Optimization of the catalytic cyclohexene oxidation with silica pillared clay incorporated with tungstovanadophosphoric acid using the central composite design – response surface methodology
摘要
Keggin type tungstovanadophosphoric acid H4PW11VO40.8 H2O (PVW) was prepared and impregnated on acid activated bentonite under mild conditions. In acidic solution, PVW was incorporated into a clay interlayer template using the sol–gel process. The catalysts were characterized by XRD, BET and FTIR analysis. The catalytic activity was evaluated in cyclohexene oxidation. Characterization analyses indicated that PVW was distributed more uniformly in the encapsulated sample compared to the impregnated sample. The most intriguing aspect about heterogenizing homogenous catalysts is that they can be recovered. The optimal conditions for cyclohexene oxidation by PVW/AAB and PVW-SC catalysts using H2O2 as oxidant. The influence of catalyst weight, method preparation of catalyst, reaction temperature, time and the molar ratio Cyclohexene/H2O2 were studied. To relate the process variables to the two responses, central composite design-based two-second order polynomial models were developed. The significant effects of parameters on each response were determined using the statistical analysis of variance. The significant variables influencing each response have been determined by the analysis of variance. According to the fitted models, predicted and actual responses typically are identical. Optimum conditions were estimated as 85.4 mg of catalyst, molar ratio of 2/1 (oxidant/cyclohexene) and impregnated catalyst (PVW/AAB) for preparation method under 72 °C for 10.2 h. The conversion and selectivity calculated by the model are 76% and 100%, they are close to the experimentally measured value 70% and 95% under the operating conditions quoted above.
Graphical abstract