Tailoring Rh content on dendritic fibrous silica alumina catalyst for enhanced CO2 capture in catalytic CO2 methanation

Abstract

Dendritic fibrous X%Rh/FSA catalysts were synthesized by the microwave-assisted microemulsion and wetness impregnation approaches. Catalytic CO2 methanation was performed at temperature ranging of 150‒500 °C and atmospheric pressure with stoichiometric feed composition. FESEM and TEM micrographs confirmed the spherical bicontinuous concentric lamellar morphology of FSA offering high accessibility of capturing CO2 to the active sites, thus promotion of heterogenous catalysis activity. H2-TPR and pyrrole adsorbed IR spectroscopy results reveals that the metal-support interaction and degree of basicity strength were enormously enhanced with the increasing Rh content. The 1%Rh appeared to be the optimal loading with respect to the CO2 conversion and CH4 formation rate as a function of temperature, accredited to its medium basicity strength and fibrous morphology. The in situ FTIR analyses showed that medium basic sites promoted the desired carbonate species that readily participate into hydrogenation compared to strong basic sites. In addition, CH4/CO2 ratio indicates that the rate of CO hydrogenation was superior to that of RWGS over Rh/FSA catalysts. The absence of graphitic carbon for all spent Rh/FSA catalysts in post-characterization analyses suggests that their excellent catalytic performance could be assigned to the preservation of most active sites owing to enhanced CO2 adsorption on catalyst surface which effectively remove amorphous carbon deposits via CO2 gasification process.