Synthesis and characterization of Sn-Beta as a selective oxidation catalyst

The tin zeolite Beta (Sn-Beta = zeolite Beta structure with framework incorporated tin) is synthesized and used as a heterogeneous catalyst for the Baeyer-Villiger (BV) reaction with hydrogen peroxide. Cyclic ketones are transformed into the corresponding lactones with very high selectivity using hydrogen peroxide as a replacement of the environmentally unfriendly peracetic acid. This new oxidation system can also be used for unsaturated ketones, which are oxidized to the corresponding unsaturated lactones with very high chemoselectivity. In some BV reactions the selectivity obtained is similar to that in the equivalent enzyme reaction. The catalytic Sn sites have been characterized using a combination of characterization techniques including TEM, FTIR, XPS and in-situ EXAFS. The most selective Sn-Beta sample, activated using a wet air calcination, shows high weak Lewis acidity and high framework tin. The data from this detailed characterization study provides a scientific basis for a deeper understanding of this fascinating catalyst system.