One pot sol-gel synthesis of Pt−Ni/TiO2 with high CO2 methanation catalytic activity at low temperature

Abstract

In this work, 2 wt%Pt/TiO2, 20 wt%Ni/TiO2 monometallic catalysts and xwt%Pt−20 wt%Ni/TiO2 (x = 1, 2 and 4 wt%) bimetallic catalysts were synthesized by one-pot sol-gel method for CO2 methanation reaction. All bimetallic catalysts revealed higher CO2 conversion than both monometallic catalysts. The 2 wt%Pt−20 wt%Ni/TiO2 catalyst exhibited the highest percentage of CO2 conversion at low reaction temperature, with almost 100% CH4 selectivity and high stability during 72 h time on stream. The effect of Pt co-doped with Ni to bimetallic formed on the catalyst properties was studied using several techniques, including X-ray diffraction, N2 adsorption-desorption, Raman spectroscopy, transmission electron microscopy, field emission scanning electron microscopy, H2 temperature-programmed desorption, H2 temperature-programmed reduction, CO2 temperature-programmed desorption and X-ray absorption spectroscopy (both ex-situ and in-situ experiments). The results showed that Pt was dispersed on the catalyst surface in the form of platinum oxide, while Ni was both incorporated into the TiO2 lattice with the excess amount from saturated level being dispersed on the catalyst surface. The results from XAS evidenced that some electrons movement from Ni to Pt occurred. This electronic property changing can tune the interaction between Ni and TiO2 support with appropriate strength and then resulting in higher reducibility of the catalyst and higher dispersion of Ni species. Furthermore, the electron-rich Pt site on the catalyst surface favored to adsorb CO from CO2 dissociation and further activated adsorbed CO to interact with nearby hydrogen atoms to form CH4 leading to high CO2 methanation activity at low temperature.