Designed Synthesis Of Polyacids-based High-performance Selective Oxidation Catalysts

Oxidation reactions, especially for the selective oxidations, as an important branch of organic chemical industry, play an important role in newborn substance and reciprocal transformation, and get excellent prospects and significance in modern chemistry. As homogeneous catalysis system is gradually replaced by heterogeneous catalyst, the problems such as easily active component loss, difficult recycling process and so on have been solved by heterogeneous catalysis system. Also, together with other advantages, such as mild reaction conditions and simple technological process, heterogeneous catalysis system have obtained more focus and study in organic catalysis. Among them, the appearance of mesoporous molecular sieve materials(SBA-15, MCM-41, etc), especially mesoporous material SBA-15, known as a good carrier in catalysis system, provide a broad prospect for heterogeneous catalysis.This article firstly prepared the mesoporous material ZrSBA-15, then according to the layer-by-layer loading strategy, the intermediate pentaethylenehexamine(PEHA) and active component PW12 have successfully loaded to the internal of mesoporous material ZrSBA-15 step by step, successfully synthesized a polyacids-based high-performance selective oxidation material, named as PW12/PEHA/Zr SBA-15. The experimental results determined that, this solid catalyst PW12/PEHA/Zr SBA-15 exhibited excellent catalytic performance towards the selective oxidation benzaldehyde to benzoic acid and benzyl alcohol to benzaldehyde. Through the examination of experimental parameters such as reaction time, reaction temperature, molar ratios and the amount of catalyst and so on, in the first reaction, the yield of benzoic acid could reach to 99.7%, and more importantly, after 10 reaction cycles, the yield of benzoic acid could also reach to 90%. In the selective oxidation benzyl alcohol to benzaldehyde, the conversion of benzyl alcohol could reach 84.7%, as well as the selectivity of benzaldehyde 99%, in addition, this excellent results were maintained even after five reaction cycles. To sum up, these oxidations fully demonstrated the high catalytic activity and stability of this solid catalyst PW12/PEHA/ZrSBA-15. In order to demonstrate the uniform structure of this catalyst, a variety of characterization methods were used to explain it.However, because of the big structure of PW12, which could occupy bigger space, and as a result, some structure autolysis phenomenon might occurr during the high-temperature and long-time reactions, and led to the decrease of the catalytic effect. Based on which, we prepared the smaller structure molecule H3PW4O24(PW4), and use the same method, load it to the support PEHA/Zr SBA-15, labelled as PW4/PEHA/Zr SBA-15. In the epoxidation reaction of cyclohexene to adipic acid, this catalyst exhibited excellent catalytic performance. Under the optimal conditions, the conversion of cyclohexene could reach to 100%, and the yield of adipic acid could reach 90.9%, more importantly, during five reactions, the catalytic activity could also maintain at a stable level, fully illustrated the stability of this catalyst.Through the excellent performance of mesoporous solid acid catalyst to this oxidation reactions, we are determined to say that this catalyst has a board application prospect in the organic oxidation reactions.