Reactivity of Pd–Cu/Al2O3 and Cu/Al2O3 during catalytic hydrogen combustion – In-situ mechanistic study and rate law determination

Abstract

This study compares the performance, including reactivity and stability, of Pd–Cu/Al2O3 and Cu/Al2O3 catalysts during catalytic hydrogen combustion in a temperature range of 20–600 °C. The physicochemical and catalytic properties of catalysts were characterized using various analytical techniques. The reaction rates were measured using a fixed-bed reactor connected to a micro-gas chromatograph, and the rate law equations containing a term for steam partial pressure were determined. The effects of reaction temperature and catalyst composition on the reaction mechanism were investigated using in-situ Fourier-transform infrared spectroscopy analysis, and the generation of OH groups was analyzed to compare the reaction pathways of catalytic hydrogen combustion over Pd–Cu/Al2O3 and Cu/Al2O3 catalysts. The results showed that at temperatures above 500 °C, Cu/Al2O3 achieved a comparable hydrogen conversion (96.5 and 98%) to that of Pd–Cu/Al2O3. The rate-limiting steps of catalytic combustion over Pd–Cu/Al2O3 and Cu/Al2O3 were the formation and breaking of metal-oxygen bonding, respectively. It was also found that the difference between the reactivity of Pd–Cu/Al2O3 and Cu/Al2O3 was less pronounced under wet conditions.