Increased combustion rate of chlorobenzene on Pt/γ-Al2O3 in binary mixtures with hydrocarbons and with carbon monoxide

Abstract

The catalytic combustion of chlorobenzene on a 2wt.% Pt/γ-Al2O3 catalyst in binary mixtures with various hydrocarbons (toluene, benzene, cyclohexane, cyclohexene, 1,4-cyclohexadiene, 2-butene, and ethene) and with carbon monoxide has been explored. For all binary mixtures used the (excess of) added hydrocarbon increased the rate of conversion of chlorobenzene. With 2-butene, T50% and T100% for chlorobenzene were reduced by 100 and 200°C, respectively. Toluene and ethene were almost equally efficient as 2-butene. Co-feeding benzene or carbon monoxide resulted in a much smaller decrease of the T50%. The additional heat and water production in hydrocarbon combustion may contribute to some extent to the observed rate acceleration, but removal of Cl from the surface due to the hydrocarbon appears to be the major factor.The co-feeding of hydrocarbons invariably reduced the output of polychlorinated benzenes, which are formed as byproducts in the combustion of chlorobenzene on Pt/γ-Al2O3. Again, especially toluene, ethene, and 2-butene were very efficient. Benzene — as well as cyclohexane, cyclohexene, and 1,4-cyclohexadiene, which were converted in situ into benzene — was much less effective, due to chlorination of the aromatic nucleus. In chlorobenzene–CO mixtures the levels of polychlorinated benzenes were almost as high as with chlorobenzene per se. Removal of Cl from the surface (mainly in the form of HCl) by (non-aromatic) hydrocarbons is responsible for reducing the formation of byproducts.