The constantly increasing growth in the number of cars is one of the reasons for the deterioration of the ecological situation in cities and large settlements. In Kazakhstan, on a national scale, the share of motor vehicles in total emissions of pollutants into the atmosphere by all technogenic sources reaches on average 40%, in the mass of industrial waste - 2%. The content of toxic substances in the exhaust of diesel and gasoline engines varies and depends on the type of engine and mode of operation, as well as on the quality of the fuel, the composition of the combustible mixture in the engine cylinders, speed and driving conditions, ignition system and fuel control. The number of all toxic components in the exhaust gas exceeds the maximum permissible standards by tens and hundreds of times. One of the most reliable ways to reduce the toxicity of vehicle exhaust gases and remove harmful substances is the complete oxidation of exhaust components using catalytic compositions on metal or ceramic block carriers. The article accumulates data from the scientific literature about toxicity of different components of exhaust gases and catalytic neutralization of vehicle exhaust gases by various scientific schools.

The article describes some variants of mechanisms of nitro compounds reduction, offered by authors in the scientific literature. The focus is on the description of the work of Kazakh and Russian chemists working in the field of catalysis. In most of the works, the classical scheme of the mechanism of the hydrogenation of Haber-Lukashevich nitrobenzene is confirmed and detailed by experimental methods. One of the interesting aspect of the article is description the mechanism of Ya.A. Dorfman which used the orbital theory of catalysis. The orbital approach of the Ya.A. Dorfman mechanism is constructed in the light of modern orbital representations and is valid for the hydrogenation of the nitro group on various catalysts. Among the discussed mechanisms are ideas of Haber, Debus, Jungers, V.P. Shmonina, Lukashevich, M. Geirovsky, Yu. B. Vasilyev, M.V. Klyuev, E.F. Weinstein, E. Gelder, Ya.A. Dorfman and others.