New approaches to the preparation of highly efficient chromium-containing oxide catalysts for the water gas shift reaction

Abstract

It was found experimentally that the solutions of Cr3+ 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 Cr6+ without the formation of nitrogen oxides. Analogously, the oxidation of Fe2+ cations to Fe3+ coupled with the reduction of hexavalent chromium can be performed. The precipitation of Fe3+, Cr3+, and Cu2+ ions at a ratio of Fe: Cr = 9 and a concentration of Cu2+ 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 m2/g and a higher thermal stability, as compared with the goethite phase (α-FeOOH). The dehydration of hydrohematite occurred at a noticeable rate at temperatures higher than 400°C. Hydrohematite promoted with copper cations exhibited high activity below 400°C; this can decrease the starting temperature of the adiabatic high-temperature WGSR to 300°C or below.