Interaction between Pd and ZnO during Reduction of Pd/ZnO Catalyst for Steam Reforming of Methanol to Hydrogen

The changes in catalyst structure and species and charge transfer during the reduction of a co-precipitated Pd/ZnO catalyst with 15.9% Pd loading were studied by TPR, TPD, temperature-programmed electronic conductivity, and XRD. The effect of reduction temperature on the catalytic performance in steam reforming of methanol was measured. Metallic palladium was highly dispersed on ZnO. The strong interaction between Pd and ZnO during the catalyst reduction with hydrogen led to hydrogen spillover from Pd to ZnO, which caused the reduction of ZnO close to the metallic palladium and the formation of PdZn alloy. The presence of metallic palladium facilitated the reduction of ZnO and formation of a PdZn alloy, which was the active species for the methanol conversion. The catalysts with a PdZn alloy crystallite size of 5-14 nm that were obtained by reduction at 523-573 K showed the best catalytic performance. The methanol conversion was 41%, CO₂ selectivity 94%, and hydrogen yield 0.65 mole/g-hr at 523 K and 17.2/hr over 15.9% Pd/ZnO pre-reduced at 573 K.