Simultaneous impregnation of Ni and an additive via one-step melt-infiltration: Effect of alkaline-earth metal (Ca, Mg, Sr, and Ba) addition on Ni/γ-Al2O3 for CO2 methanation

As part of carbon energy recycling, the CO2 methanation process in the power to gas technology, which converts the electricity grid into a gas grid [CO2 + 4H(2) (produced by surplus electricity) -> CH4] using a catalytic process, has been developed in the countries such as Germany and Denmark. To achieve an efficient catalytic process, the design of low-cost and high-efficiency catalysts is required. In this study, highly loaded Ni/Al2O3 catalysts (30 wt %) were prepared using the alkaline-earth metals (Mg, Ca, Sr, and Ba) via one-step melt-infiltration (OSMI) method. The Ni active sites were investigated, and the effectiveness of each alkaline-earth metal (Ca, Mg, Sr, and Ba) was determined. The catalytic activity was investigated in the temperature range of 275-400 degrees C and weight gas hourly velocity (WHSV) of 160,000 mL.g(cat)(-1).h(-1) under atmospheric pressure. Ni and alkaline-earth metals were uniformly dispersed into the pore structure of the alumina support. The average metallic Ni particle size of each catalyst was similar (similar to 11 nm), and no severe Ni sintering was observed even at a Ni loading of 30 wt%. Mg-promoted Ni/Al2O3 catalyst was unsuitable for the OSMI method because the reduction of the Ni active sites was not completely accomplished at 400 degrees C. Ca-promoted Ni/Al2O3 catalyst afforded the best catalytic activity among other metal-promoted Ni/Al2O3 catalysts. Ca increased the CO2 adsorption amount and reducibility of the Ni active sites, and the optimum Ca loading was 5 wt%. However, the over-loading of Ca (10 wt%) was harmful to the catalytic activity of the Ni active sites.