The effect of CO on intermetallic PdZn/ZnO and Pd2Ga/Ga2O3 methanol steam reforming catalysts: A comparative study

The catalytic properties in methanol steam reforming (MSR) of PdZn/ZnO and Pd2Ga/Ga2O3 were investigated and related to the actual surface composition. MSR selectivities of around 90% were observed on both catalysts. In situ FTIR spectroscopy was utilized to clarify the origin of the CO formed as a by-product. Exposure to CO at room temperature caused a degradation of both intermetallic surfaces, which was more severe on Pd2Ga. Likely, the strong Pd–CO interaction led to enrichment of Pd at the surface, as observed by the CO spectra resembling that of CO on metallic Pd. A limited stability of the PdZn and Pd2Ga surfaces was also observed in methanol/water, most likely due to the CO formed as a by-product in MSR. Therefore, the surface under reaction conditions consists of domains of metallic Pd (or a Pd-rich alloy) in addition to the intermetallic surface. This effect was more pronounced at lower temperatures. A faster in situ regeneration of the intermetallic surface by the hydrogen produced in MSR at elevated temperatures (>500 K) is proposed. Degradation by CO and re-reformation of the alloy by H2 likely leads to a certain steady state of the surface. X-ray absorption spectroscopy measurements indicate that the effect of CO apparently goes beyond the surface only.