Thermal Activation of a Clayzic Catalyst Useful for Friedel–Crafts Reactions: HCl Evolved with Creation of Active Sites in Different Thermal Treatments to ZnCl₂/Mont-K10

Abstract

Thermal activation of clayzic catalyst has been thoroughly investigated by calcining anhydrous ZnCl₂ impregnated on Mont-K10 with different ZnCl₂ loadings (0.5-2.0 mmol g^-1) under static or flowing air at 270 °C and also under N₂ flow at different temperatures (150-400 °C). Depending upon the ZnCl₂ loading and calcination temperatures, an appreciable amount of HCl is evolved in the thermal activation, indicating an occurrence of reaction between the ZnCl₂ and the surface hydroxyl groups of the clay (- OH + ZnCl₂→ - O - Zn - Cl + HCl), leading to formation of new Lewis acid sites (- O - Zn -Cl). The Cl/Zn ratio, surface area and catalytic activity (in the benzene benzylation by benzyl chloride at 80 °C) of the clayzic formed in the thermal activation are influenced markedly by the ZnCl₂ loading and calcination conditions (temperature and gas atmosphere). The maximum catalytic activity for the clayzic is observed at the optimum ZnCl₂ loading (about 1.0 mmol g^-1) and calcination temperature (about 270 °C). The thermal activation at 270 °C under flowing N₂ led to a most active clayzic catalyst for the benzene benzylation. A temperature-programmed evolution of HCl in the calcination of ZnCl₂/Mont-K10 with different ZnCl₂ loadings from 25 to 400 °C at a linear heating rate of 2 °C min^-1 has also been investigated.