Modulation of Selectivity and Activity of Ni/TiO₂ Catalysts by Metal Dispersion in Photothermal CO₂ Hydrogenation

Abstract

Ni/TiO2 catalysts are efficient and cost‐effective for photothermal CO2 hydrogenation. However, the achieved CO/CH4 ratio strongly depends on the specific characteristics of these catalysts. To further ascertain the role of metal dispersion and photoactivation on selectivity, in this work we investigate the impact of Ni loading over high surface area anatase on the photothermal performance. Catalysts with 3 and 10 wt. % of Ni prepared by incipient wetness impregnation show initial good dispersion of the metal, although after activation in H2 metallic Ni nanoparticles are observed for 10%Ni/TiO2. This last catalyst demonstrates superior CO2 hydrogenation activity at high temperature, but below 200 ºC it is overpassed by the catalyst with 3 wt % Ni/TiO2. The selectivity varies remarkably with Ni loadings. Thus, at 350 °C about 93 % of methane is obtained over 10 wt.% Ni/TiO2, while 3%Ni/TiO2 yields about 97 % of CO. Low‐intensity UV irradiation enhances performance, particularly at temperatures below 200 ºC, where an increment in the production of methane of up to 75 % is observed for 3 wt.% Ni/TiO2 at 200 ºC. These results highlight the influence of metal dispersion, along with irradiation on modulating the selectivity of the photothermal CO2 hydrogenation