Orbital asymmetric hybridization enhances surface Lewis acid-base reactions of charged clay catalysts

Abstract

A strong electric field of 108–10 V/m could be produced from the surface charges of clay. In this study, the asymmetric hybridization of atomic orbitals in the electric field at the clay surface substantially enhances the Lewis acid-base reactions between the surface O and Cu2+/Ca2+/Mg2+/H2O. This has been confirmed by cationic adsorption kinetics, energies, critical coagulation concentrations (CCCs) and infrared spectral analyses of –OH and Si-O stretches for H2O and clay crystal respectively. The enhanced Lewis acid-base reaction energy for Cu2+, Ca2+ and Mg2+ at charged clay surface is found in an order of Cu2+(−27.21 kJ/mol) > Ca2+(−15.51 kJ/mol) > Mg2+(−6.061 kJ/mol). For surface H2O, a new blueshift adsorption peak (3612 cm−1) is observed in the infrared spectral analyses which indicate a strong Lewis acid-base reaction for H2O at charged clay surface. This study indicates that, for the catalytic activities of charged clay catalysts, the background cation types and concentrations, the electric field intensity and the orbital asymmetric hybridization effect at charged clay surface would be coupled and intertwined. Importantly, in those factors/effects the electric field and its initiated orbital asymmetric hybridization of surface atoms/cations should play the critical roles, and thus these two key factors should be emphasized in clay catalyst design.