alumina; thermal stability; HT water gas shift catalyst
Alumina (Al2O3) was added as a component of conventional iron oxide based high temperature water gas shift (WGS) catalysts. The catalysts contained Fe-Al-Cr-Cu-O and were synthesized by coprecipitation. A series of catalysts were prepared with 5 to 50 wt% Al2O3, 8 wt% Cr2O3, 4 wt% CuO, and the balance Fe2O3. One catalyst was prepared in which the chromia was replaced by alumina. All of the catalysts were compared to a reference WGS catalyst (88 wt% FeOX, 8 wt% Cr2O3, and 4 wt% CuO) with no alumina. The catalysts were characterized using temperature programmed reduction (TPR), surface area analysis using nitrogen physisorption, and scanning electron microscopy (SEM) with compositional analysis. The catalysts were also tested kinetically under WGS conditions. Addition of 10 to 15 wt% alumina increased the catalyst activity and thermal stability, with approximately 15 wt% alumina addition being optimum, as this catalyst produced a reaction rate (normalized per mass) 74% higher than the reference catalyst. The effect of alumina addition was greater than the surface area increase alone, which suggests that alumina alters the activity of the iron oxide domains, likely through an increase in reducibility, as shown by the TPR results. This synergistic effect was only observed when both alumina and chromia were present. Alumina alone (as a replacement for chromia) was not as an effective stabilizer as chromia. Although both the alumina-containing catalyst (without chromia) and the reference with chromia had similar initial surface areas (~160 m2/g), the alumina-containing catalyst retained only 74% as much surface area after reaction. Results from the catalysts with 50 wt% alumina suggest that the loss of catalytic activity is due also to the formation of aluminates.