Influence of Residual Chloride on CO and CO2 Adsorption and Selective Methanation Performance of Ru/Al2O3 Catalysts

CO-selective methanation (CO-SMET) has emerged as an effective approach for achieving deep CO removal in hydrogen-rich gases. Residual chloride (Cl−) plays a significant role in determining the CO removal performance of Ru/Al2O3 catalysts. In this study, a series of Ru/Al2O3 catalysts with different residual Cl− contents were prepared by performing 0–10 water-washing cycles on RuCl3-derived Ru/Al2O3. The catalysts’ CO and CO2 adsorption behaviors, as well as their CO-SMET performance, were systematically evaluated. The results show that within a residual Cl− content range of 140.2–32.4 μmol g−1, decreasing Cl− markedly increases the CO chemisorption capacity (from 0.028 to 0.048 mmol g−1), leading to significantly enhanced CO methanation under high CO coverage and a much lower minimum CO outlet concentration (from 59 to 3.3 ppm). In contrast, although CO2 chemisorption amount also increases (from 0.023 to 0.036 mmol/g) with decreasing Cl− content, no significant change in the CO2 methanation rate is observed below 280 °C due to inhibition of CO2 dissociation by adsorbed CO. Consequently, within the CO removal temperature window, reducing residual Cl− does not noticeably compromise CO selectivity. These findings provide new insights into the role of residual Cl− in CO-SMET over Ru/Al2O3 catalysts and suggest a rational strategy for improving CO removal depth while maintaining high CO selectivity.