MoO3-based heterogeneous catalysts for the metathesis of propene

Abstract

The heterogeneous metathesis of light olefins is a crucial reaction for the regulation of olefins stocks at low energy cost. Molybdenum oxide dispersed at the surface of an inorganic support is a regarded cheap and robust heterogeneous metathesis catalyst. This thesis presents fundamental and applied approaches to the understanding of the active species and to the development of new efficient catalytic materials. A systematic investigation of MoO3/SiO2-(Al2O3) catalysts with variable support composition describes the crucial role of Al. Then, the best support composition is selected and a classical wet impregnation preparation method is inspected in details. For these catalysts, the genesis of active and inactive species during the preparation is described in link with the (limited) performances reached. Alternative MoO3 deposition modes are then explored. Firstly, the wet impregnation with alternative Mo precursors (use of oxalic acid additive or use of molybdenum oxide hydrates solutions) allows impeding the formation of inactive Mo species upon calcination and produces more active catalysts. Secondly, the direct thermal spreading of MoO3 onto the support is identified as an alternative straightforward route to obtain active metathesis catalysts. An innovative non-hydrolytic sol-gel method is then implemented to prepare MoO3-SiO2-Al2O3 mixed oxides. Upon optimization of homogeneity, texture and composition, these samples turn out to be very active metathesis catalysts because highly dispersed molybdate species are stabilized at their surface.