THE REDUCTION BEHAVIOR OF SILICA-SUPPORTED COPPER-CATALYSTS PREPARED BY DEPOSITION PRECIPITATION

The reduction behaviour of silica-supported copper catalysts prepared by homogeneous deposition-precipitation has been studied by temperature-programmed reduction (TPR), differential thermogravimetry (DTG), in-situ diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy, and evolved gas analysis (EGA). Preparation by homogeneous deposition-precipitation produces catalyst precursors in which the copper ions are highly dispersed over the silica support, and which show reduction behaviour similar to that of the mineral copper hydrosilicate, chrysocolla. Calcination of the catalyst precursors at 700 K leads to decomposition of the copper hydrosilicate, causing subsequent reduction to occur at a lower temperature. During initial reduction of the chrysocolla-like precursors, the consumption of hydrogen and the release of water are not synchronous. Water formed by the reduction is retained in the catalyst, probably due to participation of water in a reorganization of the silica support. During the second reduction stage of silica-supported copper oxide particles, formed by previous reduction and re-oxidation of the chrysocolla-like precursor, the consumption of hydrogen and the release of water do occur simultaneously. Finally, the influence of the composition of the reducing gas atmosphere on the reduction behaviour of the catalysts has been investigated. Increasing the hydrogen concentration in the reducing gas mixture from 5 to 50 vol.% does not affect the on-set of the reduction reaction, whereas addition of about 2.4 vol.% H2O to the reducing gas mixture leads to significantly higher on-set temperatures. Once initiated, the reduction proceeds more rapidly at higher hydrogen partial pressures. © 1990.