《Table 4 Adsorption energy of cyclohexanone and H2O2 on the Ti-and Al-clusters》

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《Environmentally-Friendly Catalytic Oxidation of Cyclohexanone with 30% H_2O_2 Solution: A Comparison Study between Hollow Titanium Silicate and Dealuminated HBEA Zeolites》

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In order to investigate the different mechanisms of cyclohexanone oxidation catalyzed by two different catalysts，the molecular simulation methods were introduced to calculate the adsorption and activation of reagent molecules and determine their possible reaction pathways and their corresponding geometric structures and energy files.Herein，the trigonal Al（OSiH3）3 and tetrahedral Ti（OSiH3）4 species are chosen as the Lewis acid sites for the DHBEA and HTS zeolites，respectively.It is found that both cyclohexanone and H2O2 molecules can be adsorbed on both Ti and Al clusters，which are attributed to the accepting-donating behavior of lone electron pairs between Lewis acid sites and the O atoms in cyclohexanone and H2O2 molecules，as shown in Figure 4.When cyclohexanone and H2O2 molecules adsorbed on the Lewis acid sites of trigonal Al species，the corresponding adsorption energy is-83.27 kJ/mol and-21.38 kJ/mol，respectively，as illustrated in Table4.It means that cyclohexanone molecules are prone to be adsorbed on the Lewis acid sites of DHBEA zeolite，rather than H2O2 molecules.Meanwhile，the adsorption energy of cyclohexanone and H2O2 molecules on the tetrahedral Ti sites is-135.1 kJ/mol and-384.6 kJ/mol，respectively.It is indicated that H2O2 molecules are much more easily to be adsorbed on the framework Ti species of HTS zeolite.Thus，it infers that the adsorption behavior of DHBEA zeolite is different from that of HTS zeolite.When the cyclohexanone and H2O2 molecules are adsorbed on the trigonal Al species，the charges of the C atom of carbonyl group and the Ob atom of H2O2 are0.50 and-0.39，while those in the original molecules are0.40 and-0.43，respectively，as shown in Table 5.This fact suggests that the carbonyl groups in cyclohexanone molecules become more activated，but there is no impact on the activation of H2O2 molecules after they are adsorbed on the Lewis acid sites of Al species.Furthermore，there are abundant Br?nsted acid（H+）sites which exist in the DHBEA zeolite.When H+species react with the O atoms of carbonyl groups，the charge of C1 atom in cyclohexanone is 0.519，which is greater than that in the original molecule（0.405）.Thus，both the Br?nsted acid and the Lewis acid catalyzed BV oxidation mechanisms are proposed，as illustrated in Scheme 2.