Adsorption and Deactivation Characteristics of Cu/ZnO-Based Catalysts for Methanol Synthesis from Carbon Dioxide

The adsorption and deactivation characteristics of coprecipitated Cu/ZnO-based catalysts were examined and correlated to their performance in methanol synthesis from CO2 hydrogenation. The addition of Ga2O3 and Y2O3 promoters is shown to increase the Cu surface area and CO2/H-2 adsorption capacities of the catalysts and enhance methanol synthesis activity. Infrared studies showed that CO2 adsorbs spontaneously on these catalysts at room temperature as both mono- and bi-dentate carbonate species. These weakly bound species desorb completely from the catalyst surface by 200 A degrees C while other carbonate species persist up to 500 A degrees C. Characterization using N2O decomposition, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy with energy-dispersive X-ray spectroscopy analysis clearly indicated that Cu sintering is the main cause of catalyst deactivation. Ga and Y promotion improves the catalyst stability by suppressing the agglomeration of Cu and ZnO particles under pretreatment and reaction conditions.