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

The catalytic combustion of chlorobenzene on a 2 wt.% Pt/gamma-Al2O3 cataly st in binary mixtures with various hydrocarbons (toluene, benzene, cyclohex ane, cyclohexene, 1,4-cyclohexadiene, 2-butene, and ethene) and with carbon monoxide has been explored. For all binary mixtures used the (excess of) a dded hydrocarbon increased the rate of conversion of chlorobenzene. With 2- butene, T-50% and T-100% for chlorobenzene were reduced by 100 and 200 degr ees C, respectively. Toluene and ethene were almost equally efficient as 2- butene. Co-feeding benzene or carbon monoxide resulted in a much smaller de crease of the T-50%. The additional heat and water production in hydrocarbo n combustion may contribute to some extent to the observed rate acceleratio n, 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 polychlorin ated benzenes, which are formed as byproducts in the combustion of chlorobe nzene on Pt/gamma-Al2O3. Again, especially toluene, ethene, and 2-butene we re very efficient. Benzene - as well as cyclohexane, cyclohexene, and 1,4-c yclohexadiene, which were converted in situ into benzene - was much less ef fective, due to chlorination of the aromatic nucleus. In chlorobenzene-CO m ixtures 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 format ion of byproducts. (C) 2000 Elsevier Science B.V. All rights reserved.