Carbon deposition on Ni-based catalyst with TiO2 as additive during the syngas methanation process in a fluidized bed reactor

Syngas methanation is a crucial step in industry to produce synthetic natural gas, but the Ni-based catalysts for this reaction often deactivate severely because of carbon formation. Tests were carried out in a pressurized fluidized bed methanation reactor in order to analyze the carbon deposition on the nickel-based methanation catalysts with TiO2 as additive (Ni-Ti/Al2O3) and a conventional Ni-based catalyst (Ni/Al2O3). Test results showed that Ni-Ti/Al2O3 performed better compared to Ni/Al2O3. At higher operating temperature (823 K), CO conversion on Ni-Ti/Al2O3 was 13.6% higher than that on Ni/Al2O3, CH4 yield was 39.7% higher and CH4 selectivity was even 64.7% higher for Ni-Ti/Al2O3 compared to Ni/Al2O3. The raw and spent catalysts were characterized with XRD, EDS and N-2 adsorption-desorption measurements to describe the carbon deposits on them. The characterization results indicated that elemental carbon appeared on the surface of the catalysts after methanation reaction and with the increase in reaction temperature, the carbon deposition was getting more serious. The deposited carbon blocked the tiny porous channels of the catalysts and caused a drastic change in the surface topography, which led to the degradation of the catalysts' performance. The TiO2 additive provided a physical barrier to hydrocarbon adsorption and decomposition on the catalyst surface and the oxygen vacancies on Ni-Ti/Al2O3 acted as the active sites to promote the removal carbon on the Ni particles. Thus, the TiO2 additive can enhance the anti-coking properties and catalytic activity of Ni-Ti/Al2O3 compared to Ni/Al2O3. These findings aid in further improvement and optimization of highly carbon-resistant catalysts.