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

The water-gas shift (WGS) reaction in the temperature range of 100-350 oC for various feed composi-tions simulating forward, reverse and real WGS conditions was studied for a series of coprecipitated mixed metal oxidecatalysts of 30 wt% of CuO and 70 wt% of metal oxide (CeO2, ZnO, Cr2O3, and ZrO2) as well as for a commercialWGS catalyst (ICI 83-3). The catalysts were characterized using BET, XRD, H2-TPR and N2O dissociation studies. Among the tested catalysts, CuO-Cr2O3 showed the best activity in the forward WGS, while the commercial catalystwas the best catalyst in the real and reverse WGS reactions. The effect of Cu content in the catalyst was also studiedand, in the case of the real WGS, 50 wt% CuO-Cr2O3 was more active than 30 wt% CuO-Cr2O3. H2 and CO2 were foundto inhibit the forward WGS, decreasing the reaction rate substantially, particularly at temperatures below 200 oC. Theinhibition effect varied depending on the tested catalyst and increased with increasing H2 or CO2 concentration. Asthe inhibition effect was reversible, the competitive adsorption of H2 or CO2 on the active sites has been suggested tobe responsible for the effect. The high activity of the commercial catalyst in the H2 rich real WGS could be describedby the difference in the H2 inhibition between the catalysts. An easily reducible copper species was found in CuO-Cr2O3and could be attributed to the high activity in the forward WGS.