Effects of Crystallinity and Pore Architecture of Titanium Silicalites on α-Pinene Oxidation

Titanium silicalite-1 (TS-1) is an effective catalyst, but its limited pore size restricts the access of bulky substrates such as α-pinene. In our previous studies, a TS-1 catalyst with a Si/Ti molar ratio of 20:1 demonstrated high activity in α-pinene oxidation but suffered from diffusion limitations. To overcome this drawback, four new titanium silicate catalysts were synthesized using the reference TS-1 as the parent material (TS-1 catalyst with the Si/Ti molar ratio of 20:1). MTS-1_1 and MTS-1_2 were prepared via a co-templating method, while HTS-1_1 and HTS-1_2 were obtained through post-synthetic recrystallization using triethylamine (method I) or sulfuric acid followed by triethylamine (method II). All catalysts were characterized by UV–Vis, FTIR, XRD, SEM, EDXRF, and nitrogen sorption, and their activity was tested in solvent-free oxidation of α-pinene using molecular oxygen. The influence of temperature, catalyst content, and reaction time on the conversion of α-pinene and the selectivities of the main products was investigated. All modified materials exhibited higher catalytic activity than the reference TS-1 material. HTS-1_2 showed the best results, achieving the conversion of α-pinene of 21 mol% and the selectivity of transformation to α-pinene oxide of 35 mol%. Verbenol and verbenone were also formed as valuable oxygenated products. The developed catalysts enable a green and efficient transformation of renewable α-pinene into high-value derivatives.