(609c) Highly Dispersed Noble And Base Metals On Amorphous And Mesoporous Silica Via Strong Electrostatic Adsorption
Silica supported metal heterogeneous catalysts are widely used in a large quantity of commercially important processes for chemical and pharmaceutical production, environmental protection and pollution control, energy production, and etc . Among all the catalyst preparation methods, impregnation method is the simplest, least expensive, and most prevalent . Highly dispersed silica supported metal catalyst can be prepared by strong electrostatic adsorption (SEA), with which metal ammines are selectively adsorbed onto 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 pH of strongest electrostatic adsorption. The revised physical adsorption (RPA) model can be applied to simulate this process reasonably. Meanwhile, the silica supported metal catalysts were prepared via SEA impregnation method and Dry impregnation (DI) method at different metal loadings, and the prepared catalysts were characterized by a series of characterization techniques such as Temperature Program Reduction (TPR), X-ray Photoelectron Spectroscopy (XPS), Scanning Transmission Electron Microscopy (STEM), Energy Dispersive X-ray Spectroscopy (EDXS), and so on. The results show the strong interaction between the adsorbed species and support can affect many facts such as the reduction temperature, the even distribution of metals over support, and the metal particle sizes of reduced catalysts. There appears to be a correlation between strong electrostatic adsorption of metal precursor and high dispersion of the reduced metal.
References:  John R. Regalbuto, Surface and Nanomolecular Catalysis, Taylor and Francis/CRC Press, 2006, 126  Marc Schreier and John R. Regalbuto, Journal of Catalysis 225(2004), 190