CHARACTERIZATION BY INFRARED AND X-RAY ABSORPTION SPECTROSCOPY OF Ru/TiO2 CATALYSTS FOR CO2 METHANATION

This thesis investigates Ru/TiO2 catalysts for CO2 methanation, a critical reaction for CO2 recycling and reducing greenhouse gas emissions that converts CO2 and hydrogen (H2) into methane (CH4). Among various catalysts, Ru/TiO2 has proven to be highly effective due to strong metal-support interactions that enhance Ru dispersion and thermal stability. This study employs a multi-technique approach using Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy, X-ray Absorption Spectroscopy (XAS), and Mass Spectrometry (MS) to monitor the catalytic process operando. The primary objectives are to elucidate the reaction mechanism and to evaluate the impact of structural changes, particularly the restructuring of TiOx on Ru nanoparticles. Two different reaction protocols were tested, showing that structural variations induced by the reductive treatment in the Ru active sites significantly influence catalyst performance. The results reveal that the principal mechanism of reaction is the dissociative pathway and that at 260°C, Ru nanoparticles are fully reduced and tend to grow, enhancing both selectivity and methane yield. However, when the reductive treatment is performed at 140°C TiOx restructuring happens. These findings provide valuable insights into the mechanistic aspects of CO2 methanation and contribute to optimizing Ru/TiO2 catalysts for more efficient CO2 conversion.