CREATION OF THE ACTIVE-SITE FOR METHANOL SYNTHESIS ON A CU SIO2 CATALYST/

The effect of ZnO/SiO2 in a physical mixture of Cu/SiO2 and ZnO/SiO2 o n methanol synthesis from CO2 and H-2 was studied to clarify the role of ZnO in Cu/ZnO-based catalysts. An active Cu/SiO2 was prepared by th e following procedure: the Cu/SiO2 and ZnO/SiO2 catalysts with a diffe rent SiO2 particle size were mixed and reduced with H-2 at 523-723 K, and the Cu/SiO2 was then separated from the mixture using a sieve. The methanol synthesis activity of the Cu/SiO2 catalyst increased with th e reduction temperature and was in fairly good agreement with that pre viously obtained for the physical mixture of Cu/SiO2 and ZnO/SiO2. The se results indicated that the active site for methanol synthesis was c reated on the Cu/SiO2 upon reduction of the physical mixture with H-2. It was also found that ZnO itself had no promotional effect on the me thanol synthesis activity except for the role of ZnO to create the act ive site. The active site created on the Cu/SiO2 catalyst was found no t to promote the formation of formate from CO2 and H-2 on the Cu surfa ce based on in situ FT-IR measurements. A special formate species unst able at 523 K with an OCO asymmetric peak at similar to 1585 cm(-1) wa s considered to be adsorbed on the active site.