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Oxygenate Reactions over PdCu and PdAg Catalysts: Distinguishing Electronic and Geometric Effects on Reactivity and Selectivity

preprint
revised on 09.10.2020 and posted on 09.10.2020 by Tanmayi Bathena, Truc Phung, Scott Svadlenak, Yu Liu, Lars Grabow, Konstantinos A Goulas
We investigate PdCu and PdAg catalysts in the context of oxygenate upgrading for biofuels. To this end, we measure the rates of decarbonylation and hydrogenation of butyraldehyde, the reactive intermediate for the industrially relevant Guerbet condensation, and correlate the selectivity and reactivity with the properties of the catalysts via a range of characterization efforts. Data obtained from EXAFS and XANES show that the bulk of the catalyst metallic nanoparticles is enriched in Pd, while the surface is enriched in Cu and Ag. The data for PdCu show clear dominance of geometric (ensemble) effects on the selectivity. Conversely, the electronic (ligand) effects of alloying dominate over the reaction rate of the catalysts, as electron donation from Cu to Pd promotes the Cu and increases the desired (de)hydrogenation reactions. In contrast, in PdAg catalysts, the weaker electronic exchange, as indicated by Pd L edge XANES and theoretical calculations, is not sufficient to promote Ag, resulting in monotonic loss of activity with increasing Ag content and without selectivity improvement. We use the implications of these findings to provide valuable design principles for oxygenate catalysis and to discover a highly selective bifunctional catalyst system, comprised of a PdCu alloy catalyst and titanium dioxide for the upgrading of ethanol to longer-chain oxygenates.

Funding

CAREER: Theory-guided design of a novel chemical looping process for methane coupling using hydrogen storage materials

Directorate for Engineering

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MRI: Acquisition of a High Resolution Field Emission Transmission Electron Microscope at Oregon State University

Directorate for Mathematical & Physical Sciences

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MRI: Acquisition of a High Performance Computing System for Science and Engineering Research and Education at the University of Houston

Directorate for Computer & Information Science & Engineering

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DE-AC02-06CH11357

History

Email Address of Submitting Author

goulask@oregonstate.edu

Institution

Oregon State University

Country

United States

ORCID For Submitting Author

0000-0001-8306-2888

Declaration of Conflict of Interest

No conflict of interest.

Version Notes

First version of manuscript

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