Name: temperature-programmed deoxygenation of acetic acid on molybdenum carbide catalysts
Uploaded: 2017-02-07T15:00:00
Description: Watch this Scientific Journal Video about Temperature-programmed Deoxygenation of Acetic Acid on Molybdenum Carbide Catalysts at JoVE.com

This work was supported by the Department of Energy Bioenergy Technologies Office under Contract no. DE-AC36-08-GO28308. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.

CAUTION: Consult safety data sheets (SDS) for all chemicals used prior to operation. Flammable gases may present explosion hazards if combined with air or oxygen and an ignition source. Hydrogen is an extremely flammable gas. Acids are corrosive, and in the case of skin or eye contact, are irritants and may produce burns. Acetic acid is a flammable liquid and vapor and thus may ignite and/or explode in the presence of open flames, sparks and oxidizing agents, in addition to potentially causing severe skin burns and eye d...

<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=Vanadia/Titania+Catalysts+for+Selective+Catalytic+Reduction+(SCR)+of+Nitric-Oxide+by+Ammonia.">Vanadia/Titania Catalysts for Selective Catalytic Reduction (SCR) of Nitric-Oxide by Ammonia.</a> J Catal. 151 (1), 226-240 (1995).</li><li>Clarke, D. B., Bell, A. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+Infrared+Study+of+Methanol+Synthesis+from+CO2+on+Clean+and+Potassium-Promoted+Cu/SiO2.">An Infrared Study of Methanol Synthesis from CO2 on Clean and Potassium-Promoted Cu/SiO2.</a> J Catal. 154 (2), 314-328 (1995).</li><li>Schaidle, J. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+and+Computational+Investigation+of+Acetic+Acid+Deoxygenation+over+Oxophilic+Molybdenum+Carbide:+Surface+Chemistry+and+Active+Site+Identity.">Experimental and Computational Investigation of Acetic Acid Deoxygenation over Oxophilic Molybdenum Carbide: Surface Chemistry and Active Site Identity.</a> ACS Catal. 6 (2), 1181-1197 (2016).</li><li>Ruddy, D. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recent+advances+in+heterogeneous+catalysts+for+bio-oil+upgrading+via+"ex+situ+catalytic+fast+pyrolysis":+catalyst+development+through+the+study+of+model+compounds.">Recent advances in heterogeneous catalysts for bio-oil upgrading via "ex situ catalytic fast pyrolysis": catalyst development through the study of model compounds.</a> Green Chem. 16 (2), 454-490 (2014).</li><li>Dutta, A., Schaidle, J. A., Humbird, D., Baddour, F. G., Sahir, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Conceptual+Process+Design+and+Techno-Economic+Assessment+of+Ex+Situ+Catalytic+Fast+Pyrolysis+of+Biomass:+A+Fixed+Bed+Reactor+Implementation+Scenario+for+Future+Feasibility.">Conceptual Process Design and Techno-Economic Assessment of Ex Situ Catalytic Fast Pyrolysis of Biomass: A Fixed Bed Reactor Implementation Scenario for Future Feasibility.</a> Top. Catal. 59 (1), 2-18 (2016).</li><li>Venkatakrishnan, V. K., Delgass, W. N., Ribeiro, F. 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The TPRxn method is a powerful tool for screening of catalytic materials, providing information about the activity and selectivity of a catalyst as a function of reaction temperature. Other temperature-programmed methods such as TPD, TPO and TPR can provide information on the adsorption strength of reactants, number of adsorption sites, and appropriate catalyst pre-treatment procedures, but do not provide direct catalytic performance data. It is important to note that the TPRxn method detailed in this work does not measu...

Temperature programmed reaction (TPRxn) is one of many temperature programmed methods, including desorption (TPD), oxidation (TPO), and reduction (TPR), and proceeds via exposure of a catalyst to a reactant concurrent with or followed by a steady increase in temperature.1,2,3 TPRxn is a transient technique that provides information about catalyst activity and selectivity as a function of reaction temperature.4,5,6 It is also a popular technique: a search of the keywords &#39;temperature programmed reaction&#39; in the literature yields over 1,000 sources citing its use.
TPRxn experiments are typically performed in a microreactor system, equipped with a mass spectrometer (MS) for real-time analysis of the reactor effluent and correlation of performance with temperature. Reactant gases can be introduced using mass flow controllers and liquids can be introduced via a syringe pump or as vapors by bubbling inert gas through a liquid. The catalyst is often pre-treated in situ to form the desired catalytic phase for the reaction. Some systems are equipped with additional analytical equipment, beyond the typical mass spectrometer, to provide quantitative or qualitative information about the catalyst selectivity, surface species present on the catalyst, or reaction mechanism. For example, temperature programmed in situ Fourier Transform Infrared Spectroscopy (FTIR) provides information about the evolution of surface species with varying reaction temperature.7,8 The TPRxn system demonstrated in this work is equipped with a gas chromatogram (GC) in addition to the more typical MS. This GC, equipped with four parallel columns, allows for more accurate quantification of the reaction products, but is limited in analysis frequency by the time it takes the products to elute through the columns. Thus, the combination of MS and GC can be particularly useful for coupling real-time identification with accurate quantification of reactants and products.
Here, we apply the TPRxn methodology to study the deoxygenation of acetic acid on molybdenum carbide catalysts. This is an interesting and important reaction in catalyst research, as acetic acid is a useful analog for the many carboxylic acids present in biomass pyrolysis vapors.9 The high oxygen content in biomass pyrolysis vapors necessitates oxygen removal to produce hydrocarbon fuels,10,11,12 and molybdenum carbide catalysts have shown promising deoxygenation performance for many biomass pyrolysis vapor model compounds, including furfural, 1-propanol, phenolics and acetic acid.9,13,14,15,16 However, the activity and selectivity of molybdenum carbide catalysts in deoxygenation reactions is dependent on the catalyst structure and composition, the reacting species and the reaction conditions.
The data collected from TPRxn of acetic acid shows that molybdenum carbide catalysts are active for deoxygenation reactions above ca. 300 &#176;C, and when combined with catalyst characterization information allows for quantification of the catalyst activity as a function of temperature via the calculation of acetic acid turnover rates. The TPRxn results show that deoxygenation (i.e., C-O bond-breaking) products are favored at temperatures below ca. 400 &#176;C and decarbonylation (i.e., C-C bond-breaking) products are favored at temperatures above ca. 400 &#176;C. Additionally, TPRxn studies illustrate the changes in the activity and selectivity of molybdenum carbide catalysts produced using various synthetic procedures (i.e., the production of different molybdenum carbide catalyst structures and compositions). Still, the value of this information and, more generally, the successful application of TPRxn experimental data toward catalyst design and process optimization is a function of the quality of the data obtained. Careful consideration and knowledge of the potential difficulties and limitations highlighted throughout the TPRxn procedure is paramount.

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	<tbody>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">glacial acetic acid</td>
			<td style="width:179px;">Cole-Parmer</td>
			<td style="width:148px;">EW-88401-62</td>
			<td style="width:401px;">alternate supplier acceptable if ACS purity grade. See caution statement in protocol for safety information</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">UHP H&#8322;</td>
			<td style="width:179px;">Airgas</td>
			<td style="width:148px;">HY R300</td>
			<td>alternate supplier acceptable if &#62;99.99% purity</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">UHP He</td>
			<td style="width:179px;">Airgas</td>
			<td style="width:148px;">HE R300SS</td>
			<td>alternate supplier acceptable if &#62;99.99% purity</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">UHP Ar</td>
			<td style="width:179px;">Arigas</td>
			<td style="width:148px;">AR R200</td>
			<td>alternate supplier acceptable if &#62;99.99% purity</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">acetone</td>
			<td style="width:179px;">VWR International</td>
			<td style="width:148px;">BDH1101-4LP</td>
			<td>alternate supplier acceptable if &#62;99.5% purity</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">quartz chips</td>
			<td style="width:179px;">Powder Technology Inc.</td>
			<td style="width:148px;">Crushed Quartz</td>
			<td style="width:401px;">sieved 180-300 &#181;m, calcined in air at 500 &#176;C overnight</td>
		</tr>
		<tr height="56">
			<td height="56" style="height:56px;width:215px;">mass spectrometer - turbo vacuum pump</td>
			<td style="width:179px;">Pfeiffer Vacuum</td>
			<td style="width:148px;">TSU 071</td>
			<td style="width:401px;">mass spectrometer is controlled with LabVIEW 2010 software package (National Instruments)</td>
		</tr>
		<tr height="56">
			<td height="56" style="height:56px;width:215px;">mass spectrometer - turbo vacuum pump</td>
			<td style="width:179px;">Stanford Research Systems</td>
			<td style="width:148px;">RGA100</td>
			<td style="width:401px;"></td>
		</tr>
		<tr height="126">
			<td height="126" style="height:126px;width:215px;">micro gas chromatograph</td>
			<td style="width:179px;">Agilent</td>
			<td style="width:148px;">CP740388</td>
			<td style="width:401px;">490 Micro GC; 4-channel system 
			Channel 1: 494001360 Molseive 10m, heated backflush 
			Channel 2: 494001460 PPU 10m, heated backflush 
			Channel 3: 490040 AL2O3/KCL 10+0.2m, heated backflush SPECIAL 
			Channel 4: 492005750 5CB 15m, heated</td>
		</tr>
		<tr height="56">
			<td height="56" style="height:56px;width:215px;">GC software</td>
			<td style="width:179px;">Aglient</td>
			<td style="width:148px;">OpenLAB CDS EZChrom Edition</td>
			<td style="width:401px;"></td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">clean gas filters</td>
			<td style="width:179px;">Agilent</td>
			<td style="width:148px;">CP17974</td>
			<td>for use on GC carrier gases (He, Ar)</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">quartz &#34;U-tube&#34; reactor</td>
			<td style="width:179px;">n/a</td>
			<td style="width:148px;"></td>
			<td>hand blown glass, custom built to order</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">bubbler</td>
			<td style="width:179px;">n/a</td>
			<td style="width:148px;"></td>
			<td>custom built to order</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">ceramic furnace</td>
			<td style="width:179px;">Watlow</td>
			<td style="width:148px;">discontinued</td>
			<td>Similar furnace part #: VC401J12A-B000R</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">heat tape controller</td>
			<td style="width:179px;">n/a</td>
			<td style="width:148px;"></td>
			<td>custom built with Watlow EZ-zone parts</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">heat tape</td>
			<td style="width:179px;">Omega</td>
			<td style="width:148px;">FGH051-060</td>
			<td style="width:401px;">alternate supplier for extreme temperature heat tape acceptable</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">heat tape insulation</td>
			<td style="width:179px;">JEGS</td>
			<td style="width:148px;">710-80809</td>
			<td>alternate supplier acceptable</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">thermocouple</td>
			<td style="width:179px;">Omega</td>
			<td style="width:148px;">e.g., KMQSS-062U-18</td>
			<td>K-type thermocouples; alternate sizes may be required</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">thermocouple o-ring</td>
			<td style="width:179px;">Swagelok</td>
			<td style="width:148px;">VT-7-OR-001-1/2</td>
			<td>perfluoroelastomer(fluorocarbon FKM) o-ring</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">2 &#181;m solids filter, VCR gasket</td>
			<td style="width:179px;">Swagelok</td>
			<td style="width:148px;">SS-4-VCR-2-2M</td>
			<td></td>
		</tr>
		<tr height="57">
			<td height="57" style="height:58px;width:215px;">1 &#181;m orifice, VCR gasket</td>
			<td style="width:179px;">Lenox Laser</td>
			<td style="width:148px;">SS-4-VCR-2</td>
			<td>for mass spectrometer orifice</td>
		</tr>
		<tr height="93">
			<td height="93" style="height:94px;width:215px;">316/316L stainless steel tubing and fittings</td>
			<td style="width:179px;">Swagelok</td>
			<td style="width:148px;">Varies</td>
			<td style="width:401px;">See Swagelok &#39;VCR Metal Gasket Face Seal Fittings&#39; and &#39;Stainless Steel Seamless Tubing and Tube Support Systems&#39; catalogs for more information</td>
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			<td style="width:401px;">See Swagelok &#39;Integral-Bonnet Needle Valves&#39;, &#39;Bellows-Sealed Valves&#39; and &#39;One-Piece Instrumentation Ball Valves&#39; catalogs for more information</td>
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temperature-programmed deoxygenation of acetic acid on molybdenum carbide catalysts

Temperature programmed reaction (TPRxn) is a simple yet powerful tool for screening solid catalyst performance at a variety of conditions. A TPRxn system includes a reactor, furnace, gas and vapor sources, flow control, instrumentation to quantify reaction products (e.g., gas chromatograph), and instrumentation to monitor the reaction in real time (e.g., mass spectrometer). Here, we apply the TPRxn methodology to study molybdenum carbide catalysts for the deoxygenation of acetic acid, an important reaction among many in the upgrading/stabilization of biomass pyrolysis vapors. TPRxn is used to evaluate catalyst activity and selectivity and to test hypothetical reaction pathways (e.g., decarbonylation, ketonization, and hydrogenation). The results of the TPRxn study of acetic acid deoxygenation show that molybdenum carbide is an active catalyst for this reaction at temperatures above ca. 300 &#176;C and that the reaction favors deoxygenation (i.e., C-O bond-breaking) products at temperatures below ca. 400 &#176;C and decarbonylation (i.e., C-C bond-breaking) products at temperatures above ca. 400 &#176;C.

The online MS provides the capability to analyze the gas composition at the reactor outlet in real-time. The online MS is not coupled with any device to separate products prior to analysis, and thus species identification is challenging when differentiating between compounds with overlapping mass fragmentation patterns. As shown in Table 2, many of the common products from acetic acid TPRxn experiments are characterized by multiple common m/z signals. Deconvolution of the...

Watch this Scientific Journal Video about Temperature-programmed Deoxygenation of Acetic Acid on Molybdenum Carbide Catalysts at JoVE.com

Temperature-programmed Deoxygenation of Acetic Acid on Molybdenum Carbide Catalysts

Presented here is a protocol for the operation of a micro-scale temperature-programmed reactor for evaluating the catalytic performance of molybdenum carbide during acetic acid deoxygenation.

Temperature programmed reaction (TPRxn) is a simple yet powerful tool for screening solid catalyst performance at a variety of conditions. A TPRxn system ...

The overall goal of this temperature-programmed reaction method is to determine the deoxygenation performance of molybdenum carbide catalyst from the pyrolysis oil model compound acetic acid. This method can help answer key questions in the field of vapor phase upgrading using heterogeneous catalysts, such as those regarding catalytic activity and selectivity from pyrolysis oil model compounds. The main advantages of this technique is the ability to test catalytic performance over a range of temperatures in a single experiment.While this method could provide insight into catalytic performance with acetic acid vapors, it can also be applied to other pyrolysis oil model compounds such as acid aldehyde, ethanol, methanol, and anisole. First, remove a clean, dry quartz U-tube reactor from a drying oven. Once the reactor has cooled to room temperature, load a small amount of quartz wool into it using the minimum amount needed to support the catalyst bed.Using a clean, stiff metal wire packing word, gently push the wool down the quartz tube to the end of the straight section. Next, mix 50 milligrams of molybdenum carbide catalyst with 200 milligrams of sieved calcined quartz chips to prevent channeling and to ensure consistent temperature through the catalyst bed. Using weigh paper and a clean funnel, pour the catalyst and quartz chip mixture into the reactor such that the catalyst bed sits on top of the quartz wool support.Then, gently push a second small piece of quartz wool on top of the catalyst bed, securing the catalyst bed in place. It's important to ensure that the catalyst-quartz chip mixture is homogenous. Inhomogeneous mixtures can lead to channeling, temperature gradients, and an excessive pressure drop across the catalyst bed.Install the reactor by first connecting and tightening the fitting on the upstream side of the catalyst bed, which is the straight section of the reactor tube. Then, connect and tighten the fitting on the downstream side of the catalyst bed. Next, adjust the reactor thermocouple position by pushing the thermocouple through a bored-through fitting so that the tip of the thermocouple sits on the top edge of the catalyst bed.Install insulation around the upper section of the reactor, and then carefully raise the furnace to the highest level allowed by the U-tube reactor such that the top edge of the furnace does not touch the reactor. Begin purging the system by flowing ultra-high purity helium at 40 sccm through the calibrated mass flow controller, or MFC. Following this, open the mass spectrometer, or MS orifice valve, to allow gas to reach the MS ion source.After opening the hydrogen tank cylinder and regulator needle valves, begin flowing ultra-high purity hydrogen, but opening the system line shutoff valve immediately downstream of the hydrogen MFC and setting the MFC to flow at 1.3 sccm. Then, adjust the helium flow to 36 sccm, such that the gas mixture is 3.5%hydrogen. Once the hydrogen and helium gas phase concentrations have stabilized, enter the temperature program into the furnace controller, then begin the temperature program.For the temperature-programmed reaction, begin the flow of acetic acid vapors through the reactor by opening the inlet and outlet saturator valves and subsequently closing the saturator bypass valve. Route the gas flow to the microgas chromatograph, or micro GC, by switching the three-way valve downstream of the reactor to the micro GC position. After allowing the system pressure of acetic acid gas phase concentration to stabilize, program the furnace temperature controller to ramp from room temperature to 600 degrees Celsius at ten degrees Celsius per minute.Now begin collecting micro GC samples as frequently as possible. Begin the temperature program immediately after starting to collect the micro GC samples. When the temperature program has completed, stop the micro GC samples.Using the computer software associated with the MS, turn the MS ion source off, then close the one micrometer MS orifice valve. After the last micro GC sample has completed, load a method that sets the column temperatures to the maximum allowable limit as recommended by the manufacturer. Shut off the hydrogen flow by setting the hydrogen MFC to zero sccm and closing the hydrogen shutoff valve.Shut off the flow of acetic acid vapors to the reactor by opening the saturator bypass valve and closing the inlet and outlet saturator valves. After allowing the reactor to cool to ambient temperature, turn off the helium flow by setting the helium MFC to zero sccm, then close the shutoff valve located immediately downstream of the helium MFC. Once the system has reached ambient pressure, route the gas to the local exhaust ventilation using the three-way valve.Uninstall the reactor by first disconnecting the fitting on the downstream side of the reactor, which is the fitting connected to the flexible stainless steel tubing. Finally, disconnect the fitting on the upstream side of the reactor. As shown here, many of the common products from acetic acid temperature-programmed reaction experiments are characterized by common mass to charge signals in mass spectrometry, and thus signal deconvolution is required.Following deconvolution, the normalized and corrected MS data maybe used semiquantitatively to gather information, such as reactive conversion and relative product concentration as a function of reaction temperature. Representative data from a study comparing the deoxygenation performance of several molybdenum carbide catalysts in an acetic acid temperature-programmed reaction is shown here. A templated nanoparticle molybdenum carbide catalyst demonstrated greater acetic acid turnover rate compared to its untemplated counterpart in similar acetic acid turnover rates compared to the bulk molybdenum carbide catalysts below 400 degrees Celsius.Above 400 degrees Celsius, the templated catalysts demonstrated a greater acetic acid turnover rate than any of the other catalysts studied. The hydrogen turnover rates were lower in the nanoparticle catalysts than on the bulk catalysts at all temperatures. Both nanoparticle materials demonstrated higher selectivity to ketonization products above 400 degrees Celsius than their bulk counterparts, which was attributed to an increase in the fraction of strong acid sites relative to the bulk materials.Furthermore, the ratio of acid sites to hydrogen activation sites was identified as a key property in determining acetic acid deoxygenation performance. This technique can be performed in less than four hours, which makes the temperature-programmed reaction method an effective tool for screening the performance of catalytic materials and their various reaction conditions. After watching this video, you should have a good understanding of how to safely and effectively operate a temperature-programmed reaction using acetic acid vapors.

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