Scientific bases for the synthesis of highly dispersed framework zirconium phosphate catalysts for paraffin isomerization and selective oxidation

Abstract

Results of the systematic study of the synthesis of highly dispersed framework zirconium phosphates stabilized by ammonium, lanthanum, aluminum, manganese, and cobalt cations are summarized. The synthesis involves the mechanochemical activation of a mixture of solid reactants (salts) or the sol–gel process each followed by the hydrothermal treatment (HTT) of obtained precursors in the presence of surfactants. The genesis of dispersed systems under investigation is studied by modern physical methods providing information on the state of the bulk and surface of the systems. It is found that the local structure of sol nanoparticles and zirconium phosphate crystalline nuclei arising from mechanochemical activation products depends on the nature of initial substances. This, in its turn, makes different crystallization mechanisms possible during the HTT process: the dissolution/precipitation mechanism or the mechanism of oriented mating of primary particles. The crystallization mechanism in HTT and the reaction system composition influence the nature of resulting complex zirconium phosphate phases, their thermal stability, dispersity, and porous structure parameters. The relationship between the bulk structure parameters of framework zirconium phosphates, which are controlled by varying the chemical composition and conditions of synthesis, and the surface characteristics of the systems (the strength and concentration of different Lewis and Br@nsted sites) is studied. It is shown that systems based on framework zirconium phosphates are promising catalysts for paraffin (pentane and hexane) isomerization, the selective oxidation of methane by oxygen into synthesis gas at short contact times, and the oxidative dehydrogenation of propane into propylene.