(345e) Structural Water Gas Shift Catalysts

Water gas shift (WGS) catalysis is an established industrial technology, but catalyst stability can be improved. Also, the WGS reaction is exothermic and thermodynamically limited at high temperatures. Therefore, a process with more stable catalysts combined with membranes to remove the product hydrogen (H2) is desirable. This research project is developing a process to produce H2 from coal-derived synthesis gas, focusing on improved WGS catalysts with higher thermal stability for incorporation in a monolithic ceramic. The catalyst/ceramic combination will provide structural support for a membrane to remove H2 from the product stream to shift equilibrium toward the products and increase carbon monoxide conversion and H2 production. The overall goal is to produce an integrated catalyst/membrane device with reduced capital costs for H2 production by combining the H2 generation and purification processes. A series of catalysts with iron, chromia, and copper oxides were prepared with varying amounts of alumina and ceria. The catalysts with added alumina and ceria generally produced higher CO conversion rates and were more stable than traditional high temperature WGS catalysts containing only Fe/Cu/Cr oxides. Alumina alone was not an effective replacement for Cr, as the CO rate decreased by 25% compared to the commercial formulation. However, alumina addition increased the surface area and the CO rate of the fresh and unreduced Fe/Cr/Cu catalysts. The catalysts with 10 and 15 wt% alumina produced the highest CO rates per gram of catalyst and had the best thermal stabilities, despite containing less of the Fe3O4 active phase. Alumina additions above 15 wt% were detrimental, as the CO reaction rates of catalysts with 20 wt% or more alumina were less than half that of the base catalyst.. Addition of a small amount (3.9 wt%) of ceria showed even more dramatic effects on CO rate. Although the catalyst containing ceria had lower surface area after use (17.3 m2/g) compared to any of the catalysts containing alumina, the CO conversion rate was comparable to the best catalysts containing alumina. A series of catalysts with varying amounts of CeO2 are being synthesized and tested under WGS reaction conditions. The catalyst with 15 wt% Al2O3 was impregnated into the porous mullitic ceramic disk and evaluated under similar WGS reaction conditions in a larger flow reactor fitted with vanadium H2 transport membranes. The supported catalyst was slightly more stable than the palletized catalysts described above, possibly because of a synergistic interaction with the alumina in the ceramic. This type of ceramic was selected because it requires lower firing temperatures and has high chemical, mechanical, and thermal stability