The oxidative dehydrogenation (OD) of ethylbenzene (EB) has been investigated over different catalysts of xCaO/SiO2 and yP/XCaO/SiO2 composition. It has been shown that the texture characteristics of initial SiO2 exert an important influence on the activity of catalysts obtained on their basis. Higher conversion of ethylbenzene and selectivity on styrene are observed in the case of macroporous silica gels. The yield of styrene and quantity of carbon deposits (CD) in the initial reaction period are increased symbately. In the stationary reaction period achievable in 1-6 h after beginning of reaction, depending on texture characteristics of catalysts, maximal conversion of EB and minimal rate of accumulation of carbon deposits are observed over catalyst surface. In this period of process catalytically active system represents carbon deposits formed over catalyst surface and inclusive various carbonyl-containing groups. Catalysts are not passive carriers on which carbon deposits are formed; on the contrary, structure and catalytic activity of carbon deposits strongly depend on composition, texture characteristics and acid-base properties of used catalysts. (c) 2005 Elsevier B.V. All rights reserved.