Comparison of CuO-MO_x (M=Ce, Zn, Cr and Zr) catalysts in various water-gas shift reactions

摘要

The water-gas shift (WGS) reaction in the temperature range of 100-350 ℃ for various feed compositions simulating forward, reverse and real WGS conditions was studied for a series of coprecipitated mixed metal oxide catalysts of 30 wt% of CuO and 70 wt% of metal oxide (CeO_2, ZnO, Cr_2O_3, and ZrO_2) as well as for a commercial WGS catalyst (ICI 83-3). The catalysts were characterized using BET, XRD, H_2-TPR and N_2O dissociation studies. Among the tested catalysts, CuO-Cr_2O_3 showed the best activity in the forward WGS, while the commercial catalyst was the best catalyst in the real and reverse WGS reactions. The effect of Cu content in the catalyst was also studied and, in the case of the real WGS, 50 wt% CuO-Cr_2O_3 was more active than 30 wt% CuO-Cr_2O_3. H_2 and CO_2 were found to inhibit the forward WGS, decreasing the reaction rate substantially, particularly at temperatures below 200 ℃. The inhibition effect varied depending on the tested catalyst and increased with increasing H_2 or CO_2 concentration. As the inhibition effect was reversible, the competitive adsorption of H_2 or CO_2 on the active sites has been suggested to be responsible for the effect. The high activity of the commercial catalyst in the H_2 rich real WGS could be described by the difference in the H_2 inhibition between the catalysts. An easily reducible copper species was found in CuO-Cr_2O_3 and could be attributed to the high activity in the forward WGS.