(641f) In Situ and Operando Raman/IR/UV-Vis/MS Spectroscopic Studies of Propylene Metathesis by Supported Wox/SiO2 Catalysts

SiO₂-supported tungsten oxide catalysts are used for high temperature (300-400 °C) metathesis of low molecular olefins such as production of ethylene and butene from propylene as well as the reverse reaction for production of propylene. Surprisingly, almost no characterization studies have been reported about olefin metathesis heterogeneous catalysts under reaction conditions. The objective of this investigation is to obtain fundamental insights about the catalytic active sites and surface reaction intermediates present during propylene metathesis over supported WO₃/SiO₂ catalysts.

The SiO₂-supported catalysts were synthesized by conventional incipient-wetness impregnation of ammonium metatungstate (AMT), solvothermal reaction between AMT and oleylamine (NP) and controlling decomposition/reduction of AMT using trimethylamine N-oxide (sNP). The catalysts were characterized with operando Raman and UV-vis spectroscopy during propylene metathesis.

 The new insights generated with the operando spectroscopy experiments reveal for the first time the molecular structure-activity relationships of SiO₂-supported tungsten oxide heterogeneous catalysts for propylene metathesis.  The dispersed surface WO_x species are the selective catalytic active sites for propylene metathesis and the crystalline WO₃ NPs are unselective for propylene metathesis.