Name: Fabrication and Testing of Catalytic Aerogels Prepared Via Rapid Supercritical Extraction (Video) | JoVE Journal
Uploaded: 2018-08-31T12:30:00.000+00:00
Duration: 9 min 28 s
Description: Learn to fabricate and test catalytic aerogels using rapid supercritical extraction with copper-doped silica and alumina platforms. This method enables quick preparation of high-performing materials for three-way automotive catalysis without precious metals.

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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.

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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-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 ("test section"), 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 ˚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 ("bypass") flow; from these data the "percent conversion" 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's design and functioning are presented in Bruno et al.23
<img alt="Thermal management system diagram; heat exchanger, PID heater, gas analyzer, data acquisition setup." class="xfigimg" src="/files/ftp_upload/57075/57075fig1.jpg" data-altupdatedat="1788250015000" data-alt="Figure 1"> 
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><tbody><tr><td>Variable micropipettor, 100-1000 &amp;micro;L</td><td>Manufactured by Eppendorf, purchased from Fisher Scientific www.fishersci.com</td><td>S304665</td><td>Any 100-1000 &amp;micro;L pipettor is suitable.</td></tr><tr><td>Variable Pipettor, 2.5-10 mL</td><td>Manufactured by Eppendorf, purchased from Fisher Scientific www.fishersci.com</td><td>21-379-25</td><td>Any variable pipettor is suitable.</td></tr><tr><td>Pasteur pipettes</td><td>FisherScientific</td><td>13-678-6A</td><td></td></tr><tr><td>Syringe</td><td>Purchased from Fisher Scientific</td><td>Z181390 syringe with Z261297 needle</td><td></td></tr><tr><td>Digital balance</td><td>OHaus Explorer Pro</td><td></td><td>Any digital balance is suitable.</td></tr><tr><td>Beakers</td><td>Purchased from Fisher Scientific</td><td></td><td>Any glass beaker is suitable.</td></tr><tr><td>Graduated Cylinder</td><td>Purchased from Fisher Scientific</td><td></td><td>Any glass graduated cylinder is suitable.</td></tr><tr><td>Magnetic Plate/Stirrer</td><td>FisherScientific Isotemp</td><td>SP88854200P</td><td>Any magnetic plate/stirrer is suitable.</td></tr><tr><td>Ultrasonic Cleaner</td><td>FisherScientific FS6</td><td>153356</td><td>Any sonicator is suitable.</td></tr><tr><td>Mold</td><td>Fabricated in House</td><td></td><td>Fabricate from cold-rolled steel or stainless steel.</td></tr><tr><td>Hydraulic Hot Press</td><td>Tetrahedron www.tetrahedronassociates.com</td><td>MTP-14</td><td>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><td>UCAT (Union Catalytic Testbed)</td><td>Fabricated in House</td><td></td><td>Described in detail in reference #21:&amp;nbsp; 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><td>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

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...

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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Learn to fabricate and test catalytic aerogels using rapid supercritical extraction with copper-doped silica and alumina platforms. This method enables quick preparation of high-performing materials for three-way automotive catalysis without precious metals.

Fabrication and Testing of Catalytic Aerogels Prepared Via Rapid Supercritical Extraction

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