Abstract
Silica-supported tungsten catalysts with various tungsten oxide loadings were physically mixed with micro- or nano-sized SiO2 excess supports and investigated in the metathesis of ethylene and trans-2-butene to propylene. Adding nano-sized SiO2 excess support led to higher trans-2-butene conversion and propylene yield than those of micro-one and also removed the induction period. It was indicated from FT-Raman spectra and in situ UV–vis spectra that silica-supported tungsten catalysts mixed with nano-sized SiO2 excess support had the higher ratio of isolated surface tetrahedral tungsten oxide species to WO3 crystal and could be well-dispersed than micro-one. The characterization results of the separated nano-sized SiO2 excess support from the spent catalyst by in situ Raman spectroscopy clearly exhibited the presence of isolated surface tetrahedral tungsten oxide species, the active site precursor of metathesis reaction, on the separated nano-sized SiO2 excess support, confirming the thermal spreading of tungsten from the original catalysts to the nano-sized SiO2 and creating more isolated surface tetrahedral tungsten oxide species.
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