Metathesis of C4 olefin over Mo-based heterogeneous catalysts: A novel route to propene and isopentene

A novel route with high yields of propene and isopentene on the basis of consecutive metathesis of 1-butene and isobutene is proposed. Two series of Mo-based catalysts supported on γ-Al2O3 and HMOR-Al2O3 composite materials were prepared and evaluated in a fixed bed reactor. Experimental results revealed that three interesting reactions occurred on the catalysts, i.e. 1-C4= → 2-C4= (Isomerization I), 2-C4= + 1-C4= → C3= + 2-C5= (Metathesis I), 2-C4= + i-C4= → C3= + i-C5= (Metathesis II). Isomerization I was the prerequisite step of the following two metathesis reactions. Metathesis I was more acidity-sensitive and it could happen at low temperatures provided that the catalyst acidity was sufficient. Metathesis II, as the targeted reaction, was proved to be more temperature-sensitive, and high reaction temperatures were preferable for the metathesis of 2-butene and isobutene. 6Mo/Al2O3 exhibited the best catalytic metathesis performance among the candidate catalysts in the consecutive metathesis of 1-butene and isobutene. Furthermore, isopentene selectivity could be highly enhanced through the steam treatment of γ-Al2O3 support. The modifications of alumina support led to the different distribution of Mo species and the formation of more Mo species in octahedral state may contribute to the preferential activation of Metathesis II.

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► Mo/Al2O3 with suitable acidity exhibits the best catalytic performance.
► Metathesis of 2-butene and isobutene is more temperature-sensitive.
► Metathesis of 1-butene and 2-butene is more acid-sensitive.
► States of Mo species are closely related to the metathesis activation of different olefins.