CO2 Hydrogenation to Methanol with Ga- and Zn-Doped Mesoporous Cu/SiO2 Catalysts Prepared by the Aerosol-Assisted Sol-Gel Process

The preparation of copper-based heterogeneous catalysts dedicated to the hydrogenation of CO2 to methanol typically relies on multi-step procedures carried out in batch. These steps are precisely tailored to introduce the active phase (Cu) and the promoters (e.g. zinc, gallium) onto a preformed support, to maximize catalyst performance. However, each process step – often carried out in batch – can be associated with the formation of waste and with the consumption of energy, thereby negatively impacting the environmental performance of the overall catalyst preparation procedure. Here, we propose a direct and continuous production process for the synthesis of efficient catalysts for the CO2 to methanol reaction. Gallium- and zinc-promoted mesoporous Cu-SiO2 catalysts are prepared in one step by the aerosol-assisted sol-gel process. The catalysts consist of spherical microparticles and feature high specific surface area and pore volume, with interconnected pores of about 6 nm. A strong promoting effect of Ga and Zn is highlighted, boosting the selectivity for methanol at the expense of CO. Upon calcination, we show that Cu species – initially trapped in the silica matrix – undergo a migration towards the catalyst surface and a progressive sintering. After optimization, the catalysts obtained via such direct route compete with the best catalysts reported in the literature and obtained via multi-step approaches.