Metal‐Support interaction in Silica‐Supported Cobalt Catalyst

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AbstractThe variations in catalytic properties for CO hydrogenation and adsorptive properties for H2 and CO of silica‐supported cobalt catalyst as a function of reduction temperature (400 to 700 °C) were investigated. A mild sintering of cobalt metal from 130 Å to 145 Å occurred only when the reduction temperature was further increased from 600 to 700 °C. However, a monotone decrease in the activity (per gram Co) for CO hydrogenation was observed with increasing reduction temperature. This is accompanied with a decrease in methane and an increase in olefin formation. The decrease in activity can not be accounted for by the variation of crystallite size of cobalt metal. A concurrent suppression in the amount of hydrogen and CO adsorptions was observed after reduction temperature was raised to 700 °C. The turnover frequencies, based on cobalt dispersion estimated from H2 and CO chemisorption, remained, more or less, similar with increasing reduction temperature from 400 to 600 °C, but increased ca. 3 and 1.5 times, respectively, at 700 °C. The relative amount of subcarbonyl species (2062 cm−1) with respect to the linear adsorbed CO (2010 cm−1) was found to increase as well. Furthermore, reduction of silica surface at 700 °C was indicated by the presence of ˜Si‐H, which was detected by infrared spectroscopy at 2294 cm−1. This shows the presence of metal‐support interaction for silica‐supported cobalt systems after reduction treatment at 700 °C.