Direct synthesis of dimethyl ether from CO2 hydrogenation over a highly active, selective and stable catalyst containing Cu–ZnO–Al2O3/Al–Zr(1 : 1)-SBA-15

Abstract

Aluminum and zirconium doped SBA-15 (Al–Zr(1 : 1)-SBA-15) mesoporous catalysts were prepared by an in situ hydrothermal method and physically mixed (1 : 1 ratio) with the Cu–ZnO–Al₂O₃ (CZA) catalyst for direct DME synthesis from CO₂ hydrogenation. The high metal incorporation in the SBA-15 (Si/M = 10; where M = Al + Zr) framework enhances the surface area and porosity. The other physiochemical properties and catalytic activity of the Al–Zr(1 : 1)-SBA-15 catalyst were analyzed by SAXS, WAXD, N₂ adsorption–desorption, TEM, SEM, EDX, XPS, CO₂-TPD, NH₃-TPD, FTIR, and ICP-OES. The optimum reaction conditions of DME synthesis from CO₂ are as follows: 240 °C, 3 MPa pressure, H₂/CO₂ = 3 and GHSV of 1500 mL g_cat⁻¹ h⁻¹. The catalyst was found to be stable during a 100 h TOS study and the CO₂ conversion and DME selectivity were only reduced to 19.06 from 22.5% and 69.56 from 73.07%, respectively, and the space time yield of DME (STY_DME) achieved was 160.25 g_DME h⁻¹ kg_cat⁻¹. It was found that methanol dehydration to DME synthesis followed both the Langmuir–Hinshelwood and Eley–Rideal mechanisms. The pathway is solely dependent on the availability of acidic and basic sites on the catalyst surface.