Insights into the mechanism of formic acid dehydrogenation on Pd-Co@Pd core-shell catalysts: A theoretical study

摘要

The decomposition mechanism of formic acid on three Pd-based core-shell catalysts PdxCoy@Pd(1 1 1) (x:y = 1:3, 1:1 and 3:1) and pure Pd(1 1 1) surfaces has been systematically studied by periodic density functional theory (DFT) calculations. The possible dehydrogenation and dehydration pathways through the HCOO, COOH and HCO intermediates have been identified. It is found that the most favorable dehydrogenation pathways on Pd1Co3@Pd(1 1 1) and PdCo@Pd(1 1 1) are the COOH-mediated pathway, which are different from the HCOO-mediated pathway on Pd3Co1@Pd(1 1 1) and Pd(1 1 1). The increase of Co content in the Pd-Co core inhibits HCOOH dehydrogenation, but promotes the H-H coupling to form H-2, and improves the anti-CO poisoning ability of the catalysts. Accordingly, three bimetallic PdxCoy@Pd catalysts exhibit better overall catalytic activity and product selectivity toward H-2 + CO2 than pure Pd(1 1 1), especially PdCo@Pd(1 1 1) has the best catalytic performance for HCOOH decomposition. The present calculations show that a suitable Co composition in Pd-Co core plays an important role in tuning the catalytic performance, which provides a theoretical guideline to design high performance bimetallic core-shell catalysts for other dehydrogenation reactions.