(683b) Tuning the Surface Active Sites By Surface Modification of Supported ReOx/(SiO2-Al2O3) Catalysts for Olefin Metathesis
AIChE Annual Meeting
2021 Annual Meeting
Catalysis and Reaction Engineering Division
Fundamentals of Catalysis and Surface Science: Virtual
Monday, November 15, 2021 - 3:48pm to 4:06pm
Due to the global shortage of propylene, the chemical industry is turning to metathesis of ethylene and 2-butene to produce on purpose propylene. Heterogeneous supported ReOx/Al2O3, MoOx/Al2O3 and WOx/SiO2 catalysts have been found to be most efficient for metathesis of olefins. Although the supported ReOx/Al2O3 catalyst has received much attention for olefin metathesis, the effect of the oxide support on olefin metathesis by supported ReOx catalysts is still not well understood. For the most common Al2O3 support, not all rhenia anchoring sites lead to activation of rhenia for olefin metathesis. Modified Al2O3-SiO2 mixed oxide supports are highly effective supports for promoting surface ReOx sites for olefin metathesis. The improved metathesis performance of the Al2O3-SiO2 mixed oxide supports has been attributed to the modified surface Lewis and Brønsted acidity, but supporting data were not provided in these studies. The nature of the surface AlOx, SiOx and ReOx sites present in these mixed oxide supports are still unknown. The objective of the present study is to determine the origin of enhanced performance of the surface ReOx sites on Al2O3-SiO2 mixed oxide supports.
Modern in situ molecular spectroscopy (UV-Vis, Raman, IR and XAS) and chemical probe studies (ammonia chemisorption, C2H4/C4H8-titration, C3H6-TPSR and steady-state propylene self-metathesis) of the surface ReOx sites on Al2O3 and SiO2, and surface modified mixed oxide supports (SiO2/Al2O3, Al2O3/SiO2, and ZSM-5 (Si/Al=15)) were applied to address the origin of the promotional effect. The characterization studies of the supported rhenia catalysts demonstrated that the enhanced activity on Al2O3-SiO2 mixed oxide supports is due to anchoring rhenia at Brønsted acidic Al-(OH)+-Si surface hydroxyls that results in a greater number of activated surface ReOx sites.