Liquid phase methanol synthesis by CO₂ hydrogenation over Cu-Zn/Z catalysts: Influence of Cd promotion

Background: The current scenario of high CO₂ emissions, which is causing global warming and climate change, one of the greatest challenges faced by the global community. One of the most promising ways to recycle CO₂ and thus mitigate its emission into the natural environment is the catalytic conversion of CO₂ into valuable products such as methanol, hydrocarbons, dimethyl ether (DME), formaldehyde, syngas, alcohols and urea. Method: Zeolite supported Cu-Zn bimetallic (Cu-Zn/Z) catalysts were synthesized by co-precipitation method. The synthesized catalysts were doped with different concentration of Cd to investigate the promoting role of Cd. To investigate the physicochemical profile of the calcined Cu-Zn/Z nano-catalysts, various analytical techniques were used. Significant findings: Thermal stability of zeolite support was carried out using Thermogravimetric analysis (TGA). TGA data exhibited higher thermal stability of the zeolite support. XRD findings revealed highly dispersed Cd promoted Cu-Zn oxides on the surface of the zeolite support. Field Emission Scanning Electron Microscopy (FESEM) was used to investigate morphology, which indicated the nano size of synthesized catalysts with uniform distribution of metal oxides. Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) detected bulk composition of each metal. BET surface studies revealed the mesoporous nature of Cd promoted Cu-Zn/Z catalysts. X-ray Photoelectron Spectroscopy (XPS) revealed the surface chemistry of Cd promoted Cu-Zn/Z catalysts. Activity data showed the active profile of Cd promoted Cu-Zn/Z catalysts for CO₂ hydrogenation to methanol by accelerating the methanol synthesis rate from 73 to 157 g.meth/kg.cat.h. Structure-activity studies identified metal-support interactions and Cu stability as the main factors governing the three-phase methanol synthesis rate from CO₂ hydrogenation. The importance of Cd promotion was further demonstrated by the fact that activity profile revealed better performance of the current catalysts with recently reported data in the literature.