Well-defined silica-supported catalysts, catalyze alkene metathesis,and the cationic species display unprecedented activity for abroad range of substrates, especially for terminal olefins with turnover numbers above 1.2 million (for propene).
link to blog: Buchmeiser,Copéret et al.. Cationic Silica‐Supported N‐Heterocyclic Carbene Tungsten Oxo Alkylidene Sites: Highly Active and Stable Catalysts for Olefin Metathesis. Angewandte Chemie International Edition. 2016 Feb 1.