Mesoporous hard-templated Me–Co [Me = Cu, Fe] spinel oxides for water gas shift reaction

Abstract

Copper–cobalt and iron–cobalt oxides, as well as a cobalt oxide sample, were synthesized through the hard template (HT) route by using SBA-15 silica as the HT. Copper- and iron-containing materials with a Me/(Co + Me) atomic ratio of 9 and 17 mol% were obtained and characterized as to their structure, morphology, texture and redox properties by X-ray diffraction, FTIR spectroscopy, transmission electron microscopy, N₂-physisorption and H₂-temperature programmed reduction, respectively. All the oxides were tested in a fixed-bed reactor for the water gas shift reaction in the 200–350 °C temperature range. All the catalysts showed a spinel structure, with the copper ions occupying exclusively the tetrahedral positions in the Cu–Co spinels and the iron ions being present in both tetrahedral and octahedral positions in the Fe–Co spinels. Segregation (to a minor extent) of maghemite phase was detected only for the high-concentration iron–cobalt oxide. The materials were replicas of the topological structure of the template, the channels being void replicas of the former walls of the SBA-15 host and the oxide appearing as nanorods, arranged in a highly ordered way in the case of Cu–Co oxides. Compared to Co₃O₄, the copper-containing and the iron-containing spinels were easier and harder to reduce, respectively. While the catalytic activity of cobalt and iron–cobalt spinels was rather poor, a remarkable water gas shift activity, accompanied (to a minor extent) by methanation, was observed over Cu–Co spinels. The influence of the reduction features on the catalytic performance is discussed.