Methanol Synthesis Using CO₂ and H₂ on Nano Silver-Ceria Zirconia Catalysts: Influence of Preparation Method

Silver catalysts supported on ceria-zirconia (CZ) mechanically mixed oxide were synthesized by wet impregnation and chelating methods. Nominal loadings of 5 wt.% of Ag was deposited on the CZ support. These catalysts were tested for the CO₂ hydrogenation reaction to methanol with feed gas composition of CO₂-H₂ = 3:1 at 250 °C, 20 bar total pressure and GHSV of 1800 h^-1. The calcined and reduced catalysts were characterized using XRD, BET, TPR, SEM-EDS, XPS and FTIR-DRIFTs techniques. Finely deposited silver crystallites sized in the range of 20-50 nm were observed through SEM and HR-TEM analysis. TPR and XRD studies demonstrated the presence of Ag₂O and metallic silver (Ag⁰) on CZ support. About 10% of CO formation was observed on chelating catalyst (5Ag/CZ CHE). However, only, 5% CO was observed on impregnated (5Ag/CZ IMP) catalyst. The greater CO formation was associated with ease reduction of Ag₂O to metallic silver in 5Ag/CZ CHE catalyst. Further, 70% of methanol selectivity was observed on 5Ag/CZ IMP due to the presence of Ag₂O on CZ. FTIR-DRIFTs results revealed the methanol formation via formate intermediates and CO formation via RWGS reaction on the studied catalysts.