Facet-Dependent of Catalytic Selectivity: The Case of H2O2 Direct Synthesis on Pd Surfaces

Pd catalysts display excellent potential applications in H2O2 direct synthesis from H-2 and O-2. Facet dependence on catalytic selectivity for H2O2 direct synthesis on Pd surfaces is investigated by the combination of DFT calculations and microkinetic study. It is found that the coadsorbed O plays a key role in catalytic activity and selectivity for H2O2 direct synthesis on Pd(111) and Pd(100) surfaces. The coadsorbed O on Pd surfaces could not only increase the catalytic activity but also promote the catalytic selectivity on Pd surfaces. With the help of coadsorbed O, Pd(111) surface shows a very high selectivity (>99%) for H2O2 products, but Pd(100) surface displays a high selectivity (>99%) for H2O formation. The role of proton transfer is also investigated in H2O2 direct synthesis, and it is found that proton transfer reactions are harmful to H2O2 formation. This work sheds light on the reaction mechanism of H2O2 direct synthesis reaction on different Pd surfaces, and it may create a new path to understand the facet-dependent on catalytic selectivity.