Metathesis of ethylene with 2-butenes over WOx-, MoOx- and ReOx-based catalysts: understanding the fundamentals of catalyst functioning

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The metathesis of ethylene with 2-butenes to propene is a large-scale process, in which WOx- (and rarely MoOx- and ReOx-) based catalysts together with a co-catalyst (MgO) are applied. Despite the fact that such reaction is thoroughly investigated by academia and industry, there is still a lot of fundamental questions concerning catalyst functioning. Their answering will provide a basis for catalyst design and for identification of reaction conditions required for optimal propene formation. To close such gap, the current project is intended i) to provide fundamentals for the development of active and stable catalysts for the metathesis of ethylene with 2-butenes; ii) to identify optimal conditions of catalyst operation; and iii) to establish structure-reactivity relationships. In order to achieve the project goals, a series of WOx-, MoOx- and ReOx-based catalysts with a well-defined MOx (M = W, Mo or Re) structure will be synthesized and thoroughly characterized by complementary techniques. The catalysts will be tested in metathesis of ethylene with trans-2-butene under steady-state and transient conditions. The influence of different factors (e.g. dispersion of MOx species, the kind of support material, the presence of reducing agent in metathesis feed or metathesis-inactive co-catalysts with these both being used as promoters, catalyst pre-treatment) on the amount of in situ formed active species, which are metal-carbenes, is to be elucidated. Operando tests (IR, Raman, UV-vis) will be performed in order to monitor the changes in catalyst composition and structure during pre-treatment and metathesis reaction. The obtained fundamental insights will be applied for a rational design of improved catalysts as well as general guidelines for efficient catalyst operation including the presence of gas-phase and solid promoters.