Effect of alkali metal auxiliary in HCHO oxidation on the model catalyst Na2O/Pd(1 1 1): A DFT study

Abstract Alkali metal over noble-metal based catalyst could significantly promote room-temperature HCHO oxidation. Understanding alkali metal auxiliary effects from a molecular level is vital for improving the design of the catalytic oxidation catalysts. The electronic interaction between Na2O and the Pd(1 1 1) surface and HCHO oxidation mechanism on these model catalysts have been investigated using periodic density functional theory (DFT) calculations. The results showed the Pd(1 1 1) are negatively charged after Na2O introduction derived from electron transfer between Na2O and Pd(1 1 1). The adsroption ability of Na2O/Pd(1 1 1) increased, resulting in the enhancement of the interactions between reactants and Pd-based catalyst. Furthermore, the possible reaction pathways for HCHO oxidation on the Pd(1 1 1) and Na2O/Pd(1 1 1) surface were also evaluated inorder to elucidate the role of alkali Na. The generation of dioxymethylene and formate intermediates is the only way for HCHO oxidation whether with or without Na2O auxiliary. Unlike on the pure Pd catalyst, the formate will directly decompose into CO2 via the modulation of alkali metal. The function of alkali-metal auxiliary is not only modulating the electronic state of primary catalyst, but also includes taking part in the actual reaction.