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

• Published in: ACS catalysis 2022-05, Vol.12 (10), p.5766-5775
• Main Authors: Bathena, Tanmayi, Phung, Truc, Svadlenak, Scott R., Liu, Yu, Grabow, Lars C., Goulas, Konstantinos A.
• Format: Article
• Language: English
• ISSN: 2155-5435; 2155-5435
• DOI: 10.1021/acscatal.2c00561

We investigate Pd x Cu y /SiO2 and Pd x Ag y /SiO2 catalysts in the context of oxygenate upgrading for biofuels. To this end, we measure the rates of decarbonylation and hydrogenation of butyraldehyde and 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 Pd x Cu y /SiO2 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 Cu and increases the desired (de)­hydrogenation reactions. In contrast, in PdAg catalysts, the weaker electronic exchange, as indicated by Pd LIII XANES and theoretical calculations, is not sufficient to promote Ag, resulting in the monotonic loss of activity with the 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, comprising PdCu3/SiO2 and TiO2 for upgrading ethanol to longer-chain oxygenates.