Slag-based geopolymer microspheres as a support for CO2 methanation

Abstract

Reducing the emission of CO2 and converting it into energy are the key issues researchers are concerned about. Geopolymers with the advantage of alkali metal synergistic catalysis and excellent ability to adsorb metals are promising catalyst supports. To prove this point, KOH-activated chemically synthesized slag (CaO-MgO-Al2O3-SiO2) and ground granulated blast furnace slag were used as the raw materials in this study to prepare CO2 methanation catalysts. Ni metal (15 wt%) was loaded onto the slag-based geopolymers using the incipient wetness impregnation method. The as-synthesized slag-based geopolymer and real slag-based geopolymer catalysts were prepared and denoted as Ni-P-SGS and Ni-S-SGS, respectively. The results showed that the Ni-P-SGS catalyst showed better Ni dispersion, more alkaline sites, and stronger CO2 adsorption capacity, and hence higher catalytic activity for CO2 methanation than the Ni-S-SGS catalyst. Therefore, the Ni-P-SGS catalyst showed a CO2 conversion of 80.2% and a CH4 selectivity of 99.2% at 400 °C/0.1 MPa and a weight hourly space velocity of 12000 mL g-−1h−1. This performance is superior to that of the Ni-S-SGS catalyst, which showed a CO2 conversion of 72.8% and CH4 selectivity of 98.3%. In addition, the hydrogenation of formate seemed to be the rate-limiting step for the formation of CH4. This work provides sufficient evidence that geopolymers are promising catalyst supports.