Catalytic properties of PdZn/ZnO in formic acid decomposition for hydrogen production

This is one of the first reports, which is related to hydrogen production through formic acid decomposition over Pd/ZnO catalysts widely used for methanol steam-reforming. These catalysts have been investigated in comparison with Pt/ZnO and Pd/Al₂O₃ catalysts as well as ZnO support. HAADF/STEM, XRD, XPS and DRIFTS in situ studies of the systems were performed. The measured catalyst activity corresponds to the following order: Pd/Al₂O₃≥Pd/ZnO > Pt/ZnO > ZnO. Among the studied catalysts, Pd/ZnO showed the highest selectivity to hydrogen (up to 99.3%). This was assigned to the formation of a PdZn alloy during the reductive pre-treatment of the catalyst. An increase of the pre-treatment temperature from 573 to 773 K led to a significant increase of the mean PdZn (PtZn) nanoparticle size. However, the catalyst activity did not change, but the selectivity to hydrogen increased. These features closely remind the behavior of Pd/ZnO catalysts in methanol steam reforming implying that the mechanism of formic acid decomposition involves the same key steps and active sites.