Density functional theory study of the ethylene epoxidation over Ti-substituted silicalite (TS-1)

Abstract

The mechanism of ethylene epoxidation with hydrogen peroxide over Ti-substituted silicalite (TS-1) catalyst was investigated by using both the cluster and embedded cluster approaches at the B3LYP/6-31G(d) level of theory. The complete catalytic cycle was determined. The epoxidation of ethylene consists of three steps. First, the chemisorption of H 2 O 2 at the Ti active site forms the oxygen donating Ti-OOH species and then the transfer of an oxygen atom from the Ti-OOH species to the adsorbed ethylene. The final step is the dehydration of the Ti-OH species to regenerate to active center. The oxygen atom transfer step was found to be the rate-limiting step with the zero-point energy corrected barrier of 17.0 kcal/mol using the embedded cluster model at B3LYP/6-31G(d) level of theory, which is in agreement with the experimental estimate of about 16.7 kcal/mol. Regeneration of the active center by dehydration of the Ti-OOH species was found to have a rather small barrier and the overall process is exothermic. Our results also show that inclusion of the effects of the zeolite crystal framework is crucial for obtaining quantitative energetic information. For instance, the Madelung potential increases the barrier of the oxygen atom transfer step by 5.0 kcal/mol.

Heterogeneous Catalysis of Alkene Epoxidation

“…DFT calculations that include solvent molecules and larger SiO x clusters around the Ti center also indicate hydrogen bonding -both of the hydroperoxide hydrogen to neighboring framework oxygens [115] and from water and neighboring silanol species to the central O atom of the OOH group [103]. DFT calculations that include solvent molecules and larger SiO x clusters around the Ti center also indicate hydrogen bonding -both of the hydroperoxide hydrogen to neighboring framework oxygens [115] and from water and neighboring silanol species to the central O atom of the OOH group [103].…”

Strengths, Weaknesses, Opportunities and Threats: Computational Studies of Mn- and Fe-Catalyzed Epoxidations

“…In the case of vanadium, this was first systematically studied by Vandichel et al [104], whereas the case of titanium was tackled earlier by Sever and Root [111]. Some theoretical studies on titanium-catalyzed epoxidations also focused on this metal's ability to efficiently catalyze the epoxidation of olefins when immobilized into a heterogeneous matrix, such as silicates [112] or polyoxometalates [113,114]. These theoretical studies follow the same trend observed in the case of manganese-and iron-catalyzed epoxidations, with a predominance of DFT, with B3LYP as the preferred density function.…”

Heteroatomic Zn‐MWW Zeolite Developed for Catalytic Dehydrogenation Reactions: A Combined Experimental and DFT Study

“…Fe-ZSM-5 shows superiorp erformance in selectivec atalytic reduction (SCR) with ammonia, [6] and is significantly better than Fe-doped ZSM-5 and bare ZSM-5. [7] Ti-Y zeolite, [8] Ti-b zeolite, [9] and TS-1 [10] are effectivee poxidation catalysts. B-ZSM-5 has wide applications in isomerization [11] and dehydration.…”