A Study of Support Effects for CH 4 and CO Oxidation over Pd Catalysts on ALD-Modified Al 2 O 3
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A Study of Support Effects for CH4 and CO Oxidation over Pd Catalysts on ALD-Modified Al2O3 Xinyu Mao1 · Alexandre Foucher2 · Eric A. Stach2 · Raymond J. Gorte1,2 Received: 22 January 2019 / Accepted: 30 January 2019 © Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract Interactions between a metal and its oxide support can influence CO and CH4 oxidation, but promotion by the support can be difficult to study because oxides can have different surface structures and surface areas. To focus on the chemical aspects of support promotion for CO and CH4 oxidation, this study investigated the effect of support composition on Pd catalysts by rO2 on γ-Al2O3 using Atomic Layer Deposition (ALD). preparing uniform films of NiO, C o3O4, Fe2O3, MnO2, CeO2, and Z The structure of the films was characterized by XRD and STEM, and catalysts with ~ 1-wt% Pd were examined for CO and CH4 oxidation. CeO2/γ-Al2O3 was unique among the supports in greatly stabilizing the Pd dispersion to 1173 K. Rates for CO oxidation were enhanced by the presence of C eO2, Fe2O3, and M nO2, while the other oxides had no promotional effect. For CH4 oxidation, only NiO and Co3O4 were modest promoters, while the other reducible oxides even showed a negative effect on rates. Possible reasons for the differences between CH4 and CO oxidation activities are discussed. Graphical Abstract
Keywords Methane oxidation · CO oxidation · Palladium · Support effects · Atomic Layer Deposition
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10562-019-02699-6) contains supplementary material, which is available to authorized users. * Raymond J. Gorte [email protected] 1
Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, USA
Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, USA
2
1 Introduction A primary challenge for emissions control from natural-gas engines is the difficulty of oxidizing CH4 and CO at lower temperatures, preferably below 623 K [1], in the presence of a high partial pressure of water. The catalyst must also be catalytically and mechanically stable under very harsh conditions, since they can experience temperatures above
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1273 K, conditions which can lead to sintering of both the metal and the support [2]. Better materials are still needed. CO oxidation over Pd catalysts is reasonably well understood, and the effect of metal-oxide/Pd interactions is clearly important. On non-interacting supports, the reaction is structure insensitive and rates are proportional to the exposed Pd surface area, limited by the rate of O 2 adsorption for higher CO:O2 ratios on the CO-saturated surface [3, 4]. With supports such as CeO2 that can transfer oxygen at the metaloxide/Pd interface, rates can be orders-of-magnitude higher than on Pd/Al2O3 [5]. The higher rates on Pd/CeO2 are due to an additional rate process, which has a lower activation energy a
