The role of water in selective heterogeneous catalytic oxidation of hydrocarbons

The review discuss the role of water in the selective oxidation of hydrocarbons of different composition and different chemical nature. The review examines the interaction of water with catalysts, mainly based on vanadium and molybdenum oxides, including volume and surface reconstruction, the mechanism of formation of adsorbed forms of water and their impact on the reaction stages. Positive effect of water is manifested in an increase of the activity and selectivity of the catalysts. The acceleration of the catalytic reaction is associated with the generation of new active centers, namely, Bronsted active sites (BAS), as the part of hydroxyl groups product of water dissociation on the catalyst. BAS serve as centers for the primary activation of hydrocarbons, facilitating the subsequent limiting stage of dissociation by Lewis active sites (LAS). Possible ways to increase the selectivity are: acceleration of the main reaction associated with the appearance of BAS, without affecting adverse reactions; inhibition reoxidation of the target product by water competing or displacement of a surface oxygenate precursor; facilitation of the desorption of the target product with the catalyst surface oxidized by water; suppressing the formation of strongly bonded intermediates, regulating the acidity of BAS. All these paths simultaneously reduces the coking the catalysts.