CO oxidative coupling to dimethyl oxalate over Pd monolayer supported on SiC substrate: insight into the effects of different exposed terminals

Abstract

Developing supported Pd-based catalysts with the low Pd amount and excellent catalytic performance is essential for CO oxidative coupling to dimethyl oxalate (DMO), where elucidating the effects of different exposed terminals of substrate materials on catalytic performance is crucial to the design of supported catalysts. Herein, Pd monolayer was supported on SiC with different exposed terminals, constructing the models of PdML/SiC(111)-Si and PdML/SiC(111)-C terminal, which was used to investigate the effects of different exposed terminals of substrate materials on DMO synthesis from CO and OCH3. The density functional theory (DFT) calculations illustrated there existed no difference in the optimum path to generate DMO, which was COOCH3-COOCH3 coupling path on two catalysts. However, the rate control steps of the optimum path were different, with 2COOCH3 → DMO on the PdML/SiC(111)-Si terminal and COOCH3 + (CO + OCH3) → 2COOCH3 on the PdML/SiC(111)-C terminal. The micro-reaction kinetic model analysis further showed that the catalytic performance of PdML/SiC(111)-Si terminal was favorable than that of PdML/SiC(111)-C terminal, mainly attributing to that the difference in the exposed terminals of substrate materials led to the different electrons transfer directions of the Pd monolayer, then changed the adsorption energy of reactants (CO, OCH3) and key intermediates (COOCH3, OCCOOCH3), and further changed rate control step of the optimum path. This work offers the insights in rational design of supported Pd-based catalyst for heterogeneous catalytic reaction.