《Table 6 Energy difference among three hydroxyhexanoic acid adsorption models》

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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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As shown in Table 5，the Lewis acid species in Al atoms do not have the activation effect on enhancing the nucleophilic attack capability of H2O2 molecules.Here，the adsorption models of 6-hydroxyhexanoic acid molecules on the trigonal Al sites are calculated，as illustrated in Figure 5.There are three O atoms in one6-hydroxyhexanoic acid molecule，which can possibly be absorbed by trigonal Al species via the acceptor-donor interaction between Al sites of active sites and these O atoms.It is found that the Al…O bond distance in model（b）is shorter than that of other two models（a）and（c），which suggests that model（b）is the most possible one for further oxidation reaction.Table 6 gives the corresponding adsorption energy for these three models.When the adsorption energy of model（b）is defined as 0，then that of models（a）and（c）is 74.46 kJ/mol and 32.23kJ/mol，respectively.Therefore，we can infer that the O atom of carbonyl group is apt to be adsorbed on trigonal Al sites.And in model（b），the charge of C atom of terminal C-OH group is-0.180，which is smaller than that in the original molecule（0.054）.It is indicated that the terminal C-OH groups cannot be activated to accept the nucleophilic attack by H2O2 molecules.Thus，according to the above-mentioned results，the reason why few adipic acid produced in DHBEA zeolite catalyzed system can be well explicated.