The synthesis of highly dispersed noble and base metals over microporous and mesoporous silica

Silica supported noble and base metal heterogeneous catalysts are widely used in a large quantity of commercially important processes. Highly dispersed silica supported metal catalysts can be prepared by strong electrostatic adsorption (SEA), with which metal ammines are strongly adsorbed onto microporous (amorphous) or mesoporous silica at high pH. The PZC (point of zero charge) of amorphous or mesoporous silica was measured by pH shift control experiment. The surface density of adsorbed metal ammines over silica was surveyed as a function of pH to determine the optimal pi I of strongest electrostatic adsorption. The revised physical adsorption (RPA) model can be applied to simulate this process reasonably.;The amorphous silica supported metal catalysts (Pd, Cu, Co, Ru and Ni catalysts) were prepared via SEA and dry impregnation (DI) at different metal loadings, and the prepared catalysts were characterized by a series of techniques such as Temperature Program Reduction (TPR), X-ray Photoelectron Spectroscopy (XPS), Scanning Transmission Electron Microscopy (STEM), Energy Dispersive X-ray Spectroscopy (EDXS). The results show the strong interaction between the adsorbed species and support can affect many facts such as the reduction temperature, the homogeneous distribution of metals over support, and the metal particle sizes of reduced catalysts.;SEA method was also applied to synthesize nano-metal particles (Pt, Pd and Co) on mesoporous silica SBA-15. The adsorption kinetics survey of metal ammines on SBA-15 demonstrates that almost 100% uptake can finish within 5-10 minutes, and strong electrostatic interaction forms in such a short time to generate highly dispersed metals. Lower reduction temperature is beneficial to synthesize small reduced metal particles inside the parallel channels of SBA-15, and narrow the particle size distribution.;Ultimately, the assumption that there is a general correlation between strong interaction in SEA conditions during impregnation and high dispersion of the reduced metal has been verified. Highly dispersed metals can be achieved on microporous and mesoporous silica via SEA, which has potential application for catalyst synthesis in commercial industries.