Temperature Dependence of Solar Light Assisted CO₂ Reduction on Ni Based Photocatalyst

Abstract

Methanation of CO₂ by H₂ can be in the future an important reaction to store the surplus of renewable electricity during production peaks. The catalytic thermal CO₂ methanation (the Sabatier reaction) can be carried out at temperatures above 250 °C using Ni supported on silica-alumina (Ni/SiO₂–Al₂O₃). Recently it has been observed that this exothermic reaction can be promoted by solar light irradiation of Ni/SiO₂–Al₂O₃ at initial near ambient temperatures. In the present work we provide a study of the influence of the initial temperature on the photoassisted Ni/SiO₂–Al₂O₃ methanation of CO₂, under conditions in which the dark reaction is not observed. An increase of the photoassisted methanation rate with the initial temperature in the range from ambient to 150 °C has been observed. The reaction kinetics for lower initial temperatures exhibited an induction period not observed for reactions performed at higher temperatures. The results are discussed in terms of the operation of plasmon photo activation in which the energy of photons is thermalised in a confined space of the active nanoparticles leading to locally high temperatures and the simultaneous photogeneration of electrons and positive holes.