Silica/titania composite-supported Ni catalysts for CO methanation: Effects of Ti species on the activity, anti-sintering, and anti-coking properties

Abstract

Catalysts composed of Ni supported on SiO2/TiO2 composite oxides (ST) with different Si/Ti molar ratios have been prepared by an ultrasonic impregnation method and used in CO methanation. Experimental results show that the ST systems have large specific surface area, large pore volume, and offer suitable metal–support interactions, thereby facilitating the dispersion of Ni. Indeed, these catalysts have more suitable Ni active sites for methanation, and the composite oxides show good support and synergistic effects. Thus, Ni/STx (x=50, 10, 5, 1) with a Ni loading of 10wt% displayed higher catalytic performances relative to catalysts composed of Ni supported on individual oxides (SiO2, TiO2, and γ-Al2O3). Among the catalysts, 10Ni/ST5 displayed the best catalytic activity (370°C, CO conversion: 99.9%, CH4 selectivity: 95.6%). Furthermore, 10Ni/ST5 showed better CH4 yield (290°C, CH4 yield: 92.4%), anti-sintering properties (smaller Ni particles), and anti-coking properties (lower amount of deposited carbon) after a stability test of duration 144h at 600°C than those of a typical 10Ni/γ-Al2O3 catalyst (290°C, CH4 yield: 80.0%). This can be attributed to the optimal amount of TiO2 separating/separated from the ST5 and playing the role of an electronic promoter. It not only effectively facilitated the dispersion of Ni during sintering, but also triggered electron transfer and enhanced the electron cloud density of Ni00 (Ni00→Niδ−), thereby weakening the CO bond of Ni-CO and enhancing the dissociation of CO.