Nickel oxide based catalysts for the simultaneous reactions of methanation and desulfurization

Abstract

Malaysian crude natural gas is categorized as a sour gas due to the contamination of carbon dioxide (CO2) and hydrogen sulfide (H2S). Recently, the removal of these sour gases via chemical conversion technique becomes the most promising technique. The objective of this novel catalyst development is to achieve both low temperature and high conversion of sour gases to be applicable in gas industry. The advantage of catalytic technology is the utilization of CO2 present in the production of methane gas. Supported mixed metal oxide catalysts were prepared by wetness impregnation method for the in-situ reactions of H2S desulfurization and CO2 methanation from ambient temperature up to 300oC. Fe/ Co/ Ni (10: 30: 60)-Al2O3 and Pr/ Co/ Ni (5: 35: 60)-Al2O3 catalysts were revealed as the most potential resulted from the catalytic activity screening by Fourier Transform Infrared Spectroscopy (FTIR) and Gas Chromatography (GC). Results showed that the conversion of H2S to elemental sulfur over the catalysts was achieved 100% even around 250oC. Methanation of CO2 in the presence of H2S yielded 2.9% of CH4 over Fe/ Co/ Ni (10: 30: 60)-Al2O3 catalyst and 6.1% of CH4 over Pr/ Co/ Ni (5: 35: 60)- Al2O3 catalyst at maximum studied temperature of 300oC. X-ray Photoelectron Spectroscopy (XPS) revealed Ni2O3 and Fe3O4 as the surface active components on the Fe/ Co/ Ni (10: 30: 60)-Al2O3 catalyst, while Ni2O3 and Co3O4 on the Pr/ Co/ Ni (5: 35: 60)-Al2O3 catalyst. X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscope (FESEM) showed that the supported catalysts are amorphous in structure. Results from Energy Dispersive X-ray Analysis (EDX) indicated the presence of 2.7% and 0.9% of sulfur on the spent Fe/ Co/ Ni (10: 30: 60)-Al2O3 and Pr/ Co/ Ni (5: 35: 60)-Al2O3 catalysts, respectively. There was 5.5% reduction of surface area over the spent Fe/ Co/ Ni (10: 30: 60)-Al2O3 catalyst characterized by Nitrogen Adsorption analysis. Meanwhile, there was 8.6% increment of surface area over the spent Pr/ Co/ Ni (5: 35: 60)-Al2O3 catalyst, which would explain the dramatic increased of catalytic performance over this catalyst at maximum studied temperature of 300oC. Characterization by FTIR and Thermogravimetry Analysis- Differential Thermal Analysis (TGA-DTA) revealed the existence of residue of nitrate and surface hydroxyl compounds on the catalysts. The aim to obtain high H2S desulfurization rate at low temperature was achieved. However, improvement is still needed for the CO2 methanation reaction at low temperature in the presence of H2S