Effect of Carbon Dioxide on the Activity of Pd–Pt Bimetallic Catalysts During Partial Oxidation of Methane Towards Enriched Hydrogen Production
摘要
Hydrogen production via catalytic partial oxidation of methane is a promising route for the direct use of renewable feedstock such as biogas. High-temperature partial oxidation is preferred for a higher hydrogen selectivity. The Pd-based catalysts undergo a deactivation phase transition by coke deposition between 625 and 725 °C, resulting in a significant drop in methane conversion. The strategies adapted to limit the coke deposition were (1) introduce an inert diluent and (2) use a suitable promoter to reduce the active metal particle size. In this study, Pd/γ-Al2O3 and Pd–Pt/γ-Al2O3 catalysts were synthesized using wetness impregnation and characterized for morphology, crystallography, and surface chemistry. The catalysts’ performance was studied in a quartz packed bed reactor between 625 and 725 °C, at a gas hourly space velocity of 36,800 ml/(gcat.hr), and a CH4:CO2:O2 ratio of 1:0.5:0.5. The maximum methane and carbon dioxide conversion was 64% and 49% for Pd–Pt/γ-Al2O3 and 48% and 36% for Pd/γ-Al2O3 at 725 °C. The drop in methane conversion was not observed in the Pd–Pt/γ-Al2O3 catalyst. The hydrogen selectivity was 85% and 90% for the Pd/γ-Al2O3 and the Pd–Pt/γ-Al2O3, respectively, at 725 °C. The enhanced performance of Pd–Pt/γ-Al2O3 is attributed to the presence of the Pd–Pt alloy, smaller active particles, and higher dispersion evident from the morphological and electronic configuration studies. Though the amount of coke is higher for the Pd–Pt/γ-Al2O3, it has a lower graphitization and is easy to remove. These findings make the Pd–Pt/γ-Al2O3 a potential catalyst for the enhanced hydrogen production from biogas partial oxidation without feedstock separation.