The Performance of PdxAu1-X RCT-SiO2 for the Partial Oxidation of Alcohols: Effects of Molecular Weight and Operating Temperature on Selectivity and Conversion.

Recently, selective oxidation of high-chain alcohols on nanoporous silver-gold alloy catalysts (npAgAu) has been studied using a reaction network method which accurately predicted the reactivity and selectivity in a flow reactor experiment¹. The generality of this network is yet to be applied to other gold-based alloy catalysts.

Here, we extend the method to investigate the selective oxidation of alcohols on dilute palladium-in-gold alloy nanoparticles supported on a “raspberry colloid templated” SiO₂ support² (Pd_xAu_1-x RCT-SiO₂). The catalysts were tested in a fixed-bed catalytic reactor at atmospheric pressure after an in situ oxygen treatment, followed by stabilization under reaction conditions at an elevated temperature. At 150°C the methanol conversion is nearly 100%, but C₂-C₄ alcohols show low conversion. Increasing the reactor temperature to 250°C increases the conversion of these alcohols to between 60 and 90% with high selectivity to form aldehydes. The product distribution and analysis of residual carbon indicate the importance of carboxylate intermediates that block the reaction at the lower temperature. Additional studies of CO oxidation were utilized to probe active sites of the Pd_xAu_1-x catalysts and their dynamic nature.

The results show broad similarities in mechanism on Pd_xAu_1-x RCT-SiO₂ to that observed on npAgAu, but the Pd based catalyst is more active. This similarity points to the generality of the utility of the dilute alloy catalysts for selective catalytic chemistry.

References

(1) Reece, C.; Luneau, M.; Friend, C. M.; Madix, R. J. Predicting a Dramatic Decline in Selectivity for Catalytic Esterification of Alcohols from van Der Waals Interactions. Angew. Chemie - Int. Ed. 2020, Accepted. https://doi.org/10.1002/anie.202001576.

(2) Luneau, M.; Shirman, T.; Filie, A.; Timoshenko, J.; Chen, W.; Trimpalis, A.; Flytzani-Stephanopoulos, M.; Kaxiras, E.; Frenkel, A. I.; Aizenberg, J.; et al. Dilute Pd/Au Alloy Nanoparticles Embedded in Colloid-Templated Porous SiO2: Stable Au-Based Oxidation Catalysts. Chem. Mater. 2019, 31, 5759–5768. https://doi.org/10.1021/acs.chemmater.9b01779.