Water-gas shift reaction over CuO/CeO_2 catalysts: Effect of CeO_2 supports previously prepared by precipitation with different precipitants

摘要

A series of CeO_2 supports were firstly prepared by precipitation method with NH_3-H_2O (NH), (NH_4)_2CO_3 (NC) and K_2CO_3 (KC) as precipitant, respectively, and then CuO/CeO_2 catalysts were fabricated by depositing CuO on the as-obtained CeO_2 supports by deposition-precipitation method. The effect of CeO_2 supports prepared from different precipitants on the catalytic performance, physical and chemical properties of CuO/CeO_2 catalysts was investigated with the aid of XRD, N_2-physisorption, N_O chemisorption, FT-IR, TG, H_2-TPR, CO_2-TPD and cyclic voltammetry (CV) characterizations. The CuO/CeO_2 catalysts were examined with respect to their catalytic performance for the water-gas shift reaction, and their catalytic activities and stabilities are ranked as: CuO/CeO_2 - NH > CuO/ CeO_2-NC > CuO/CeO_2-KC. Correlating to the characteristic results, it is found that the CeO_2 support prepared by precipitation with NH_3-H_2O as precipitant (I.e., CeO_2 - NH-300) has the best thermal stability and least surface "carbonate-like" species, which make the corresponding CuO/CeO_2- NH catalyst presents the highest Cu-dispersion, the highest microstrain (I.e., the highest surface energy) of CuO, the strongest reducibility and the weakest basicity. While, the precipitants that contain CO_3~(2-) (e.g. (NH_4)_2CO_3 and K_2CO_3) result in more surface "carbonate-like" species of CeO_2 supports and CuO/CeO_2 catalysts. As a result, CuO/CeO_2-NC and CuO/CeO_2-KC catalysts present poor catalytic performance.