A kinetic study of vapor-phase cyclohexene epoxidation by H2O2 over mesoporous TS-1

Abstract

A kinetic analysis of gas-phase cyclohexene epoxidation by H 2 O 2 over mesoporous TS-1 was performed. The production of cyclohexene oxide was very stable with high selectivity. Based on the kinetics analysis, the gas phase mechanism is proposed to be similar to that of the liquid phase reaction: an Eley-Rideal type mechanism, in which the reaction between a Ti-OOH intermediate and the physisorbed alkene is the rate-determining step. When the partial pressure of water or H 2 O 2 was varied, a compensation effect was observed. Based on the kinetics model, the compensation effect is attributed to variations in the surface coverage of intermediates, specifically the competitive adsorption of water and H 2 O 2 at the Ti active sites. A meaningful activation energy can only be obtained at high surface coverages of H 2 O 2 and was determined to be 40 ± 2 kJ/mol.

Inter-connected and open pore hierarchical TS-1 with controlled framework titanium for catalytic cyclohexene epoxidation

“…Although sodium hydroxide can create mesopores in MFI zeolites it also decreases their relative crystallinity, and in addition increases the amount of extra-framework titanium in the TS-1 [20][21][22] . Recently, organic templates such as tetrapropyl ammonium hydroxide (TPAOH) [23][24][25][26] and a mixture of TPAOH and NaOH 27 have been used to treat TS-1 after synthesis to obtain hollow TS-1. The TPAOH acts as an alkaline and dissolves the zeolite crystals to create mesopores in the TS-1 crystals.…”

Incorporation of Ti as a Pyramidal Framework Site in the Mono‐Layered MCM‐56 Zeolite and its Oxidation Activity

“…In this mechanism titanium atoms activate coordinated H 2 O 2 by withdrawing electrons from the O−O bond making it more susceptible to nucleophilic attack by a substrate, which leads to its oxidation. The mechanism is believed to be of the Rideal‐Eley type and is not dependent on substrate adsorption on the catalyst …”

Kinetic Model of Two‐Phase Epoxidation with Ionic Liquids as Micellar Catalysts

“…However, measurements could not be extended to higher temperatures because H 2 O 2 decomposition becomes a significant side reaction above 80 °C. The activation energy was determined to 49 kJ mol −1 , which is well in the range of intrinsic activation energies (34–50 kJ mol −1 ) reported in the literature for different catalysts in gas or liquid phase epoxidation reactions .…”