CO2 methanation on Mg-doped Ni-Cu/Co modified mesoporous SiO2 derived from rice husks.

Mesoporous silica (SiO₂) was prepared using a simple procedure from rice husks without the application of a template. Incipient wetness impregnation method was employed to prepare magnesium-doped nickel-copper- and nickel-cobalt-containing SiO₂ catalysts. The obtained materials were characterized by X-ray powder diffraction (XRD), N₂ physisorption, transmission electron microscopy (TEM), temperature-programmed reduction (TPR-TGA), and NMR and XPS spectroscopies. The study demonstrated the significant influence of Ni and Co/Cu content, as well as the sequence of Mg promotion (before or after the nickel-copper- and nickel-cobalt-modification) on the physico-chemical properties of the catalysts. The peculiar properties of the mesoporous carrier positively influenced the formation of finely dispersed nickel and/or copper/cobalt oxide species, which were readily reducible at temperatures below 600 °C. XPS analysis revealed that the surface of Mg-doped Ni-Co supported SiO₂ catalysts was rich in nickel. All the prepared catalysts were active in CO₂ hydrogenation to methane. The Mg-doped Ni-Co supported SiO₂ catalysts showed higher catalytic activity compared to their Mg-doped Ni-Cu counterparts. The 1.5Mg10Ni5Co/SiO₂ catalyst demonstrated 82% CO₂ conversion and 99.5% selectivity to methane. The activity and selectivity of this catalyst was maintained at 400 °C for a reaction time of 4 h.