Titanium impregnated borosilicate zeolites for epoxidation catalysis

Titanium containing molecular sieves, known as effective epoxidation catalysts, can be prepared either by direct synthesis or by post-synthesis impregnation. Controlled incorporation of titanium during the post-synthesis modification can be achieved when titanium atoms are inserted into the framework positions previously occupied by heteroatoms such as boron. In this contribution, we report the post-synthesis incorporation of titanium into borosilicates SSZ-24, SSZ-33, SSZ-42 and CIT-5. Parent borosilicates were deboronated using an HCl solution and subsequently impregnated with titanium (IV) butoxide or titanium (IV) chloride. The character of the titanium active sites was investigated using DR-UV/Vis spectroscopy showing that the titanium was incorporated into the framework positions with tetrahedral coordination. In some samples, other titanium species were present as well. The prepared Ti-SSZ-33 provides high yield of cyclooctene oxide 28.3% (after 240 min at 60 degrees C in acetonitrile, substrate/catalyst ratio = 10, H2O2 used as oxidant) in comparison with commonly used TS-1 (2.9%). On the other hand, impregnated zeolites SSZ-24, SSZ-42 and CIT-5 provided lower yields of cyclooctene oxide then the TS-1. The materials were found to catalyse the epoxidation of norbornene and linalool as well. The order of catalysts performance was similar for both substrates: Ti-SSZ-33 (norbornene oxide yield 15.4% after 240 min) > Ti-CIT-5 (yield 3.3%) > TS-1(yield 1.8%) > Ti-SSZ-42 (yield 0.8%); Ti-SSZ-33 (linalool oxide yield 133% after 320 min) > Ti-CIT-5 (yield 3.6%) > TS-1(yield 3.5%) > Ti-SSZ-42 (yield 1.3%)>Ti-SSZ-24 (yield 0.5%). (C) 2015 Elsevier Inc. All rights reserved.