Preparation of Cu/Zno-Based Heterogeneous Catalysts by Photochemical Deposition, Their Characterization and Application for Methanol Synthesis from Carbon Dioxide and Hydrogen

Industry is changing rapidly and the energetic and environmental aspects have become two major concerns for several processes. To this effect, great efforts have been invested to converting the emitted CO₂ to useful chemicals and fuels. And the best choice would be reuse of CO₂ emission through conversion by methanol synthesis. Methanol is environment-friendly fuel compared to several other sources of energy. It is convenient fuel source for fuel cell application.

Drs. Pori, Likozar, Crnjak Orel from National Institute of Chemistry and Prof. Marjan Marinsek from University of Ljubljana in Slovania prepared Cu/ZnO-based heterogeneous catalysts by photochemical deposition and utilized it synthesis of methanol carbon dioxide and hydrogen. The research work appeared in the peer-reviewed journal, Electrochimica Acta.

Methanol can be produced from syngas, containing CO, CO₂ and H₂, over a ternary Cu/ZnO/Al₂O₃ catalysts, prepared with the co-precipitation method with sodium carbonate. Recently, methanol synthesis by CO₂ hydrogenation are widely accepted for research interest, due it effective way of activating and converting CO₂. When the conventional Cu-based catalyst is used for CO₂ hydrogenation to methanol, the methanol yield was much lower than that obtained from syngas under similar reaction conditions. It was later traced back to the deactivation of the Cu/ZnO/Al₂O₃ catalysts, which the team explained that the production of water as a byproduct, decreases the yield of methanol production.

The researchers developed a new preparation method for Cu/ZnO catalysts, and this is based on the photochemical deposition procedure of CuO on the previously prepared ZnO substrate. They investigated the activity and stability of CO₂ hydrogenation to methanol of the prepared catalysts, and some fundamental morphological factors controlling the stability and activity of the employed Cu-ZnO systems.

Researchers also confirmed that a neat ZnO is basically inactive toward the synthesis of methanol, while the rate of the methanol formation increases significantly when dispersed into two oxides, CuO and ZnO. Cu crystallite size of the commercial catalyst prepared by co-precipitation method is found to be lower when compared to those of the prepared catalysts. The Cu crystallites deposited on ZnO support are dispersed on the surface of ZnO support and consequently a large reactive surface area, accessible for reaction molecules is provided. Small size Cu crystallites are commonly highly dispersed over the surface of ZnO particles to cause a high overall surface area of the composites. The synthesized catalysts can be seen as the underlying mechanism for a higher stability of the catalysts, prepared by the employed photochemical method, H₂0 accumulates the pores of the available catalytic surface, thereby suppressing the production of methanol. Besides H₂O, CO suppresses the methanol synthesis over the Cu/ZnO-based catalysts, and the effect of H₂O was found to be much stronger than that of CO.

This study shows the preparation of the Cu/ZnO materials by photochemical method facilitates obtaining the catalysts with a higher activity towards methanol formation in comparison with those prepared using a conventional co-precipitation method. Preparing the catalysts with the photochemical method improved the catalytic stability by suppressing water and carbon monoxide formation.