Development of the synthesis methods for catalytic aerogels was funded through National Science Foundation (NSF) grant No. DMR-1206631. The design and construction of UCAT was funded through NSF grant No. CBET-1228851. Additional funding was provided by the Union College Faculty Research fund. The authors would also like to acknowledge the contributions of Zachary Tobin, Aude Bechu, Ryan Bouck, Adam Forti, and Vinicius Silva.

Safety Considerations: Wear safety glasses or goggles and laboratory gloves at all times when performing preparatory work with chemical solutions and when handling wet gels or catalytic aerogel materials. Handle propylene oxide, tetramethyl orthosilicate (TMOS), ethanol, methanol, ammonia, nanoparticles and solutions containing any of these within a fume hood. Read Safety Data Sheets (SDS) for all chemicals, including nanoparticles, prior to working with them. Wear a particulate mask when crushing aerogel samples and dur...

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Rev. 37, 515-556 (1995).</li><li>Vallribera, A., Molins, E., Astruc, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aerogel+Supported+Nanoparticles+in+Catalysis.">Aerogel Supported Nanoparticles in Catalysis.</a> Nanoparticles and Catalysis. , (2007).</li><li>Amonette, J. E., Matyas, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functionalized+silica+aerogels+for+gas-phase+purification,+sensing,+and+catalysis:+A+review.">Functionalized silica aerogels for gas-phase purification, sensing, and catalysis: A review.</a> Mircopor. Mesopor. Mater. 250, 100-119 (2017).</li><li>Juhl, S. J., Dunn, N. J. H., Carroll, M. K., Anderson, A. M., Bruno, B. A., Madero, J. E., Bono, M. 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B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Method+and+Device+for+Fabricating+Aerogels+and+Aerogel+Monoliths+Obtained+Thereby.">Method and Device for Fabricating Aerogels and Aerogel Monoliths Obtained Thereby.</a> US Patent No. , (2008).</li><li>Gauthier, B. M., Anderson, A. M., Bakrania, S. D., Mahony, M. K., Bucinell, R. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Method+and+Device+for+Fabricating+Aerogels+and+Aerogel+Monoliths+Obtained+Thereby.">Method and Device for Fabricating Aerogels and Aerogel Monoliths Obtained Thereby.</a> US Patent. , (2011).</li><li>Roth, T. B., Anderson, A. M., Carroll, M. 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The utility of the RSCE method for fabrication of catalytic aerogels and the UCAT system for demonstrating catalytic ability has been demonstrated herein. Major advantages of these protocols over other methods are the speed of RSCE aerogel fabrication and the relatively inexpensive approach to catalytic testing by UCAT.
Gels to be extracted can be prepared via a variety of methods, including impregnation of metal salts into an alumina or silica wet gel matrix, inclusion of metal salts as co-pr...

Silica- and alumina-based aerogels have remarkable properties, including low density, high porosity, high surface area, good thermal stability and low thermal conductivity1. These properties render the aerogel materials attractive for a variety of applications1,2. One application that exploits the thermal stability and high surface area of aerogels is heterogeneous catalysis; several articles review the literature in this area2,3,4,5. There are many approaches to the fabrication of aerogel-based catalysts, including incorporation or entrapment of catalytic species within the framework of a silica or alumina aerogel5,6,7,8,9,10,11. The present work focuses on protocols for preparation via rapid supercritical extraction (RSCE) and catalytic testing of aerogel materials for automotive pollution mitigation, and uses copper-containing aerogels as examples.
Three-way catalysts (TWCs) are commonly employed in pollution mitigation equipment for gasoline engines12. Modern TWCs contain platinum, palladium and/or rhodium, platinum-group metals (PGMs) that are rare and, therefore, expensive and environmentally costly to obtain. Catalyst materials based on more readily available metals would have significant economic and environmental advantages.
Aerogels can be prepared from wet gels using a variety of methods1. The goal is to avoid pore collapse as solvent is removed from the gel. The process employed in this protocol is a rapid supercritical extraction (RSCE) method in which the extraction occurs from a gel confined within a metal mold in a programmable hydraulic hot press13,14,15,16. The use of this RSCE process for the fabrication of silica aerogel monoliths has been previously demonstrated in a protocol17, in which the relatively short preparation time associated with this approach was emphasized. Supercritical CO2 extraction is a more common approach, but takes more time and requires greater use of solvents (including CO2) than RSCE. Other groups have recently published protocols for preparation of a variety of types of aerogels utilizing supercritical CO2 extraction18,19,20.
Here, protocols for fabricating and catalytically testing a variety of types of copper-containing catalytic aerogels are presented. Based on the NO reduction and CO oxidation activity ranking of carbon-supported base metal catalysts under conditions of interest to automotive pollution mitigation provided by Kapteijn et al.21, copper was selected as the catalytic metal for this work. Fabrication approaches include (a) impregnation (IMP) of copper salts into alumina or silica wet gels11, (b) using copper(II) and aluminum salts as co-precursors (Co-P) when fabricating copper-alumina aerogels6,22, and (c) entrapping copper-containing nanoparticles into a silica aerogel matrix during fabrication10. In each case, an RSCE method is used for removal of solvent from the pores of the wet gel matrix13,14,15.
A protocol for assessment of the suitability of these materials as TWCs for automotive pollution mitigation, using the Union Catalytic Testbed (UCAT)23, is also presented. The purpose of the UCAT system, key portions of which are shown schematically in Figure 1, is to simulate the chemical, thermal, and flow conditions experienced in a typical gasoline engine catalytic converter. UCAT functions by passing a simulated exhaust mixture over an aerogel sample at a controlled temperature and flow rate. The aerogel sample is loaded into a 2.25-cm-diameter tubular packed bed flow cell (&#34;test section&#34;), which contains the sample between two screens. The loaded flow cell is placed into an oven to control the exhaust gas and catalyst temperature, and samples of treated exhaust (i.e. exhaust flowed through the packed bed) and untreated gas (i.e. bypassing the packed bed) are examined at a range of temperatures up to 700 &#730;C. The concentrations of the three key pollutants -- CO, NO, and unburned hydrocarbons (HCs) -- are measured using a five-gas analyzer after being treated by the aerogel catalyst and, separately, in an untreated (&#34;bypass&#34;) flow; from these data the &#34;percent conversion&#34; for each pollutant is calculated. For the testing described herein, a commercially available exhaust blend, California Bureau of Automotive Repair (BAR) 97 LOW emissions blend was employed. Full details of the UCAT&#39;s design and functioning are presented in Bruno et al.23
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57075/57075fig1.jpg" /> 
Figure 1. UCAT Test Section and Sampling Systems. Reprinted with permission from 2016-01-0920 (Bruno et al.23), Copyright 2016 SAE International. Further distribution of this material is not permitted without prior permission from SAE. <a href="//cloudflare.jove.com/files/ftp_upload/57075/57075fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<table border="0" cellpadding="0" cellspacing="0" width="670">
	<tbody>
		<tr height="76">
			<td height="76" style="height:76px;width:216px;">Variable micropipettor, 100-1000 &#181;L</td>
			<td style="width:168px;">Manufactured by Eppendorf, purchased from Fisher Scientific www.fishersci.com</td>
			<td style="width:119px;">S304665</td>
			<td style="width:167px;">Any 100-1000 &#181;L pipettor is suitable.</td>
		</tr>
		<tr height="76">
			<td height="76" style="height:76px;width:216px;">Variable Pipettor, 2.5-10 mL</td>
			<td style="width:168px;">Manufactured by Eppendorf, purchased from Fisher Scientific www.fishersci.com</td>
			<td style="width:119px;">21-379-25</td>
			<td style="width:167px;">Any variable pipettor is suitable.</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Pasteur pipettes</td>
			<td style="width:168px;">FisherScientific</td>
			<td style="width:119px;">13-678-6A</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="57">
			<td height="57" style="height:57px;width:216px;">Syringe</td>
			<td style="width:168px;">Purchased from Fisher Scientific</td>
			<td style="width:119px;">Z181390 syringe with Z261297 needle</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="38">
			<td height="38" style="height:38px;width:216px;">Digital balance</td>
			<td style="width:168px;">OHaus Explorer Pro</td>
			<td style="width:119px;"></td>
			<td style="width:167px;">Any digital balance is suitable.</td>
		</tr>
		<tr height="38">
			<td height="38" style="height:38px;width:216px;">Beakers</td>
			<td style="width:168px;">Purchased from Fisher Scientific</td>
			<td style="width:119px;"></td>
			<td style="width:167px;">Any glass beaker is suitable.</td>
		</tr>
		<tr height="38">
			<td height="38" style="height:38px;width:216px;">Graduated Cylinder</td>
			<td style="width:168px;">Purchased from Fisher Scientific</td>
			<td style="width:119px;"></td>
			<td style="width:167px;">Any glass graduated cylinder is suitable.</td>
		</tr>
		<tr height="38">
			<td height="38" style="height:38px;width:216px;">Magnetic Plate/Stirrer</td>
			<td style="width:168px;">FisherScientific Isotemp</td>
			<td style="width:119px;">SP88854200P</td>
			<td style="width:167px;">Any magnetic plate/stirrer is suitable.</td>
		</tr>
		<tr height="38">
			<td height="38" style="height:38px;width:216px;">Ultrasonic Cleaner</td>
			<td style="width:168px;">FisherScientific FS6</td>
			<td style="width:119px;">153356</td>
			<td style="width:167px;">Any sonicator is suitable.</td>
		</tr>
		<tr height="57">
			<td height="57" style="height:57px;width:216px;">Mold</td>
			<td style="width:168px;">Fabricated in House</td>
			<td style="width:119px;"></td>
			<td style="width:167px;">Fabricate from cold-rolled steel or stainless steel.</td>
		</tr>
		<tr height="133">
			<td height="133" style="height:133px;width:216px;">Hydraulic Hot Press</td>
			<td style="width:168px;">Tetrahedron www.tetrahedronassociates.com</td>
			<td style="width:119px;">MTP-14</td>
			<td style="width:167px;">Any hot press with temperature and force control will work. Needs maximum temperature of ~550 F and maximum force of 24 tons.</td>
		</tr>
		<tr height="153">
			<td height="153" style="height:153px;width:216px;">UCAT (Union Catalytic Testbed)</td>
			<td style="width:168px;">Fabricated in House</td>
			<td style="width:119px;"></td>
			<td style="width:167px;">Described in detail in reference #21:&#160; Bruno, B.A., Anderson, A.M., Carroll, M.K., Brockmann, P., Swanton, T., Ramphal, I.A., Palace, T. Benchtop Scale Testing of Aerogel Catalysts. SAE Technical Paper 2016-01-920 (2016).</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Bar 97 Gas</td>
			<td>Praxair</td>
			<td>MS_BAR97ZA-D7</td>
			<td></td>
		</tr>
	</tbody>
</table>

fabrication and testing of catalytic aerogels prepared via rapid supercritical extraction

Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three preparation methods are described: (a) the incorporation of metal salts into silica or alumina wet gels using an impregnation method; (b) the incorporation of metal salts into alumina wet gels using a co-precursor method; and (c) the addition of metal nanoparticles directly into a silica aerogel precursor mixture. The methods utilize a hydraulic hot press, which allows for rapid (&#60;6 h) supercritical extraction and results in aerogels of low density (0.10 g/mL) and high surface area (200-800 m2/g). While the work presented here focuses on the use of copper salts and copper nanoparticles, the approach can be implemented using other metal salts and nanoparticles. A protocol for testing the three-way catalytic ability of these aerogels for automotive pollution mitigation is also presented. This technique uses custom-built equipment, the Union Catalytic Testbed (UCAT), in which a simulated exhaust mixture is passed over an aerogel sample at a controlled temperature and flow rate. The system is capable of measuring the ability of the catalytic aerogels, under both oxidizing and reducing conditions, to convert CO, NO and unburned hydrocarbons (HCs) to less harmful species (CO2, H2O and N2). Example catalytic results are presented for the aerogels described.

Photographic images of the resulting aerogels are presented in Figure 2. Because the wet gels were broken into pieces prior to solvent exchange, the Al-Cu IMP and Si-Cu IMP aerogels are in small, irregularly shaped monolithic pieces. It is clear from the coloration of these samples that the aerogels contain copper species and that variations in copper speciation and/or ligand structure occur within the materials. Al-Cu IMP aerogels (Figur...

Watch this Scientific Journal Video about Fabrication and Testing of Catalytic Aerogels Prepared Via Rapid Supercritical Extraction at JoVE.com

Fabrication and Testing of Catalytic Aerogels Prepared Via Rapid Supercritical Extraction

Here we present protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms. Methods for preparing materials using copper salts and copper-containing nanoparticles are featured. Catalytic testing protocols demonstrate the effectiveness of these aerogels for three-way catalysis applications.

Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three ...

This method can lead to the development of new materials for automotive catalysis applications without reliance on precious metals. The main advantage of this technique is that a variety of high-performing catalytic aerogels can be prepared and tested relatively quickly. We first had the idea for this application of the RSCE method and development of a catalytic test bed when working with a former student to develop an undergraduate thesis project.Visual demonstration of this method is valuable, as the catalytic test bed is not a commercially-available instrument. Using a calibrated digital balance, weigh out 5.92 grams of aluminum chloride hexahydrate and add to a 250 milliliter beaker. Add 40 milliliters of reagent-grade ethanol and a stir bar to the beaker.Cover the beaker with paraffin film and place on a magnetic stir plate for stirring at moderate speed, until the aluminum salt has dissolved. Then, remove the beaker from the magnetic plate and uncover. Using a 10 milliliter syringe, add eight milliliters of propylene oxide to the beaker containing the aluminum chloride solution.Replace the paraffin film on the beaker and place on the magnetic stir plate for stirring at moderate speed until the solution has gelled. Following this, remove the beaker from the magnetic stir plate and allow the gel to age at room temperature for 24 hours. Using the calibrated digital balance, weigh out 1.4 grams of copper nitrate trihydrate.Add this salt to 40 milliliters of absolute ethanol in a beaker. Then, place the beaker in a sonicator and sonicate until the copper salt dissolves. Now, pour any excess solvent off the alumina sol gel.Remove the stir bar and break the gel into several pieces using a spatula. Transfer the copper solution to the 250 milliliter beaker containing the gel pieces. Then, cover the beaker with paraffin film and allow the gel to age at room temperature for 24 hours.On the following day, remove the excess solvent and add 40 milliliters of fresh absolute ethanol. Replace the paraffin film on the beaker, and allow the gel to age for another 24 hours at room temperature. Obtain an appropriately-sized stainless steel mold.To prepare the gasket material, cut ceiling gaskets sufficient in size to fully cover the mold from a 1.6 millimeter thick graphite gasket sheet and a 0.012 millimeter thick stainless steel foil. Following this, program the hot press for ethanol extraction. Following preparation and ethanol exchange of the wet sol gels, decant the excess solvent.Now, distribute the wet sol gels into the wells of the mold and center the mold on the hot press heating plate. Top off each well with absolute ethanol. Place the stainless steel foil, followed by the graphite sheet on to the top of the mold to seal it.Then, begin the hot press extraction program. Once the process is complete, remove the mold from the hot press. Then, remove the gasket material from the mold and transfer the aerogels into sample containers.Place a clean 250 milliliter beaker on the calibrated digital balance and pipette approximately 13 milliliters of TMOS into the beaker. Add additional TMOS as needed for a total of 13.04 grams of TMOS. Next, pipette 32.63 grams of methanol and 3.90 grams of deionized water into the beaker.Shake the previously prepared 20 weight percent copper two oxide nanodispersion to resuspend any nanoparticles that have settled to the bottom. Pipette 1.5 grams of the nanodispersion into the beaker of precursor solution. Then, pipette 200 microliters of 1.5 molar ammonia solution into the beaker.Cover the beaker with paraffin film and sonicate the mixture for five-10 minutes, until it is a monophasic solution. After heating the aerogel in a furnace, pour 20 milliliters of the cooled material in a clean, day, UCAT test section and insert an end screen to retain the sample in place during testing. Following this, load the test section into the UCAT assembly using copper washers and clamps to seal.Then, securely close the UCAT oven. After setting up the five gas analyzers, set the desired oven temperature and start the oven. Ensure that the bypass valve is set to deliver air through the test cell.Next, adjust the mass flow rate controllers to deliver the correct quantities of air used during warm-up and simulated exhaust used during testing to maintain the desired space velocity. Turn on the warm-up air flow to purge the test cell and wait for the flow through the test cell to stabilize at the desired test temperature, typically, 30 minutes. Now, re-zero the five gas analyzer and set the bypass valve to send the flow to bypass the test section.Turn off the air. Turn on the simulated exhaust flow. Allow the five gas analyzer readings to stabilize for approximately 90 seconds and record the bypass pollutant concentrations.Next, set the bypass valve to direct the flow through the test section. Allow the five gas analyzer readings to stabilize for approximately 360 seconds and record the treated no-oxygen exhaust pollutant concentrations. Turn on the oxygen addition to the blend.Allow the five gas analyzer readings to stabilize for approximately 90 seconds and record the treated-with-oxygen exhaust pollutant concentrations. Following this, set the bypass valve to send the flow to bypass the test section. Allow the five gas analyzer readings to stabilize for approximately 90 seconds and record the bypass pollutant concentrations again.Finally, turn off the simulated exhaust flow. Representative physical characteristics of the as-prepared copper-containing aerogels are listed here. A 400 nanometer-diameter nanoparticle containing copper is observed in the EDX image of the silica copper nanoparticle aerogel, prepared using the copper two nanodispersion.This indicates that some agglomeration of the 25-55 nanometer nanoparticles in the original nanodispersion has occurred. Smaller nanoparticles are observed in the alumina copper impregnated aerogel. The XRD pattern of the as-prepared silica copper impregnated and nanoparticle aerogels contain peaks corresponding to metallic copper.This indicates the alcohol thermal reduction of the copper species occurred during RSCE processing of the gels. The as-prepared alumina copper-impregnated aerogel pattern shows XRD peaks consistent with the pseudo-boehmite form of alumina and a copper two-containing species. Copper-containing alumina aerogels are capable of catalyzing reactions that can eliminate each of the three major pollutants of concern in gasoline engine exhaust under the conditions tested.The catalytic ability in copper-containing silica aerogels is shown here and provides evidence that the catalytic capabilities of metal-doped aerogels are robust and tailorable. The catalytic activity appears to depend on how copper is introduced to the sol-gel mixture and the underlying aerogel itself. Once mastered, catalytic aerogel preparation takes about one to two hours, followed by as little as three hours to process the mixture to yield aerogels.Following this procedure, other types of metal-containing catalytic aerogels can be fabricated for automotive pollution mitigation or other applications. After watching this video, you should have a good understanding of how the test bed can be used to gain information about the aerogel's catalytic performance. Working with TMOS, propylene oxide, the hot press, and simulated automotive exhaust can be extremely hazardous.Precautions such as wearing personal protective gear and working under proper ventilation should always be taken when performing these procedures.

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Research

JoVE Journal

Chemistry

7.2K Views.  Union College. This method can lead to the development of new materials for automotive catalysis applications without reliance on precious metals. The main advantage of this technique is that a variety of high-performing catalytic aerogels can be prepared and tested relatively quickly. We first had the idea for this application of the RSCE method and development of a catalytic test bed when working with a former student to develop an undergraduate thesis project.Visual demonstration of this method is...