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April 2014

Body Armor for Catalysts

Researchers demonstrate how overcoating catalysts enhances stability

James Gallagher

Researchers found that an aluminum oxide coating (blue spheres) improves a copper-based catalyst's survival rate in the harsh conditions involved in biofuel manufacturing. The research graced the cover of Angewandte Chemie International Edition. O'Neill, BJ, DHK Jackson, AJ Crisci, CA Farberow, F Shi, AC Alba-Rubio, J Lu, PJ Dietrich, X Gu, CL Marshall, PC Stair, JW Elam, JT Miller, FH Ribeiro, PM Voyles, J Greeley, M Mavrikakis, SL Scott, TF Kuech, and JA Dumesic. Stabilization of Copper Catalysts for Liquid-Phase Reactions by Atomic Layer Deposition. Angewandte Chemie International Edition. 2013 52 (13808-13812). Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission.

Covering the active surface of a catalyst with a non-active material seems like a crazy idea. It flies in the face of the conventional wisdom that good catalysts have as much of the active surface available as possible. However, James Dumesic and colleagues at the Institute for Atom-efficient Chemical Transformations (IACT) have discovered that such an approach leads to impressive improvements in catalyst stability while maintaining selectivity to the desired products.

The high-temperature, high-pressure liquid water conditions used to turn biomass into useful fuels and chemicals create a harsh environment for catalysts. Under these conditions, earth-abundant base metal catalysts have a tendency toward leaching and particle growth. This leads to irreversible catalyst deactivation that is costly and creates solid waste requiring disposal or reprocessing. The IACT researchers have found that an overcoating of relatively inert aluminum oxide on top of catalytic copper nanoparticles can prevent such deactivation and increase the stability of the catalysts.

This breakthrough allows inexpensive metals such as copper to be used in place of their expensive cousins, such as platinum, which are naturally more stable under the demanding reaction conditions. In turn, this may increase the viability of fuel and chemical production from renewable resources.

The overcoating method utilizes atomic layer deposition, a process that arranges films of atoms on the catalyst in a layer-by-layer manner. Initially, the whole catalytic surface is covered, but the IACT team discovered that when they heated the catalyst, tiny pores were created in the overcoat. These pores allowed the reactants to access the active copper sites where catalysis occurs, while the copper atoms susceptible to deactivation, typically located at corners and edges of the particles, were still covered and therefore stabilized. Importantly, the selectivity to the desired product of the reaction was unaffected.

Previously, IACT researchers used a similar method for stabilizing precious metal catalysts. From that study they found that the overcoat preferentially covered the corners and edges of the nanoparticles, which are the areas most likely to cause deactivation. IACT director and co-author Chris Marshall notes, “This program was started by IACT about two years ago and has blossomed into a major thrust area. We believe that we can improve catalyst stability and selectivity for a wide variety of catalytic processes by careful choice of the overcoat type, thickness, and pre-treatment.”

Efforts are now focused on understanding the precise nature of the porosity and investigation of other systems where the approach could be beneficial. “One of the first directions that we would like to explore is to change the acid-base properties of the stabilizing overcoat layer,” says Dumesic.

“It should be possible to design a bifunctional catalytic material that couples a metal-catalyzed reaction on the copper surface with an acid-catalyzed reaction within an acidic overcoat layer,” says Brandon O’Neill, the first author of the paper.

Acknowledgments

O’Neill et al.: This material is based upon work supported as part of IACT, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES). Electron microscopy and chemisorption/kinetics were supported by DOE, Office of BES. Nuclear magnetic resonance spectroscopy was supported by the National Science Foundation (NSF) under the Center for Enabling New Technologies through Catalysis and use of the Materials Research Laboratory was supported by the Materials Research Science and Engineering Center Program at NSF. Some computational work was performed using resources at Pacific Northwest National Laboratory and the National Energy Research Scientific Computing Center.

Lu et al.: JWE, JPG, BL, and JL were supported as part of IACT. ZF and MJB were supported by the Institute for Catalysis and Energy Processes (DOE). PCS and YL were supported by the DOE BES Hydrogen Fuel Initiative, Chemical Sciences. Use of the Center for Nanoscale Materials was supported by the DOE, Office of Science, BES. The authors also acknowledge grants of computer time from EMSL, a national scientific user facility at Pacific Northwest National Laboratory,the Argonne Laboratory Computing Resource Center, and resources at the National Energy Research Scientific Computing Center.

More Information

O'Neill, BJ, DHK Jackson, AJ Crisci, CA Farberow, F Shi, AC Alba-Rubio, J Lu, PJ Dietrich, X Gu, CL Marshall, PC Stair, JW Elam, JT Miller, FH Ribeiro, PM Voyles, J Greeley, M Mavrikakis, SL Scott, TF Kuech, and JA Dumesic. 2013. “Stabilization of Copper Catalysts for Liquid-Phase Reactions by Atomic Layer Deposition.” Angewandte Chemie International Edition 52(51):13808-13812. DOI: 10.1002/anie.201308245

Lu, J, B Liu, J Greeley, X Feng, J Libera, Y Lei, M Bedzyk, P Stair, and J Elam. 2012. “Porous Alumina Protective Coatings on Palladium Nanoparticles by Self-Poisoned Atomic Layer Deposition.” Chemistry of Materials 24(11):2047-2055. DOI: 10.1021/cm300203s

About the author(s):

Catalysts Courageous

Cloak shields copper atoms, letting catalyst work efficiently under harsh conditions

A copper-based catalyst's survival rate in the harsh conditions involved in biofuel manufacturing are improved by an aluminum oxide coating.

Creating fuels from plant matter or agricultural waste often requires high temperatures, extreme pressures, and water. The harsh conditions deactivate desirable catalysts. Scientists discovered that a relatively inert aluminum oxide coating improves a copper-based catalyst's survivability. The covering is layered, atom by atom, around the catalyst. When heated, pores form that let molecules enter the catalyst to react while maintaining the covering that protects the mobile copper atoms. The coating does not alter the catalyst's ability to generate the desired product. The research could allow abundant metals, such as copper, to be used instead of rare metals in biofuel production. Scientists at the Institute for Atom-efficient Chemical Transformations, led by Argonne National Laboratory, did the research and are now studying the porosity in detail and investigating other systems where the approach could be valuable.

More Information

O'Neill, BJ, DHK Jackson, AJ Crisci, CA Farberow, F Shi, AC Alba-Rubio, J Lu, PJ Dietrich, X Gu, CL Marshall, PC Stair, JW Elam, JT Miller, FH Ribeiro, PM Voyles, J Greeley, M Mavrikakis, SL Scott, TF Kuech, and JA Dumesic. 2013. “Stabilization of Copper Catalysts for Liquid-Phase Reactions by Atomic Layer Deposition.” Angewandte Chemie International Edition 52(51):13808-13812. DOI: 10.1002/anie.201308245

Lu, J, B Liu, J Greeley, X Feng, J Libera, Y Lei, M Bedzyk, P Stair, and J Elam. 2012. “Porous Alumina Protective Coatings on Palladium Nanoparticles by Self-Poisoned Atomic Layer Deposition.” Chemistry of Materials 24(11):2047-2055. DOI: 10.1021/cm300203s

Disclaimer: The opinions in this newsletter are those of the individual authors and do not represent the views or position of the Department of Energy.