New Approaches to the Preparation of Highly Efficient Chromium-Containing Oxide Catalysts for the Water Gas Shift Reaction

It was found experimentally that the solutions of Cr(3+) nitrate and the nitrates of other metals that are the constituents of Cr-containing catalysts can be prepared by dissolving a corresponding metal (for example, cast iron and electrolytic copper) in a solution of chromic anhydride and nitric acid to reach the quantitative reduction of Cr(6+) without the formation of nitrogen oxides. Analogously, the oxidation of Fe(2+) cations to Fe(3+) coupled with the reduction of hexavalent chromium can be performed. The precipitation of Fe(3+), Cr(3+), and Cu(2+) ions at a ratio of Fe : Cr = 9 and a concentration of Cu(2+) to 20 at % can result in the formation of a partially hydrated oxide with the hydrohematite structure-a dispersed and highly defective oxide structure with a high specific surface area more than 300 m(2)/g and a higher thermal stability, as compared with the goethite phase (alpha-FeOOH). The dehydration of hydrohematite occurred at a noticeable rate at temperatures higher than 400 degrees C. Hydrohematite promoted with copper cations exhibited high activity below 400 degrees C; this can decrease the starting temperature of the adiabatic high-temperature WGSR to 300 degrees C or below.