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

Results of the systematic study of the synthesis of highly dispersed framew ork zirconium phosphates stabilized by ammonium, lanthanum, aluminum, manga nese, and cobalt cations are summarized, The synthesis involves the mechano chemical activation of a mixture of solid reactants (salts) or the sol-gel process each followed by the hydrothermal treatment (HTT) of obtained precu rsors in the presence of surfactants, The genesis of dispersed systems unde r 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 nu clei 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 m echanism or the mechanism of oriented mating of primary particles. The crys tallization mechanism in HTT and the reaction system composition influence the nature of resulting complex zirconium phosphate phases, their thermal s tability, dispersity, and porous structure parameters. The relationship bet ween the bulk structure parameters of framework zirconium phosphates, which are controlled by varying the chemical composition and conditions of synth esis, and the surface characteristics of the systems (the strength and conc entration of different Lewis and Bronsted sites) is studied. It is shown th at 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 oxida tive dehydrogenation of propane into propylene.