Partial oxidation of methane over monometallic and bimetallic Ni-, Rh-, Re-based catalysts: Effects of Re addition, co-fed reactants and catalyst support

Abstract

Partial oxidation reactions of CH4 over monometallic Ni, Rh, Re and bimetallic Re-Ni catalysts supported by Al2O3 were studied at 400–700 °C. Among monometallic catalysts, Rh/Al2O3 exhibited the highest catalytic activity. Lower CH4 conversion and H2 yield were observed over Ni/Al2O3 catalyst, while Re/Al2O3 catalyst did not promote the reaction under the studied condition. Addition of Re over Ni to form a bimetallic catalyst considerably promoted the activity of Ni/Al2O3 catalyst, particularly at a higher temperature (600 °C). Re-Ni proportion was then optimized; Re-Ni/Al2O3 at Re:Ni ratio of 3:7 resulted in a significantly higher CH4 conversion as well as H2 and CO yields when compared to noble-metal Rh/Al2O3 catalyst. Stability testing of Re-Ni/Al2O3, Ni/Al2O3 and Rh/Al2O3 catalysts was also conducted. After 18-h operation, Re-Ni/Al2O3 catalyst still exhibited high stability with slight deactivation in terms of H2 yield, whereas Ni/Al2O3 and Rh/Al2O3 catalysts showed higher deactivation rates. Post-reaction temperature programmed oxidation confirmed the better resistance toward carbon deposition of Re-Ni/Al2O3 catalyst. The effect of steam and CO2 addition on the Re-Ni/Al2O3 catalyst performance was also investigated. The presence of a suitable H2O content could increase H2 and CO yields and reduce the amount of carbon deposition, whereas the presence of CO2 showed undesirable influence on the reaction by reducing CH4 conversion and H2/CO ratio. Lastly, Re-Ni/Gd-CeO2 catalyst was prepared and tested to study the effect of catalyst support. The catalyst stability and resistance toward carbon deposition were significantly improved, which could be due to the high oxygen storage capacity of Gd-CeO2.