Single Site Catalysts for Propene Dehydrogenation

Selective dehydrogenation of light alkanes to olefins is a key technology for converting abundant alkane feedstocks into high value precursors for the polymer and fuel industries. A number of single site, silica-supported cations are able to catalyze this reaction with high selectivity; however, the design principles governing catalytic activity are not yet known. X-ray absorption spectroscopy indicates that reactivity proceeds without a change of oxidation state at the active site, and in some cases, metal hydride intermediates may be identified by Raman spectroscopy. These results are consistent with density functional modeling suggesting a heterolytic C-H bond cleavage mechanism for alkane dehydrogenation. Activity of the site is found to depend on both the Lewis acidity of the cation and the metal-oxygen bond strength between the cation and the silica support. Greater understanding of these structure-function relationships has guided synthesis of precatalysts that more readily form the active metal hydride structure under reaction conditions, leading to significant increases in catalytic performance.