Conditions of Formation of Copper Phyllosilicates in Silica-Supported Copper Catalysts Prepared by Selective Adsorption

Abstract

It is shown that, during the preparation of Cu/SiO2 samples by selective adsorption of copper tetraammine complex [Cu(NH3)4(H2O)2]2+ on silica, two types of supported CuII species form: grafted CuII ions and copper phyllosilicate. The formation of grafted CuII ions results from electrostatic adsorption of CuII ammine complex cations in solution onto the surface of silica particles negatively charged due to the high solution pH. Grafting of CuII ions occurs during the subsequent drying step. The formation of copper phyllosilicate takes place in solution. It results from a reaction between silicic acid arising from silica dissolution and [Cu(OH)2(H2O)4]0 complex in solution. Both CuII species lead to small metal particles after reduction. Several preparation parameters were investigated in this paper: the metal precursor concentration, the pH of the precursor solution, the solution/silica contact time, and the addition of ammonium nitrate to the precursor solution. The amount of copper phyllosilicate depe...