Impact of heterogeneities in silica-supported copper catalysts on their stability for methanol synthesis

Precipitation and impregnation are two common methods to synthesize heterogeneous catalysts. In this paper we compare the stability and activity of silica-supported catalysts prepared by precipitation or by impregnation, having comparable support morphology and copper weight loading. To obtain catalysts with comparable support morphology, plate-like silica was prepared from the precipitated catalyst. This porous, high surface area plate-like silica was subsequently impregnated with an aqueous copper solution and reduced in hydrogen. Catalysts characterization revealed that catalysts prepared by impregnation contained heterogeneities, present as particles significantly larger than the vast majority, whereas catalysts prepared by precipitation displayed a narrow particle size distribution. In particular the catalyst prepared by impregnation with a copper weight loading of 34 wt% displayed heterogeneities in the form of large particles, which were detrimental for both activity and stability in methanol synthesis from synthesis gas.