Differences in Deterioration Behaviors of Cu/ZnO/Al 2 O 3 Catalysts with Different Cu Contents toward Hydrogenation of CO and CO 2 .

The deterioration behaviors of Cu/ZnO/Al 2 O 3 (CZA) catalysts upon different Cu contents were elucidated. The fresh and spent catalysts after being used in CO and CO 2 hydrogenation at 250 °C under atmospheric pressure were properly characterized using various techniques including X-ray powder diffraction, X-ray photoelectron spectroscopy, and temperature-programmed reduction for the changes of metal sites, while the textural and chemical properties and carbon deposition on spent CZA catalysts were analyzed by N 2 physisorption, energy-dispersive X-ray spectroscopy, and temperature-programmed oxidation. During the hydrogenation reaction for both CO and CO 2 , the unstable Cu 0 site on the spent CZA catalyst having a low Cu loading (sCZA-L) was oxidized to CuO and the aggregation of metal crystallite sites (Cu-ZnO and ZnO) was observed. Moreover, the amount of carbon deposition on sCZA-L (ca. >2%) is higher than the spent CZA catalyst having a high Cu loading (sCZA-H, ca. <0.5%). These phenomena led to a decrease in the surface area and the blockage of active sites. These findings can be determined on the catalytic deactivation and the obvious decrease in the catalytic activity of the CZA catalyst having a low Cu content (CZA-L, Cu:Zn = 0.8).