Nickel oxide doped noble metals supported catalysts for carbon dioxide methanation and desulfurization reactions

Abstract

Malaysia has one of the most extensive natural gas pipeline networks in Asia. Using pipeline system, the gas will be channelled to the onshore station where the natural gas will undergo separation of acidic gases. Nowadays, the removal of toxic gases such as H2S and CO2 via chemical conversion attracted many researchers due to the effectiveness of the technique. In this research, new catalysts of high industrial impact that can catalyze the reactions of CO2 methanation and H2S desulfurization were developed. A series of catalysts based on nickel oxide doped with ruthenium, rhodium, palladium and platinum were prepared. Then, the best two catalysts were subjected to undergo several optimizations such as different calcination temperature of catalysts, calcinations temperature of alumina, different support materials, preparation method, reproducibility testing and regeneration testing. Pd/Ru/Ni (2:8:90)/Al2O3 and Rh/Ni (30:70)/Al2O3 catalysts exhibited the most potential catalysts resulted from the activity testing monitored by FTIR and GC. These catalysts were prepared using wetness impregnation technique, aging at 85oC and followed by calcination at 400oC. Both catalysts achieved 100% H2S desulfurization below 200oC. In the presence of H2S gas, only 3.64% CH4 was produced over Pd/Ru/Ni (2:8:90)/Al2O3 catalyst from 57.31% CO2 conversion, while 0.5% CH4 was obtained from 4.53% CO2 conversion over Rh/Ni (30:70)/Al2O3 at temperature of 400oC, respectively. However, the methane percentage increased to 39.73% for Pd/Ru/Ni (2:8:90)/Al2O3 catalyst from 52.95% CO2 conversion and 70.75% for Rh/Ni (30:70)/Al2O3 catalyst from 90.1% CO2 conversion during testing without flowing of H2S gas. Moreover, the XRD diffractogram showed that both catalysts are highly amorphous in structure with BET surface area in the range of 220-270 m2g-1. FESEM analysis indicated a rough surface morphology and non-homogeneous spherical shape with the smallest particles size in the range 40-115 nm for fresh Pd/Ru/Ni (2:8:90)/Al2O3 catalyst and formation of aggregates with rough surface morphology for fresh Rh/Ni (30:70)/Al2O3 catalyst. The elemental analysis performed by EDX confirmed the presence of Ni, Ru, Pd, Al and O in the Pd/Ru/Ni (2:8:90)/Al2O3 catalyst while, Ni, Rh, Al and O in the Rh/Ni (30:70)/Al2O3 catalyst. Characterization by FTIR and TGA-DTG revealed the existence of nitrate and hydroxyl ions on the catalysts surface.