Catalytic Combustion of Vinyl Chloride Emission over a TiO 2 –MnO x Catalyst

Abstract

TiO₂–MnO _x catalyst samples with different Ti/(Ti + Mn) molar ratios (2:3, 3:4, 4:5, 5:6, 6:7 and 1) prepared by the citric acid (CA) sol-gel method were studied in the catalytic combustion of vinyl chloride (VC) emission. The effects of preparation conditions and operation parameters on the catalytic performance of TiO₂–MnO _x were investigated. The catalyst samples were characterised by N₂ adsorption, X-ray diffraction (XRD) and H₂-temperature programmed reduction (H₂-TPR). In the catalytic combustion of VC over TiO₂–MnO _x , products containing HCl, CO₂, and H₂O were obtained and there were no by-products such as chlorohydrocarbons and chlorine. The TiO₂–MnO _x catalyst with the molar ratio of CA/Mn/Ti = 0.30:0.20:0.80 showed the best catalytic performance and had better operating flexibility over the ranges of gas hourly space velocity (GHSV) of 15000–100000 h⁻¹ and VC concentration of 0.05–2.00%. The temperatures at 50% conversion (140 °C) and at 99% conversion (220 °C) were achieved at a VC concentration of 0.1% and GHSV of 15000 h⁻¹. XRD characterisation indicated that only the characteristic diffraction peaks of TiO₂ with the anatase structure appeared and no characteristic diffraction peaks of MnO _x species appeared for the TiO₂–MnO _x catalyst. XRD and H₂-TPR results indicated that Mn ions were incorporated into the TiO₂ lattice to form a Ti–Mn–O solid solution, which enhanced the reactivity of active oxygen species on the catalyst surface and thereby promoted the catalyst activity.