Nanoheterogeneous catalysis: Definition, state, and research prospects (Review)

This review is concerned with the analysis of nanoheterogeneous catalysis (catalysis in heterogeneous-dispersed systems with nanosized particles of the dispersed phase) in the hydroconversion of a vacuum distillation residue, hydrogenation of individual aromatic hydrocarbons and technical mixtures, and Fischer–Tropsch synthesis. For nanoheterogeneous catalysis, in addition to factors that are typical for heterogeneous catalysis, important factors are the size effect, the all-round accessibility of catalytically active species to reagents, the absence of a porous structure, a high efficiency of heat transfer in the dispersion medium, and an extremely low mass concentration of the catalyst in the suspension reactor (0.05–0.5%) at a high concentration of nanoparticles per reactor volume unit (1013–1015 particles per cubic centimeter). A fine tuning of catalytic processes may be performed in nanoheterogeneous catalysis via a change in the morphology, size, and structure of nanoparticles and variation in their concentration in a suspension reactor. In many cases, the aggregation of nanoparticles accompanied by the formation of nanoaggregates may become the decisive factor for the final outcome of the test reaction and special efforts are needed to stabilize the suspension of catalytically active particles. Technologies based on catalysis by nanosized particles of the dispersed phase have undergone benchmark and pilot tests and are entering the period of wide implementation in the hydroconversion of oil vacuum distillation residue and partially in the Fischer–Tropsch synthesis.