Design of SiO₂−Al₂O₃−MoO₃ Metathesis Catalysts by Nonhydrolytic Sol−Gel

MoO 3 -based heterogeneous catalysts prepared by dispersion of Mo-oxide species on preformed supports are highly regarded candidates for industrial light olefin metathesis. An original approach for the elaboration of Mo-based catalysts is presented here. Mesoporous ternary Si/Al/Mo mixed oxides are prepared in one step by a nonhydrolytic sol−gel route in nonaqueous medium. Taking advantage of the migration of Mo species during the calcination, effective catalysts with very good textures and highly dispersed surface Mo species are obtained, as shown by XRD, XPS, and TOF-SIMS characterization. The presence of isolated Mo species is evidenced and these species are proposed to be the precursors to the active species in the metathesis of propene. These new materials compare well with catalysts prepared by classical wet impregnation of silica−alumina supports with ammonium heptamolybdate, eventually outperforming them at high Mo loading.