Changjiu Xia

Heterogeneous oxidation of cyclohexanone catalyzed by TS-1: Combined experimental and DFT studies

Abstract The reaction mechanism of the oxidation of cyclohexanone catalyzed by titanium silicate zeolite TS-1 using aqueous H 2 O 2 as the oxidant was investigated by combining density function theory (DFT) calculations with experimental studies. DFT calculations showed that H 2 O 2 was adsorbed and activated at the tetrahedral Ti sites. By taking into account the adsorption energy, molecular size, steric hindrance and structural information, a reaction mechanism of Baeyer-Villiger oxidation catalyzed by TS-1 that involves the activation of H 2 O 2 was proposed. Experimental studies showed that the major products of cyclohexanone oxidation by H 2 O 2 catalyzed by a hollow TS-1 zeolite were ɛ-carprolactone, 6-hydroxyhexanoic acid, and adipic acid. These products were analyzed by GC-MS and were in good agreement with the proposed mechanism. Our studies showed that the reaction mechanism on TS-1 zeolite was different from that on Sn-beta zeolite.

Chlorohydrination of allyl chloride with HCl and H2O2 catalyzed by hollow titanium silicate zeolite to produce dichloropropanol

Overall, over 95% of epichlorohydrin is industrially manufactured via the chlorohydrination route with hazardous Cl2 as a reagent, which brings serious operation and pollution problems. Herein, we describe a novel Cl2-free process for the synthesis of dichloropropanols from allyl chloride with H2O2 and HCl catalyzed by hollow titanium silicate zeolite under mild conditions. A high conversion and overall dichloropropanol selectivity exceeding 95% are simultaneously achieved, and the heterogeneous catalyst is highly stable and amenable for reuse. Comprehensive experimental and spectroscopic data suggest that the Lewis acidity of the framework Ti species has a synergistic effect with the Bronsted acidity of HCl that promotes the epoxidation of allyl chloride and the ring opening of the epoxy groups.

Hollow Titanium Silicalite Zeolite: From Fundamental Research to Commercial Application in Environmental-Friendly Catalytic Oxidation Processes

The systematical investigation on the synthesis, characterization, formation mecha‐ nism, and catalytic application of hollow titanium silicalite (HTS) zeolite has been reviewed. HTS is prepared through a “dissolution–recrystallization” post-treatment in the presence of template under hydrothermal conditions. Compared with TS-1, HTS is of unique hollow voids and with high framework Ti content, which significantly increase the mass diffusion and the amount of active sites, respectively. Thus, HTS zeolite displays high catalytic activity and stability in many oxidation processes with H2O2 oxidant, that is, cyclohexanone ammoximation, phenol hydroxylation, propy‐ lene epoxidation, Baeyer-Villiger oxidation of cyclohexanone, and selective oxidation of aromatics and cycloalkanes. The former three ones have been commercialized and run smoothly, which have promising economic and environmental significance.