Combustion of chlorinated volatile organic compounds (VOCs) using bimetallic chromium-copper supported on modified H-ZSM-5 catalyst

Abstract

The paper reports on the performance of chromium or/and copper supported on H-ZSM-5 (Si/Al = 240) modified with silicon tetrachloride (Cr 1.5/SiCl 4-Z, Cu 1.5/SiCl 4-Z and Cr 1.0Cu 0.5/SiCl 4-Z) as catalysts in the combustion of chlorinated VOCs (Cl-VOCs). A reactor operated at a gas hourly space velocity (GHSV) of 32,000 h −1, a temperature between 100 and 500 °C with 2500 ppm of dichloromethane (DCM), trichloromethane (TCM) and trichloroethylene (TCE) is used for activity studies. The deactivation study is conducted at a GHSV of 3800 h −1, at 400 °C for up to 12 h with a feed concentration of 35,000 ppm. Treatment with silicon tetrachloride improves the chemical resistance of H-ZSM-5 against hydrogen chloride. TCM is more reactive compared to DCM but it produces more by-products due to its high chlorine content. The stabilization of TCE is attributed to resonance effects. Water vapor increases the carbon dioxide yield through its role as hydrolysis agent forming reactive carbocations and acting as hydrogen-supplying agent to suppress chlorine-transfer reactions. The deactivation of Cr 1.0Cu 0.5/SiCl 4-Z is mainly due to the chlorination of its metal species, especially with higher Cl/H feed. Coking is limited, particularly with DCM and TCM. In accordance with the Mars–van Krevelen model, the weakening of overall metal reducibility due to chlorination leads to a loss of catalytic activity.