Spray-made Cu/CeO2 catalyst with aerosol-assited sol-gel method for CO2 hydrogenation into methanol

Details

Supervisors

Debecker, Damien P.

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en chimie et bioindustries, à finalité spécialisée

Abstract

The hydrogenation of CO2 to methanol represents a promising alternative for reducing greenhouse gas emissions through carbon capture and utilisation. Several catalysts have already been developed, but they have certain shortcomings, such as thermodynamic limitations, low selectivity or water-accelerated deactivation. The aim of this final-year dissertation is to develop a Cu/CeO2 catalyst prepared using the aerosol-assisted sol-gel (AASG) method. Various supports were compared (CeO2, SiO2, Al2O3), as well as two dopants (Ga and Zn). An initial series of catalysts was prepared by wet impregnation (WI) on different supports; subsequently, the best support (CeO2) was synthesised via the aerosol method, along with a reference catalyst (AER-Cu/SiO2). The results obtained are surprising: the ceria-supported catalyst (AER-CuZn/CeO2) synthesised by aerosol, despite its high specific surface area (145 m2/g instead of 32 m2/g) and high dispersion, did not perform better than its counterpart prepared by WI. The catalyst that yielded the best results was WI-CuZn/CeO2 prepared by WI, with a selectivity exceeding 94% up to 240°C and a productivity of 0.32 mmol/g·h at 240°C. To explain this difference, a detailed characterisation (XRD, TEM, TPR, N2O chemisorption, CO2-TPD, DRIFTS) of these catalysts revealed that the copper particles formed by aerosol synthesis were 3 nm in size. This size falls below the optimal range of 5 to 8 nm, preventing the formation of the B5-type active sites required for efficient methanol synthesis, as well as being prone to oxidation. The copper particles in the catalyst synthesised by WI had a size of 40 nm. Although larger than the optimal range, they nevertheless allow for a better Cu0/Cu+ balance to be maintained. Various calcination temperatures (up to 650°C) were tested in an attempt to sinter the copper particles and achieve a particle size greater than 3 nm, but these tests did not yield conclusive results. Although the WI-CuZn/CeO2 outperforms its aerosol-synthesised counterpart, much research can still be carried out on the subject to improve its performance, particularly to successfully control sintering and achieve an optimal nanoparticle size.