:215px;">EPM102G-04-22S</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Intensifier power source</td>
			<td style="width:255px;">homemade</td>
			<td style="width:215px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Spectrometer lens 1</td>
			<td style="width:255px;">Nikon</td>
			<td style="width:215px;">135mm f/2 DC</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">Spectrometer lens 2</td>
			<td style="width:255px;">Nikon</td>
			<td style="width:215px;">AF-S 85 mm f/1.8g</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">CCD-camera</td>
			<td style="width:255px;">Allied Optics</td>
			<td style="width:215px;">Manta G-145B</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">FTIR-spectrometer (exhaust)</td>
			<td style="width:255px;">Varian/Agilent</td>
			<td style="width:215px;">Cary 670</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">FTIR-spectrometer (in-situ)</td>
			<td style="width:255px;">Bruker</td>
			<td style="width:215px;">Vertex 80v</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:259px;">CaF2 windows</td>
			<td style="width:255px;">Crystran</td>
			<td>CAFP25-2U</td>
			<td></td>
		</tr>
	</tbody>
</table>

non-equilibrium microwave plasma for efficient high temperature chemistry

A flowing microwave plasma based methodology for converting electric energy into internal and/or translational modes of stable molecules with the purpose of efficiently driving non-equilibrium chemistry is discussed. The advantage of a flowing plasma reactor is that continuous chemical processes can be driven with the flexibility of startup times in the seconds timescale. The plasma approach is generically suitable for conversion/activation of stable molecules such as CO2, N2 and CH4. Here the reduction of CO2 to CO is used as a model system: the complementary diagnostics illustrate how a baseline thermodynamic equilibrium conversion can be exceeded by the intrinsic non-equilibrium from high vibrational excitation. Laser (Rayleigh) scattering is used to measure the reactor temperature and Fourier Transform Infrared Spectroscopy (FTIR) to characterize in situ internal (vibrational) excitation as well as the effluent composition to monitor conversion and selectivity.

In this section, representative results for the flowing plasma reactor are presented. It is found that the CO-conversion is shown to increase linearly with specific energy, until about 2.2 eV/molecule. The energy efficiency &#951; is calculated as:
<img alt="Equation 4" src="/files/ftp_upload/55066/55066eq4.jpg" />
Here &#945; is the measured conversion, q the molecular gas flow rate, &#916;E = 2.7 eV the net dissociation energy, and Pin the input power. By using the measured conversion (explained in next paragraph), we can find the energy efficiency of the plasma reactor, which is plotted for a variety of pressures and powers and a fixed flow rate of 13 SLM in Figure 8A and 8B. The plasma proved capable of converting CO2 to CO with an energy efficiency of up to 49%, which is comparable to the maximal thermodynamic efficiency5. Although the efficiency reported here is close to that of thermal dissociation, it proves that a non-equilibrium plasma can produce a higher CO volume fraction than in equilibrium at the measured translational temperature.A great advantage over thermal dissociation is that the reaction can be turned on or off in a few seconds, which is needed for mitigating fluctuating power production. In addition, there is the potential to increase the efficiency further by tailoring the Electron Energy Distribution Function (EEDF).
We now focus on results obtained for the exhaust. The CO-concentration is measured by IR absorption spectroscopy. In Figure 9A and 9B, a representative spectrum is shown. The fit results in a temperature of 299.36 K and a conversion of 14.7%. The measured data (blue) is in good comparison with the fit data (green). Since the temperature in the exhaust is close to room temperature, it is feasible to leave the temperature as a fixed parameter in the fitting procedure. Next, the in situ measurements are discussed. When interpreting the Rayleigh light intensity, it must be taken into account that the Rayleigh cross sections of the reaction products - CO, O and O2 - differ significantly from that of CO215,16. This issue can only be solved if information of the sample volume composition is available. If the Raman spectrum can be recorded, it is suggested to monitor the Raman spectrum of the CO-molecule to estimate the local number density of the products. A polarizer could be used in this case to eliminate stray light, Thomson, and Rayleigh scattering, while reducing the intensity of the rotational Raman scattered light by only a factor 3/717. If the Raman spectrum cannot be measured because the Rayleigh peak is not sufficiently reduced, the conversion can be estimated based on equilibrium conversion (see references7,20). Though this ignores the enhanced production due to non-equilibrium conditions, the gas temperatures are high enough to justify this simplification. In Figure 10, the temperature data are shown with the different Rayleigh cross sections included. It was found that without any optimization to the plasma, the gas in the plasma center can reach temperatures of up to 5,000 K. It has been shown in Ar plasmas that the Thomson scattering and scattering from excited species becomes significant if the temperature reaches the order of 10,000 K 18,19,20, making the temperature measurement unreliable. Given the values of the differential cross sections for Rayleigh and Thomson scattering of 0.148&#183;10-30 m2 and 7.94&#183;10-30 m2, respectively, an ionization degree of 1.9&#183;10-4 would be necessary for a Thomson contribution of 1%. This is much higher than the ionization degree predicted to be present in the plasma (Fridman5, p294) of 1&#183;10-6 to 8&#183;10-5.
The in situ FTIR-measurements were at a flow of 2.0 slm and a significantly lower pressure of 5 mbar to make a homogeneous plasma, which ensures a reliable path-integrated measurement. This also means that the plasma itself touches and heats the wall. To prevent the wall from becoming too hot, the power is reduced to only 30 W. Although CO-production is negligible at this low power and pressure, the in situ FTIR still provides relevant insights into the dynamics of the CO2 plasma. Spectra were recorded with a resolution of 0.125 cm-1. The spectrum was fitted with a model based on HAPI, the application programming interface of HITRAN12. The code was modified to include separate temperatures for the different vibrational normal modes. A single temperature T12 was used for both the symmetric stretch and bending mode, because the Fermi-resonance guarantees a rapid relaxation between the two normal modes.
The result of the fit is T = 700 K, T12 = 1,250 K, and T3 = 1,500 K, as shown in Figure 11. The fitted pressure was 10 mbar. This overestimation is likely to compensate for an underestimated temperature coefficient for the pressure broadening constants. The gas temperature found with Rayleigh scattering can differ from the one found with FTIR, since Rayleigh scattering measures local temperatures while the FTIR spectra are line integrated.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/55066/55066fig1.jpg" /> 
Figure 1: Temperature dependence of Rayleigh cross section 
The Rayleigh cross section that results when from the different cross sections for reaction products. A conversion in the thermal equilibrium is assumed to calculate the relative species mole fractions. <a href="https://cloudflare.jove.com/files/ftp_upload/55066/55066fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/55066/55066fig2.jpg" /> 
Figure 2: Optical setup for Rayleigh measurements 
A lens focuses the laser light to the quartz tube center. The waveguide launches microwaves into the plasma, positioned in the focus of the laser. A hole in the plunger provides optical access for the laser chord. The spectrometer consists of (1) the entrance slit, (2) a steering mirror, (3) the Littrow lens, (4) dispersive grating, (5) image intensifier, (6) and (7) focusing lenses, and (8) CCD-camera. <a href="https://cloudflare.jove.com/files/ftp_upload/55066/55066fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/55066/55066fig3.jpg" /> 
Figure 3: Pictures of setup 
(A) Picture of the vacuum setup, including the microwave applicator and optical fibers. (B) Picture of the inside of the spectrometer, with the Littrow lens and diffraction grating visible. (C) Picture of the lens system used to image the intensified light to the CCD-camera. <a href="https://cloudflare.jove.com/files/ftp_upload/55066/55066fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/55066/55066fig4.jpg" /> 
Figure 4: Measured intensity as function of pressure 
The measured Rayleigh scattering as a function of pressure, for different points in time. The blue solid line represents a linear fit of the data. The error bars indicate the absolute error of the pressure gauge. <a href="https://cloudflare.jove.com/files/ftp_upload/55066/55066fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/55066/55066fig5.jpg" /> 
Figure 5: Schematic drawing of FTIR gas exhaust analysis setup 
A gas cell is placed in the sample compartment of the FTIR spectrometer. The cell is connected in series with the exhaust so that gas is flowing through it. <a href="https://cloudflare.jove.com/files/ftp_upload/55066/55066fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/55066/55066fig6.jpg" /> 
Figure 6: In situ FTIR setup 
Schematic pictures of the in situ FTIR setup. The flow tube is upright and gas flows from the bottom to top. The tube is in the focus of the FTIR beam. <a href="https://cloudflare.jove.com/files/ftp_upload/55066/55066fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/55066/55066fig7.jpg" /> 
Figure 7: Pictures of the in situ FTIR setup 
Side (A) and top (B) view of the waveguide in the sample compartment of the FTIR-spectrometer. The bellows on the top of the waveguide are connected to the vacuum pump and act as an exhaust for the reactor. <a href="https://cloudflare.jove.com/files/ftp_upload/55066/55066fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/55066/55066fig8.jpg" /> 
Figure 8: Representative energy efficiency and conversion efficiency 
In graph (A), the energy efficiency for a typical plasma is depicted as a function of applied microwave power, at pressures ranging from 127 to 279 mbar. In graph (B), the conversion efficiency is depicted. <a href="https://cloudflare.jove.com/files/ftp_upload/55066/55066fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/55066/55066fig9.jpg" /> 
Figure 9: Representative infrared (IR) absorption spectrum of CO 
Graph (A) shows the measured IR absorption spectrum of the gas exhaust (blue dots). The green solid line shows the is least squares fit to the data. The fit results are T = 299.36 K and &#945; = 14.7%. A zoomed-in picture is shown in (B). <a href="https://cloudflare.jove.com/files/ftp_upload/55066/55066fig9large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/55066/55066fig10.jpg" /> 
Figure 10: Measured gas temperature 
In this graph, the gas temperature of the plasma center as measured by Rayleigh scattering is shown as a function of energy input for different pressures. <a href="https://cloudflare.jove.com/files/ftp_upload/55066/55066fig10large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 11" class="xfigimg" src="/files/ftp_upload/55066/55066fig11.jpg" /> 
Figure 11: In situ IR absorption spectrum of the plasma discharge 
Graph (A) shows the measured IR absorption spectrum of the CO2 discharge. The blue line gives the best fit to the data (green points) with T = 700 K, T12 = 1,250 K, and T3 = 1,500 K. The red line gives the residue of the fit. A zoomed in picture can be seen in (B). <a href="https://cloudflare.jove.com/files/ftp_upload/55066/55066fig11large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table fo:keep-together.within-page="1">
	<tbody>
		<tr>
			<td></td>
			<td>Ionization</td>
			<td>Dissociation</td>
		</tr>
		<tr>
			<td></td>
			<td>eV</td>
			<td>eV</td>
		</tr>
		<tr>
			<td>CO2</td>
			<td>13.77</td>
			<td>5.52</td>
		</tr>
		<tr>
			<td>CO</td>
			<td>14.01</td>
			<td>11.16</td>
		</tr>
		<tr>
			<td>O2</td>
			<td>12.07</td>
			<td>5.17</td>
		</tr>
		<tr>
			<td>N2</td>
			<td>15.58</td>
			<td>9.8</td>
		</tr>
		<tr>
			<td>CH4</td>
			<td>12.51</td>
			<td>4.54</td>
		</tr>
		<tr>
			<td>CH3</td>
			<td>9.84</td>
			<td>4.82</td>
		</tr>
		<tr>
			<td>CH2</td>
			<td>10.4</td>
			<td>4.37</td>
		</tr>
		<tr>
			<td>CH</td>
			<td>10.64</td>
			<td>3.51</td>
		</tr>
		<tr>
			<td>H2</td>
			<td>15.43</td>
			<td>4.52</td>
		</tr>
	</tbody>
</table>
Table 1: Ionization and dissociation energies of common species and products.

Watch this Scientific Journal Video about Non-equilibrium Microwave Plasma for Efficient High Temperature Chemistry at JoVE.com

Non-equilibrium Microwave Plasma for Efficient High Temperature Chemistry

This article describes a flowing microwave reactor that is used to drive efficient non-equilibrium chemistry for the application of conversion/activation of stable molecules such as CO2, N2 and CH4. The goal of the procedure described here is to measure the in situ gas temperature and gas conversion.

A flowing microwave plasma based methodology for converting electric energy into internal and/or translational modes of stable molecules with the purpose ...

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12.5K Views.  Dutch Institute for Fundamental Energy Research. This article describes a flowing microwave reactor that is used to drive efficient non-equilibrium chemistry for the application of conversion/activation of stable molecules such as CO2, N2 and CH4. The goal of the procedure described here is to measure the in situ gas temperature and gas conversion. 

Video: Non-equilibrium Microwave Plasma for Efficient High Temperature Chemistry

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes

Functionalized naphthalenes have applications in a variety of research fields ranging from the synthesis of natural or biologically active molecules to the preparation of new organic dyes. Although numerous strategies have been reported to access naphthalene scaffolds, many procedures still present limitations in terms of incorporating functionality, which in turn narrows the range of available substrates. The development of versatile methods for direct access to substituted naphthalenes is therefore highly desirable.
The Diels-Alder (DA) cycloaddition reaction is a powerful and attractive method for the formation of saturated and unsaturated ring systems from readily available starting materials. A new microwave-assisted intramolecular dehydrogenative DA reaction of styrenyl derivatives described herein generates a variety of functionalized cyclopenta[b]naphthalenes that could not be prepared using existing synthetic methods. When compared to conventional heating, microwave irradiation accelerates reaction rates, enhances yields, and limits the formation of undesired byproducts.
The utility of this protocol is further demonstrated by the conversion of a DA cycloadduct into a novel solvatochromic fluorescent dye via a Buchwald-Hartwig palladium-catalyzed cross-coupling reaction. Fluorescence spectroscopy, as an informative and sensitive analytical technique, plays a key role in research fields including environmental science, medicine, pharmacology, and cellular biology. Access to a variety of new organic fluorophores provided by the microwave-assisted dehydrogenative DA reaction allows for further advancement in these fields.

Microwave-assisted intramolecular dehydrogenative Diels-Alder (DA) reactions provide concise access to functionalized cyclopenta[b]naphthalene building blocks. The utility of this methodology is demonstrated by one-step conversion of the dehydrogenative DA cycloadducts into novel solvatochromic fluorescent dyes via Buchwald-Hartwig palladium-catalyzed cross-coupling reactions.

Functionalized naphthalenes have applications in a variety of research fields ranging from the synthesis of natural or biologically active molecules to ...

Preparation of Silica Nanoparticles Through Microwave-assisted Acid-catalysis

Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle diameters ranging from 30-250 nm by varying the reaction conditions. Through the selection of a microwave compatible solvent, silicic acid precursor, catalyst, and microwave irradiation time, these microwave-assisted methods were capable of overcoming the previously reported shortcomings associated with synthesis of silica nanoparticles using microwave reactors. The siloxane precursor was hydrolyzed using the acid catalyst, HCl. Acetone, a low-tan &#948; solvent, mediates the condensation reactions and has minimal interaction with the electromagnetic field. Condensation reactions begin when the silicic acid precursor couples with the microwave radiation, leading to silica nanoparticle sol formation. The silica nanoparticles were characterized by dynamic light scattering data and scanning electron microscopy, which show the materials&#39; morphology and size to be dependent on the reaction conditions. Microwave-assisted reactions produce silica nanoparticles with roughened textured surfaces that are atypical for silica sols produced by St&#246;ber&#39;s methods, which have smooth surfaces.

Silica nanoparticles were prepared using acid-catalysis of a siloxane precursor and microwave-assisted synthetic techniques resulting in the controlled growth of nanomaterials ranging from 30-250 nm in diameter. The growth dynamics can be controlled by varying the initial silicic acid concentration, time of the reaction, and temperature of reaction.

Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle ...

Quantitative Detection of Trace Explosive Vapors by Programmed Temperature Desorption Gas Chromatography-Electron Capture Detector

The direct liquid deposition of solution standards onto sorbent-filled thermal desorption tubes is used for the quantitative analysis of trace explosive vapor samples. The direct liquid deposition method yields a higher fidelity between the analysis of vapor samples and the analysis of solution standards than using separate injection methods for vapors and solutions, i.e., samples collected on vapor collection tubes and standards prepared in solution vials. Additionally, the method can account for instrumentation losses, which makes it ideal for minimizing variability and quantitative trace chemical detection. Gas chromatography with an electron capture detector is an instrumentation configuration sensitive to nitro-energetics, such as TNT and RDX, due to their relatively high electron affinity. However, vapor quantitation of these compounds is difficult without viable vapor standards. Thus, we eliminate the requirement for vapor standards by combining the sensitivity of the instrumentation with a direct liquid deposition protocol to analyze trace explosive vapor samples.

Trace explosive vapors of TNT and RDX collected on sorbent-filled thermal desorption tubes were analyzed using a programmed temperature desorption system coupled to GC with an electron capture detector. The instrumental analysis is combined with direct liquid deposition method to reduce sample variability and account for instrumentation drift and losses.

The direct liquid deposition of solution standards onto sorbent-filled thermal desorption tubes is used for the quantitative analysis of trace explosive ...

Metal-silicate Partitioning at High Pressure and Temperature: Experimental Methods and a Protocol to Suppress Highly Siderophile Element Inclusions

Estimates of the primitive upper mantle (PUM) composition reveal a depletion in many of the siderophile (iron-loving) elements, thought to result from their extraction to the core during terrestrial accretion. Experiments to investigate the partitioning of these elements between metal and silicate melts suggest that the PUM composition is best matched if metal-silicate equilibrium occurred at high pressures and temperatures, in a deep magma ocean environment. The behavior of the most highly siderophile elements (HSEs) during this process however, has remained enigmatic. Silicate run-products from HSE solubility experiments are commonly contaminated by dispersed metal inclusions that hinder the measurement of element concentrations in the melt. The resulting uncertainty over the true solubility and metal-silicate partitioning of these elements has made it difficult to predict their expected depletion in PUM. Recently, several studies have employed changes to the experimental design used for high pressure and temperature solubility experiments in order to suppress the formation of metal inclusions. The addition of Au (Re, Os, Ir, Ru experiments) or elemental Si (Pt experiments) to the sample acts to alter either the geometry or rate of sample reduction respectively, in order to avoid transient metal oversaturation of the silicate melt. This contribution outlines procedures for using the piston-cylinder and multi-anvil apparatus to conduct solubility and metal-silicate partitioning experiments respectively. A protocol is also described for the synthesis of uncontaminated run-products from HSE solubility experiments in which the oxygen fugacity is similar to that during terrestrial core-formation. Time-resolved LA-ICP-MS spectra are presented as evidence for the absence of metal-inclusions in run-products from earlier studies, and also confirm that the technique may be extended to investigate Ru. Examples are also given of how these data may be applied.

We present a procedure to determine the metal-silicate partitioning of siderophile elements, emphasizing techniques that suppress the formation of metal inclusions in experiments for the noble metals. The results of these experiments are used to demonstrate the effect of core-formation on the highly siderophile element composition of the mantle.

Estimates of the primitive upper mantle (PUM) composition reveal a depletion in many of the siderophile (iron-loving) elements, thought to result from ...

One-pot Microwave-assisted Conversion of Anomeric Nitrate-esters to Trichloroacetimidates

The goal of the following procedure is to provide a demonstration of the one-pot conversion of a 2-azido-1-nitrate-ester to a trichloroacetimidate glycosyl donor. Following azido-nitration of a glycal, the product 2-azido-1-nitrate ester can be hydrolyzed under microwave-assisted irradiation. This transformation is usually achieved using strongly nucleophilic reagents and extended reaction times. Microwave irradiation induces hydrolysis, in the absence of reagents, with short reaction times. Following denitration, the intermediate anomeric alcohol is converted, in the same pot, to the corresponding 2-azido-1-trichloroacetimidate.

A 2-azido-1-nitrate-ester can be converted to the corresponding 2-azido-1-trichloroacetimidate in a one-pot procedure. The goal of the manuscript is to demonstrate utility of the microwave reactor in carbohydrate synthesis.

The goal of the following procedure is to provide a demonstration of the one-pot conversion of a 2-azido-1-nitrate-ester to a trichloroacetimidate ...

Combustion Chemistry of Fuels: Quantitative Speciation Data Obtained from an Atmospheric High-temperature Flow Reactor with Coupled Molecular-beam Mass Spectrometer

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This flexible tool offers a detailed observation of chemical gas-phase kinetics in reacting flows under well-controlled conditions. The vast range of operating conditions available in a laminar flow reactor enables access to extraordinary combustion applications that are typically not achievable by flame experiments. These include rich conditions at high temperatures relevant for gasification processes, the peroxy chemistry governing the low temperature oxidation regime or investigations of complex technical fuels. The presented setup allows measurements of quantitative speciation data for reaction model validation of combustion, gasification and pyrolysis processes, while enabling a systematic general understanding of the reaction chemistry. Validation of kinetic reaction models is generally performed by investigating combustion processes of pure compounds. The flow reactor has been enhanced to be suitable for technical fuels (e.g. multi-component mixtures like Jet A-1) to allow for phenomenological analysis of occurring combustion intermediates like soot precursors or pollutants. The controlled and comparable boundary conditions provided by the experimental design allow for predictions of pollutant formation tendencies. Cold reactants are fed premixed into the reactor that are highly diluted (in around 99 vol% in Ar) in order to suppress self-sustaining combustion reactions. The laminar flowing reactant mixture passes through a known temperature field, while the gas composition is determined at the reactors exhaust as a function of the oven temperature. The flow reactor is operated at atmospheric pressures with temperatures up to 1,800 K. The measurements themselves are performed by decreasing the temperature monotonically at a rate of -200 K/h. With the sensitive MBMS technique, detailed speciation data is acquired and quantified for almost all chemical species in the reactive process, including radical species.

An investigation of the oxidative combustion chemistry of novel biofuels, fuel components, or jet fuels by comparison of quantitative speciation data is presented. The data can be used for kinetic model validation and enables fuel assessment strategies.This manuscript describes the atmospheric high-temperature flow reactor and demonstrates its capabilities.

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This ...

Synthesis of Soft Polysiloxane-urea Elastomers for Intraocular Lens Application

This study discusses a synthesis route for soft polysiloxane-based urea (PSU) elastomers for their applications as accommodating intraocular lenses (a-IOLs). Aminopropyl-terminated polydimethylsiloxanes (PDMS) were previously prepared via the ring-chain equilibration of the cyclic siloxane octamethylcyclotetrasiloxane (D4) and 1,3-bis(3-aminopropyl)-tetramethyldisiloxane (APTMDS). Phenyl groups were introduced into the siloxane backbone via the copolymerization of D4 and 2,4,6,8-tetramethyl-2,4,6,8-tetraphenyl-cyclotetrasiloxane (D4Me,Ph). These polydimethyl-methyl-phenyl-siloxane-block copolymers were synthesized for increasing the refractive indices of polysiloxanes. For applications as an a-IOL, the refractive index of the polysiloxanes must be equivalent to that of a young human eye lens. The polysiloxane molecular weight is controlled by the ratio of the cyclic siloxane to the endblocker APTMDS. The transparency of the PSU elastomers is examined by the transmittance measurement of films between 200 and 750 nm, using a UV-Vis spectrophotometer. Transmittance values at 750 nm (upper end of the visible spectrum) are plotted against the PDMS molecular weight, and &#62; 90% of the transmittance is observed until a molecular weight of 18,000 g&#183;mol&#8722;1. Mechanical properties of the PSU elastomers are investigated using stress-strain tests on die-cut dog-bone-shaped specimens. For evaluating mechanical stability, mechanical hysteresis is measured by repeatedly stretching (10x) the specimens to 5% and 100% elongation. Hysteresis considerably decreases with the increase in the PDMS molecular weight. In vitro cytotoxicity of some selected PSU elastomers is evaluated using an MTS cell viability assay. The methods described herein permit the synthesis of a soft, transparent, and noncytotoxic PSU elastomer with a refractive index approximately equal to that of a young human eye lens.

This study describes synthetic routes for aminopropyl-terminated polydimethylsiloxanes and polydimethyl-methyl-phenyl-siloxane-block copolymers and for soft polysiloxane-based urea (PSU) elastomers. It presents the application of PSUs as accommodating an intraocular lens. An evaluation method for in vitro cytotoxicity is also described.

This study discusses a synthesis route for soft polysiloxane-based urea (PSU) elastomers for their applications as accommodating intraocular lenses ...

Reducing Willow Wood Fuel Emission by Low Temperature Microwave Assisted Hydrothermal Carbonization

Biomass is a sustainable fuel, as its CO2 emissions are reintegrated in biomass growth. However, the inorganic precursors in the biomass cause a negative environmental impact and slag formation. The selected short rotation coppice (SRC) willow wood has a high ash content (<img alt="Equation 1" src="/files/ftp_upload/58970/58970eq1.jpg" /> = 1.96%) and, therefore, a high content of emission and slag precursors. Therefore, the reduction of minerals from SRC willow wood by low temperature microwave assisted hydrothermal carbonization (MAHC) at 150 &#176;C, 170 &#176;C, and 185 &#176;C is investigated. An advantage of MAHC over conventional reactors is an even temperature conductance in the reaction medium, as microwaves penetrate the whole reactor volume. This allows a better temperature control and a faster cooldown. Therefore, a succession of depolymerization, transformation and repolymerization reactions can be analyzed effectively. In this study, the analysis of the mass loss, ash content and composition, heating values and molar O/C and H/C ratios of the treated and untreated SCR willow wood showed that the mineral content of the MAHC coal was reduced and the heating value increased. The process water showed a decreasing pH and contained furfural and 5-methylfurfural. A process temperature of 170 &#176;C showed the best combination of energy input and ash component reduction. The MAHC allows a better understanding of the hydrothermal carbonization process, while a large-scale industrial application is unlikely because of the high investment costs.

A protocol for the emission precursor depletion from low quality biomass by low temperature microwave assisted hydrothermal carbonization treatment is presented. This protocol includes the microwave parameters and the analysis of the biocoal product and process water.

Biomass is a sustainable fuel, as its CO2 emissions are reintegrated in biomass growth. However, the inorganic precursors in the biomass cause a negative ...

Microwave-Assisted Preparation of 1-Aryl-1H-pyrazole-5-amines

A synthetic process for the preparation of a variety of 1-aryl-1H-pyrazole-5-amines was developed. The microwave-mediated nature of this method makes it efficient in both time and resources and utilizes water as the solvent. 3-Aminocrotononitrile or an appropriate &#945;-cyanoketone is combined with an aryl hydrazine and dissolved in 1 M HCl. The mixture is then heated in a microwave reactor at 150 &#176;C, typically for 10-15 min. The product can be readily obtained by basifying the solution with 10% NaOH and isolating the desired compound with a simple vacuum filtration. The use of water as a solvent in this reaction lends to its ease and utility in production, and this method is easily reproducible with a variety of functional groups. Typical isolated yields range from 70-90%, and reactions can be performed on the milligram to gram scale with little to no change in observed yields. Some of the applications of these molecules and their derivatives include pesticides, anti-malarials, and chemotherapeutics, among many others.

Microwave-Assisted Preparation of 1-Aryl-1H-pyrazole-5-amines

1-Aryl-1H-pyrazole-5-amines are prepared from aryl hydrazines combined with either 3-aminocrotononitrile or an &#945;-cyanoketone in a 1 M HCl solution using a microwave reactor. Most reactions are done in 10-15 minutes and pure product can be obtained via vacuum filtration with typical isolated yields of 70-90%.

A synthetic process for the preparation of a variety of 1-aryl-1H-pyrazole-5-amines was developed. The microwave-mediated nature of this method makes it ...

A Microwave-Assisted Direct Heteroarylation of Ketones Using Transition Metal Catalysis

Heteroarylation introduces heteroaryl fragments to organic molecules. Despite the numerous available reactions reported for arylation via transition metal catalysis, the literature on direct heteroarylation is scarce. The presence of heteroatoms such as nitrogen, sulfur and oxygen often make heteroarylation a challenging research field due to catalyst poisoning, product decomposition and the rest. This protocol details a highly efficient direct &#945;-C(sp3) heteroarylation of ketones under microwave irradiation. Key factors for successful heteroarylation include the use of XPhos Palladacycle Gen. 4 Catalyst, excess base to suppress side reactions and the high temperature and pressure achieved in a sealed reaction vial under microwave irradiation. The heteroarylation compounds prepared by this method were fully characterized by proton nuclear magnetic resonance spectroscopy (1H NMR), carbon nuclear magnetic resonance spectroscopy (13C NMR) and high-resolution mass spectrometry (HRMS). This methodology has several advantages over literature precedents including broad substrate scope, rapid reaction time, greener procedure and operational simplicity by eliminating the preparation of intermediates such as silyl enol ether. Possible applications for this protocol include, but are not limited to, diversity-oriented synthesis for the discovery of biologically active small molecules, domino synthesis for the preparation of natural products and ligand development for new transition metal catalytic systems.

Heteroaryl compounds are important molecules utilized in organic synthesis, medicinal and biological chemistry. A microwave-assisted heteroarylation using palladium catalysis provides a rapid and efficient method to attach heteroaryl moieties directly to ketone substrates.

Heteroarylation introduces heteroaryl fragments to organic molecules. Despite the numerous available reactions reported for arylation via transition metal ...