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.

<ol>
	<li>Aegerter, M. A., Leventis, N., Koebel, M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Aerogels Handbook. , (2011).</li><li>Pierre, A. C., Pajonk, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemistry+of+Aerogels+and+Their+Applications.">Chemistry of Aerogels and Their Applications.</a> Chem. Rev. 102 (11), 4243-4266 (2002).</li><li>Schneider, M., Baiker, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aerogels+in+Catalysis.">Aerogels in Catalysis.</a> Catal. 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. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epoxide-Assisted+Alumina+Aerogels+by+Rapid+Supercritical+Extraction.">Epoxide-Assisted Alumina Aerogels by Rapid Supercritical Extraction.</a> J. Non-Cryst. Solids. 426, 141-149 (2015).</li><li>Bono, M. S., Dunn, N. J. H., Brown, L. B., Juhl, S. J., Anderson, A. M., Bruno, B. A., Mahony, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Catalyst,+Catalytic+Converter+and+Method+for+the+Production+Thereof.">Catalyst, Catalytic Converter and Method for the Production Thereof.</a> US Patent. , (2016).</li><li>Smith, L. C., Anderson, A. M., Carroll, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+of+vanadia-containing+aerogels+by+rapid+supercritical+extraction+for+applications+in+catalysis.">Preparation of vanadia-containing aerogels by rapid supercritical extraction for applications in catalysis.</a> J. Sol-Gel Sci. Technol. 77, 160-171 (2016).</li><li>Bouck, R. M., Anderson, A. M., Prasad, C., Hagerman, M. E., Carroll, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cobalt-alumina+Sol+Gels:+Effects+of+Heat+Treatment+on+Structure+and+Catalytic+Ability.">Cobalt-alumina Sol Gels: Effects of Heat Treatment on Structure and Catalytic Ability.</a> J. Non-Cryst. Solids. 453, 94-102 (2016).</li><li>Anderson, A. M., Donlon, E. A., Forti, A. A., Silva, V., Bruno, B. A., Carroll, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+and+Characterization+of+Copper-Nanoparticle-Containing+Silica+Aerogel+Prepared+Via+Rapid+Supercritical+Extraction+for+Applications+in+Three-Way+Catalysis.">Synthesis and Characterization of Copper-Nanoparticle-Containing Silica Aerogel Prepared Via Rapid Supercritical Extraction for Applications in Three-Way Catalysis.</a> MRS Advances. , 1-6 (2017).</li><li>Tobin, Z. M., Posada, L. F., Bechu, A. M., Carroll, M. K., Bouck, R. M., Anderson, A. M., Bruno, B. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+and+Characterization+of+Copper-containing+Alumina+and+Silica+Aerogels+for+Catalytic+Applications.">Preparation and Characterization of Copper-containing Alumina and Silica Aerogels for Catalytic Applications.</a> J. Sol-Gel Sci. Technol. , (2017).</li><li>Heck, R., Farrauto, R., Gulati, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Catalytic Air Pollution Technology. , (2009).</li><li>Gauthier, B. M., Bakrania, S. D., Anderson, A. M., Carroll, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Fast+Supercritical+Extraction+Technique+for+Aerogel+Fabrication.">A Fast Supercritical Extraction Technique for Aerogel Fabrication.</a> J. Non-Cryst. Solids. 350, 238-243 (2004).</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 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. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+a+Rapid+Supercritical+Extraction+Aerogel+Fabrication+Process:+Prediction+of+Thermodynamic+Conditions+During+Processing.">Analysis of a Rapid Supercritical Extraction Aerogel Fabrication Process: Prediction of Thermodynamic Conditions During Processing.</a> J. Non-Cryst. Solids. 354 (31), 3685-3693 (2008).</li><li>Carroll, M. K., Anderson, A. M., Gorka, C. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparing+Silica+Aerogel+Monoliths+via+a+Rapid+Supercritical+Extraction+Method.">Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method.</a> J. Vis. Exp. (84), e51421 (2014).</li><li>Harper-Leatherman, A. S., Pacer, E. R., Kosciuszek, N. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Encapsulating+Cytochrome+c+in+Silica+Aerogel+Nanoarchitectures+without+Metal+Nanoparticles+while+Retaining+Gas-phase+Bioactivity.">Encapsulating Cytochrome c in Silica Aerogel Nanoarchitectures without Metal Nanoparticles while Retaining Gas-phase Bioactivity.</a> J. Vis. Exp. (109), e53802 (2016).</li><li>Subrahmanyam, R., Gurikov, P., Meissner, I., Smirnova, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+of+Biopolymer+Aerogels+Using+Green+Solvents.">Preparation of Biopolymer Aerogels Using Green Solvents.</a> J. Vis. Exp. (113), e54116 (2016).</li><li>Campbell, P. G., Worsley, M. A., Hiszpanski, A. M., Baumann, T. F., Biener, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+and+Functionalization+of+3D+Nano-graphene+Materials:+Graphene+Aerogels+and+Graphene+Macro+Assemblies.">Synthesis and Functionalization of 3D Nano-graphene Materials: Graphene Aerogels and Graphene Macro Assemblies.</a> J. Vis. Exp. (105), e53235 (2015).</li><li>Kapteijn, F., Stegenga, S., Dekker, N. J. J., Bijsterbosch, J. W., Moulijn, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Alternatives+to+noble+metal+catalysts+for+automotive+exhaust+purification.">Alternatives to noble metal catalysts for automotive exhaust purification.</a> Catalysis Today. 16 (2), 273-287 (1993).</li><li>Baumann, T., Gash, A., Chinn, S., Sawvel, A., Maxwell, R., Satcher, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+high-surface-area+alumina+aerogels+without+the+use+of+alkoxide+precursors.">Synthesis of high-surface-area alumina aerogels without the use of alkoxide precursors.</a> Chem. Mater. 17, 395-401 (2005).</li><li>Bruno, B. A., Anderson, A. M., Carroll, M. K., Brockmann, P., Swanton, T., Ramphal, I. A., Palace, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Benchtop+Scale+Testing+of+Aerogel+Catalysts.">Benchtop Scale Testing of Aerogel Catalysts.</a> SAE Technical Paper 2016-01-920. , (2016).</li><li>Anderson, A. M., Wattley, C. W., Carroll, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Silica+Aerogels+Prepared+via+Rapid+Supercritical+Extraction:+Effect+of+Process+Variables+on+Aerogel+Properties.">Silica Aerogels Prepared via Rapid Supercritical Extraction: Effect of Process Variables on Aerogel Properties.</a> J. Non-Cryst. Solids. 355 (2), 101-108 (2009).</li></ol>

The authors have nothing to disclose.

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-precursors with aluminum salts, and incorporation of metal-containing nanoparticles into silica aerogels. When the wet gel pores contain only alcohol and water (i.e. silica protocols), solvent exchange is not required. In that case, the liquid precursor mixture can be poured directly into the metal mold, with gelation and extraction both occurring during the hot-press process, as demonstrated previously in Carroll et al.17 and in this protocol for Si-Cu NP aerogels. We use a somewhat longer hot press process to ensure gelation occurs in the mold prior to extraction. In this approach, a recipe that would gel under ambient conditions in &#60;4 h is desirable. Alternately, the RSCE method can be used to extract solvent from pre-gelled monolithic samples6,11 or smaller pieces of gel, as in the Si-Cu IMP, Al-Cu IMP and Al-Cu CoP sol gels in this protocol.
As noted in previous publications16,17, appropriately setting the restraining force supplied to the metal mold is very important to successful RSCE; this force must be adjusted depending on the mold size and shape. Each hot press has a maximum restraining force, which will limit the achievable volume of aerogel per extraction. Gels and solvents suitable for the RSCE process are limited to those that can withstand the temperature and pressure (T/P) conditions employed and do not react with either the metal mold or gasket materials. In addition, the T/P conditions must bring the solvent(s) in the gel above the critical point, or collapsed gels will be formed rather than aerogels. Because of the lack of shrinkage in the RSCE process, open-bottom molds are used to fabricate monoliths. Sealing an open-bottom mold is required to prevent leakage of precursor mixture onto the hot press platens. A closed-bottom mold is recommended for ease of use if intact monoliths are not needed for the end application.
Approaches in which nanoparticles are included in the precursor mixture for a base-catalyzed reaction of silica alkoxide precursors yield monolithic aerogels in a process that requires only 8 h from mixing the chemicals to removal of the aerogels from the mold10,17. This is considerably shorter than the total time of preparation of aerogels by supercritical CO2 extraction (including gel formation, solvent exchanges over a multiple-day period, processing). The processing time can be shortened to as little as 3 h by increasing the heating and cooling rates employed in the hot press program24. Use of an impregnation approach, as in the Al-Cu IMP gels demonstrated in this protocol, requires at least one solvent exchange, and thereby lengthens the overall time needed for aerogel fabrication. The epoxide-assisted method for preparing gels from salts22 requires multiple solvent exchanges prior to processing, in order to remove excess epoxide and byproducts of the reaction6. Consequently, although the time needed for mixing and gelation is short (&#60; 1 h) and RSCE can be accomplished in 5 h, the overall time for making the alumina-based aerogels described in this protocol is extended over several days.
Although this protocol has focused on the preparation of copper-containing aerogels, these methods can be used to incorporate a wide variety of metal-containing species, including nanoparticles, into alumina- or silica-based aerogels7,8,9. When employing suspensions of nanoparticles, settling of the nanoparticles within the precursor mixture may result in non-uniform distribution in the resulting aerogel material. Moreover, variations in colors of materials obtained in a single batch of aerogel indicate that subtle changes in conditions are sometimes experienced by a gel during processing, for example, in different positions within the metal mold. In the case of copper-containing species, significant changes in copper oxidation state and ligand structure occur during processing10,11, which merits further study.
The UCAT system23 allows for testing of catalytic aerogels under conditions that approximate those encountered in an automotive catalytic converter without requiring laboratory use of an automobile and sophisticated, expensive commercial test equipment. The cost of construction of UCAT was approximately $75k. Detection is limited to those gases detectable by the five-gas analyzer (CO, CO2, NO, O2, HCs), which does not provide a complete assessment of reaction products. When operated under the conditions demonstrated in this protocol, catalyst performance under reducing and oxidizing conditions can be assessed. Ongoing work focuses on adding capabilities to UCAT to permit testing under more varied conditions, including humidification and transient exhaust mixtures.

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.remotexs.ntu.edu.sg/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 (Figure 2a) appear red to green-gray in color11. Al-Cu CoP aerogels (not shown) are green to green-gray in color. Si-Cu IMP aerogels have a mottled appearance, with red, yellow and green colors observed (Figure 2b). Si-Cu NP aerogels are monolithic with colors that vary with weight percent of nanoparticle and also vary from well to well in the mold, indicating some variation in processing conditions experienced at different locations in the mold.10 For example, Si-Cu NP aerogel monoliths prepared from the Cu+2 dispersion at 3 wt%, and processed in the same batch, are yellow, purple, pink (Figure 2c) and green (not shown).
Table 7 lists representative physical characteristics of the as-prepared copper-containing aerogels. For the Si-Cu NP aerogels the surface area decreases as the weight percent of nanoparticles increases, as described in Anderson et al.10
Evidence of entrapment of copper in the aerogels is shown in the SEM/EDX images of Figure 3 and the XRD patterns of Figure 4. Figures 3a and 3b show SEM/EDX images of the Si-Cu NP aerogel prepared using the Cu+2 nanodispersion. A ca. 400-nm-diameter nanoparticle containing copper is shown, indicating that some agglomeration of the 25- to 55-nm nanoparticles in the original nanodispersion has occurred. Figure 3c shows smaller (ca. 50 nm) nanoparticles dispersed in the Al-Cu IMP aerogel.
The XRD patterns of the as-prepared Si-Cu IMP and Si-Cu NP aerogels (Figure 4, lower traces) contain peaks corresponding to metallic copper at 2&#952; = 43, 50 and 74&#176;, indicating that alcohothermal reduction of the copper species occurred during RSCE processing of the gels10,11. The as-prepared Al-Cu IMP aerogel pattern (Figure 4, top trace) shows XRD peaks consistent with the pseudoboehmite form of alumina and a copper(II)-containing species11. After heat treatment above 700 &#176;C, all of these copper-containing aerogels have XRD peaks (not shown) indicative of copper(II) oxide10,11.
The data in Figure 5 show that the copper-containing alumina aerogels are capable of catalyzing reactions that can eliminate each of the three major pollutants of concern in gasoline engine exhaust (CO, NO, and HCs) under the conditions tested11. Figure 6 demonstrates the catalytic ability in copper-containing silica aerogels10,11 and thereby provides evidence that the catalytic capabilities of metal-doped aerogels are robust (i.e. activity is demonstrated with the active copper species included in more than one aerogel matrix) and tailorable. The catalytic activity appears to depend on the details of the copper (speciation, particle size, loading level, etc.), how copper is introduced to the aerogel (impregnation, co-precursor, doping with copper nanoparticles) and the underlying aerogel itself (i.e. silica vs. alumina). The details of how these parameters and interactions affect catalytic performance are not yet well understood, but they do indicate that there is a significant &#34;design space&#34; for tailoring aerogel catalysts to specific functions, and that this is a rich area for future work. Further discussion of these results can be found in previously published work10,11,23.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Aerogel</td>
			<td>Density (g/mL)</td>
			<td>Surface Area (m2/g)</td>
		</tr>
		<tr>
			<td>Cu-Si Imp</td>
			<td>0.11</td>
			<td>780 &#177; 50</td>
		</tr>
		<tr>
			<td>Cu-Al Imp</td>
			<td>0.09 - 0.11</td>
			<td>390 - 430</td>
		</tr>
		<tr>
			<td>Si-Cu NP</td>
			<td>0.08 - 0.10</td>
			<td>200 - 500&#160;</td>
		</tr>
	</tbody>
</table>
Table 7. Representative Physical Characterization Data for the As-prepared Aerogels.
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/57075/57075fig2.jpg" /> 
Figure 2. Photographic images of copper-containing aerogels. (a) Al-Cu IMP; (b) Si-Cu IMP; (c) Si-Cu NP (made from 3 wt% Cu+2). Note that variations in color occur within aerogels fabricated in the same batch. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57075/57075fig2large.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/57075/57075fig3.jpg" /> 
Figure 3. SEM micrographs of as-prepared aerogels. (a) EDX backscattering image of 3 Si-Cu NP (made from 3 wt% Cu+2) (scale bar in bottom right corner: 800 nm); (b) EDX image of Cu signal for sample as in (a) (scale bar in bottom right corner: 800 nm); (c) SEM image of Al-Cu IMP aerogel (scale bar in bottom left corner: 200 nm). All images taken at 50kX magnification. Figures 3a and 3b have been reprinted from Anderson et al.10 Figure 3c has been reprinted from Tobin et al.11 <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57075/57075fig3large.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/57075/57075fig4.jpg" /> 
Figure 4. XRD patterns of as-prepared aerogels. The Al-Cu IMP aerogel shows evidence of pseudoboehmite (B) and crystals of a copper(II) salt (X). Both types of Si-Cu aerogels (IMP and NP) show evidence of metallic copper (Cu). Note the x-axis scale represents reflected beam for data collected using a copper X-ray source tube; y-axis scale not indicated because patterns are offset for clarity. This figure has been modified from Anderson et al.10 and Tobin et al.11 <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57075/57075fig4large.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/57075/57075fig5.jpg" /> 
Figure 5. Conversion of HCs, NO and CO for a copper-containing alumina aerogel prepared via the impregnation method. (a) In the absence of oxygen (300 ppm NO, 0.5% CO, 6.0% CO2 200 ppm propane for HC) and (b) in the presence of oxygen (0.36% O2, 295 ppm NO, 0.49% CO, 5.9% CO2 197 ppm propane for HC). Tests were performed using a space velocity of 20 s-1. Error bars represent the standard deviation in five runs. Lines are included as an aid to the eye. Shaded regions (pink for NO, green-brown for CO on left; blue for HC and green-gray for CO on right) indicate the conversion activity measured for an inert (silica) aerogel. This figure is reprinted from Tobin et al.11 <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/57075/57075fig5large.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/57075/57075fig6.jpg" /> 
Figure 6. Conversion of NO and CO for copper-nanoparticle-doped silica aerogels. (a) In the absence of oxygen (300 ppm NO, 0.5% CO, 6.0% CO2 200 ppm propane for HC) and (b) in the presence of oxygen (0.36% O2, 295 ppm NO, 0.49% CO, 5.9% CO2 197 ppm propane for HC). Tests were performed using a space velocity of 20 s-1.Three different types of nanoparticles were employed (Cu0, Cu+1, Cu+2) with weight percent as noted in legend. Data for unmodified silica aerogel and Si-Cu IMP aerogels are also included from Tobin et al.11 for comparison. Error bars represent the standard deviation of 2 or 3 runs. Lines are included as an aid to the eye. This figure is reprinted from Anderson et al.10

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 ...

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7.2K Views.  Union College. 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.

Video: Fabrication and Testing of Catalytic Aerogels Prepared Via Rapid Supercritical Extraction

Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method

A procedure for the fabrication of monolithic silica aerogels in eight hours or less via a rapid supercritical extraction process is described. The procedure requires 15-20 min of preparation time, during which a liquid precursor mixture is prepared and poured into wells of a metal mold that is placed between the platens of a hydraulic hot press, followed by several hours of processing within the hot press. The precursor solution consists of a 1.0:12.0:3.6:3.5 x 10-3 molar ratio of tetramethylorthosilicate (TMOS):methanol:water:ammonia. In each well of the mold, a porous silica sol-gel matrix forms. As the temperature of the mold and its contents is increased, the pressure within the mold rises. After the temperature/pressure conditions surpass the supercritical point for the solvent within the pores of the matrix (in this case, a methanol/water mixture), the supercritical fluid is released, and monolithic aerogel remains within the wells of the mold. With the mold used in this procedure, cylindrical monoliths of 2.2 cm diameter and 1.9 cm height are produced. Aerogels formed by this rapid method have comparable properties (low bulk and skeletal density, high surface area, mesoporous morphology) to those prepared by other methods that involve either additional reaction steps or solvent extractions (lengthier processes that generate more chemical waste).The rapid supercritical extraction method can also be applied to the fabrication of aerogels based on other precursor recipes.

This article describes a rapid supercritical extraction method for fabricating silica aerogels. By utilizing a confined mold and hydraulic hot press, monolithic aerogels can be made in eight hours or less.

A procedure for the fabrication of monolithic silica aerogels in eight hours or less via a rapid supercritical extraction process is described. The ...

Synthesis and Catalytic Performance of Gold Intercalated in the Walls of Mesoporous Silica

As a promising catalytically active nano reactor, gold nanoparticles intercalated in mesoporous silica (GMS) were successfully synthesized and properties of the materials were investigated. We used a one pot sol-gel approach to intercalate gold nano particles in the walls of mesoporous silica. To start with the synthesis, P123 was used as template to form micelles. Then TESPTS was used as a surface modification agent to intercalate gold nano particles. Following this process, TEOS was added in as a silica source which underwent a polymerization process in acid environment. After hydrothermal processing and calcination, the final product was acquired. Several techniques were utilized to characterize the porosity, morphology and structure of the gold intercalated mesoporous silica. The results showed a stable structure of mesoporous silica after gold intercalation. Through the oxidation of benzyl alcohol as a benchmark reaction, the GMS materials showed high selectivity and recyclability.

Here, we present a protocol with a sol-gel process to synthesize gold intercalated in the walls of mesoporous materials (GMS), which is confirmed to possess a mesoporous matrix with gold intercalated in the walls imparting great stability and recyclability.

As a promising catalytically active nano reactor, gold nanoparticles intercalated in mesoporous silica (GMS) were successfully synthesized and properties ...

Supercritical Nitrogen Processing for the Purification of Reactive Porous Materials

Supercritical fluid extraction and drying methods are well established in numerous applications for the synthesis and processing of porous materials. Herein, nitrogen is presented as a novel supercritical drying fluid for specialized applications such as in the processing of reactive porous materials, where carbon dioxide and other fluids are not appropriate due to their higher chemical reactivity. Nitrogen exhibits similar physical properties in the near-critical region of its phase diagram as compared to carbon dioxide: a widely tunable density up to ~1 g ml-1, modest critical pressure (3.4 MPa), and small molecular diameter of ~3.6 &#197;. The key to achieving a high solvation power of nitrogen is to apply a processing temperature in the range of 80-150 K, where the density of nitrogen is an order of magnitude higher than at similar pressures near ambient temperature. The detailed solvation properties of nitrogen, and especially its selectivity, across a wide range of common target species of extraction still require further investigation. Herein we describe a protocol for the supercritical nitrogen processing of porous magnesium borohydride.

Nitrogen is an effective supercritical fluid for extraction or drying processes due to its small molecular size, high density in the near-liquid supercritical regime, and chemical inertness. We present a supercritical nitrogen drying protocol for the purification treatment of reactive, porous materials.

Supercritical fluid extraction and drying methods are well established in numerous applications for the synthesis and processing of porous materials. ...

Preparation of Biopolymer Aerogels Using Green Solvents

Although the first reports on aerogels made by Kistler1 in the 1930s dealt with aerogels from both inorganic oxides (silica and others) and biopolymers (gelatin, agar, cellulose), only recently have biomasses been recognized as an abundant source of chemically diverse macromolecules for functional aerogel materials. Biopolymer aerogels (pectin, alginate, chitosan, cellulose, etc.) exhibit both specific inheritable functions of starting biopolymers and distinctive features of aerogels (80-99% porosity and specific surface up to 800 m2/g). This synergy of properties makes biopolymer aerogels promising candidates for a wide gamut of applications such as thermal insulation, tissue engineering and regenerative medicine, drug delivery systems, functional foods, catalysts, adsorbents and sensors. This work demonstrates the use of pressurized carbon dioxide (5 MPa) for the ionic cross linking of amidated pectin into hydrogels. Initially a biopolymer/salt dispersion is prepared in water. Under pressurized CO2 conditions, the pH of the biopolymer solution is lowered to 3 which releases the crosslinking cations from the salt to bind with the biopolymer yielding hydrogels. Solvent exchange to ethanol and further supercritical CO2 drying (10 - 12 MPa) yield aerogels. Obtained aerogels are ultra-porous with low density (as low as 0.02 g/cm3), high specific surface area (350 - 500 m2/g) and pore volume (3 - 7 cm3/g for pore sizes less than 150 nm).

A new way for the production of biopolymer-based aerogels by carbon dioxide (CO2) induced gelation is shown. The technique utilizes pressurized carbon dioxide (5 MPa) for the production of biopolymer hydrogels and supercritical CO2 (12 MPa) to convert gels into aerogels. The only solvents needed besides CO2 are water and ethanol.

Although the first reports on aerogels made by Kistler1 in the 1930s dealt with aerogels from both inorganic oxides (silica and others) and biopolymers ...

Laboratory Production of Biofuels and Biochemicals from a Rapeseed Oil through Catalytic Cracking Conversion

The work is based on a reported study which investigates the processability of canola oil (bio-feed) in the presence of bitumen-derived heavy gas oil (HGO) for production of transportation fuels through a fluid catalytic cracking (FCC) route. Cracking experiments are performed with a fully automated reaction unit at a fixed weight hourly space velocity (WHSV) of 8 hr-1, 490-530 &#176;C, and catalyst/oil ratios of 4-12 g/g. When a feed is in contact with catalyst in the fluid-bed reactor, cracking takes place generating gaseous, liquid, and solid products. The vapor produced is condensed and collected in a liquid receiver at -15 &#176;C. The non-condensable effluent is first directed to a vessel and is sent, after homogenization, to an on-line gas chromatograph (GC) for refinery gas analysis. The coke deposited on the catalyst is determined in situ by burning the spent catalyst in air at high temperatures. Levels of CO2 are measured quantitatively via an infrared (IR) cell, and are converted to coke yield. Liquid samples in the receivers are analyzed by GC for simulated distillation to determine the amounts in different boiling ranges, i.e., IBP-221 &#176;C (gasoline), 221-343 &#176;C (light cycle oil), and 343 &#176;C+ (heavy cycle oil). Cracking of a feed containing canola oil generates water, which appears at the bottom of a liquid receiver and on its inner wall. Recovery of water on the wall is achieved through washing with methanol followed by Karl Fischer titration for water content. Basic results reported include conversion (the portion of the feed converted to gas and liquid product with a boiling point below 221 &#176;C, coke, and water, if present) and yields of dry gas (H2-C2's, CO, and CO2), liquefied petroleum gas (C3-C4), gasoline, light cycle oil, heavy cycle oil, coke, and water, if present.

This paper presents an experimental method to produce biofuels and biochemicals from canola oil mixed with a fossil-based feed in the presence of a catalyst at mild temperatures. Gaseous, liquid, and solid products from a reaction unit are quantified and characterized. Conversion and individual product yields are calculated and reported.

The work is based on a reported study which investigates the processability of canola oil (bio-feed) in the presence of bitumen-derived heavy gas oil ...

A Simple and Efficient Protocol for the Catalytic Insertion Polymerization of Functional Norbornenes

Norbornene can be polymerized by a variety of mechanisms, including insertion polymerization whereby the double bond is polymerized and the bicyclic nature of the monomer is conserved. The resulting polymer, polynorbornene, has a very high glass transition temperature, Tg, and interesting optical and electrical properties. However, the polymerization of functional norbornenes by this mechanism is complicated by the fact that the endo substituted norbornene monomer has, in general, a very low reactivity. Furthermore, the separation of the endo substituted monomer from the exo monomer is a tedious task. Here, we present a simple protocol for the polymerization of substituted norbornenes (endo:exo ca. 80:20) bearing either a carboxylic acid or a pendant double bond. The process does not require that both isomers be separated, and proceeds with low catalyst loadings (0.01 to 0.02 mol%). The polymer bearing pendant double bonds can be further transformed in high yield, to afford a polymer bearing pendant epoxy groups. These simple procedures can be applied to prepare polynorbornenes with a variety of functional groups, such as esters, alcohols, imides, double bonds, carboxylic acids, bromo-alkyls, aldehydes and anhydrides.

We describe the catalytic insertion polymerization of 5-norbornene-2-carboxylic acid and 5-vinyl-2-norbornene to form functional polymers with a very high glass transition temperature.

Norbornene can be polymerized by a variety of mechanisms, including insertion polymerization whereby the double bond is polymerized and the bicyclic ...

Fabrication and Testing of Photonic Thermometers

In recent years, a push for developing novel silicon photonic devices for telecommunications has generated a vast knowledge base that is now being leveraged for developing sophisticated photonic sensors. Silicon photonic sensors seek to exploit the strong confinement of light in nano-waveguides to transduce changes in physical state to changes in resonance frequency. In the case of thermometry, the thermo-optic coefficient, i.e., changes in refractive index due to temperature, causes the resonant frequency of the photonic device such as a Bragg grating to drift with temperature. We are developing a suite of photonic devices that leverage recent advances in telecom compatible light sources to fabricate cost-effective photonic temperature sensors, which can be deployed in a wide variety of settings ranging from controlled laboratory conditions, to the noisy environment of a factory floor or a residence. In this manuscript, we detail our protocol for the fabrication and testing of photonic thermometers.

We describe the process of fabrication and testing of photonic thermometers.

In recent years, a push for developing novel silicon photonic devices for telecommunications has generated a vast knowledge base that is now being ...

Chemical Precipitation Method for the Synthesis of Nb2O5 Modified Bulk Nickel Catalysts with High Specific Surface Area

We demonstrate a method for the synthesis of NixNb1-xO catalysts with sponge-like and fold-like nanostructures. By varying the Nb:Ni ratio, a series of NixNb1-xO nanoparticles with different atomic compositions (x = 0.03, 0.08, 0.15, and 0.20) have been prepared by chemical precipitation. These NixNb1-xO catalysts are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The study revealed the sponge-like and fold-like appearance of Ni0.97Nb0.03O and Ni0.92Nb0.08O on the NiO surface, and the larger surface area of these NixNb1-xO catalysts, compared with the bulk NiO. Maximum surface area of 173 m2/g can be obtained for Ni0.92Nb0.08O catalysts. In addition, the catalytic hydroconversion of lignin-derived compounds using the synthesized Ni0.92Nb0.08O catalysts have been investigated.

Chemical Precipitation Method for the Synthesis of Nb2O5 Modified Bulk Nickel Catalysts with High Specific Surface Area

A protocol for the synthesis of sponge-like and fold-like Ni1-xNbxO nanoparticles by chemical precipitation is presented.

We demonstrate a method for the synthesis of NixNb1-xO catalysts with sponge-like and fold-like nanostructures. By varying the Nb:Ni ratio, a series of ...

A Rapid Synthesis Method for Au, Pd, and Pt Aerogels Via Direct Solution-Based Reduction

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various precursor noble metal ions with reducing agents in a 1:1 (v/v) ratio results in the formation of metal gels within seconds to minutes compared to much longer synthesis times for other techniques such as sol-gel. Conducting the reduction step in a microcentrifuge tube or small volume conical tube facilitates a proposed nucleation, growth, densification, fusion, equilibration model for gel formation, with final gel geometry smaller than the initial reaction volume. This method takes advantage of the vigorous hydrogen gas evolution as a by-product of the reduction step, and as a consequence of reagent concentrations. The solvent accessible specific surface area is determined with both electrochemical impedance spectroscopy and cyclic voltammetry. After rinsing and freeze drying, the resulting aerogel structure is examined with scanning electron microscopy, X-ray diffractometry, and nitrogen gas adsorption. The synthesis method and characterization techniques result in a close correspondence of aerogel ligament sizes. This synthesis method for noble metal aerogels demonstrates that high specific surface area monoliths may be achieved with a rapid and direct reduction approach.

A rapid, direct solution-based reduction synthesis method to obtain Au, Pd, and Pt aerogels is presented.

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various ...

Synthesis Method for Cellulose Nanofiber Biotemplated Palladium Composite Aerogels

Here, a method to synthesize cellulose nanofiber biotemplated palladium composite aerogels is presented. Noble metal aerogel synthesis methods often result in fragile aerogels with poor shape control. The use of carboxymethylated cellulose nanofibers (CNFs) to form a covalently bonded hydrogel allows for the reduction of metal ions such as palladium on the CNFs with control over both nanostructure and macroscopic aerogel monolith shape after supercritical drying. Crosslinking the carboxymethylated cellulose nanofibers is achieved using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) in the presence of ethylenediamine. The CNF hydrogels maintain their shape throughout synthesis steps including covalent crosslinking, equilibration with precursor ions, metal reduction with high concentration reducing agent, rinsing in water, ethanol solvent exchange, and CO2 supercritical drying. Varying the precursor palladium ion concentration allows for control over the metal content in the final aerogel composite through a direct ion chemical reduction rather than relying on the relatively slow coalescence of pre-formed nanoparticles used in other sol-gel techniques. With diffusion as the basis to introduce and remove chemical species into and out of the hydrogel, this method is suitable for smaller bulk geometries and thin films. Characterization of the cellulose nanofiber-palladium composite aerogels with scanning electron microscopy, X-ray diffractometry, thermal gravimetric analysis, nitrogen gas adsorption, electrochemical impedance spectroscopy, and cyclic voltammetry indicates a high surface area, metallized palladium porous structure.

A synthesis method for cellulose nanofiber biotemplated palladium composite aerogels is presented.The resulting composite aerogel materials offer potential for catalysis, sensing, and hydrogen gas storage applications.

Here, a method to synthesize cellulose nanofiber biotemplated palladium composite aerogels is presented. Noble metal aerogel synthesis methods often ...