Study On Silica Supported TEMPO/NO_x Catalytic Systems And Their Application In Selective Oxidation Of Alcohols

Selective oxidation of alcohols to their corresponding carbonyl compounds is wildly applied in synthesis of organic intermediates and fine chemicals.2,2,6,6-tetramethylpiperdine1-oxyl (TEMPO) has become more and more attractive for which it has not only expressed efficient performance under mild conditions, but also having a substrate universality when using in selectively oxidize various kinds of alcohols into their corresponding aldehydes and ketones.In our work we used TEMPO as major catalyst and NOx as co-catalyst to realize aerobic alcohol oxidation. We developed three novel heterogeneous catalytics, SA-TEMPO/NOx, SB-TEMPO/NOx and S-4-OH-TEMPO/NOx All of them has expressed efficient performance in the selective oxidation of alcohols under mild conditions. The separation of products and catalysts also very simple.Silica-gel is silica oxide material with abundance of surface Si-OH, which can be used to immobilized TEMPO. In addition, the pores, cracks and also the immobilized TEMPO of the Silica-gel can be used to adsorb NOx. Thus, when the silica supported TEMPO adsorb NOx, we got gas-solid full unity catalysts. Through investigating the effect of the silica particle size and pore size on the preparation of catalyst, we finally got the conclusion that the silica which with10nm pore size and30-60μm particle size expressed good effect.SA-TEMPO/NOx was prepared by60μm-10nm silica, in the present of0.5g SA-TEMPO/NOX, at ambient temperature and pressure,1mmol benzyl alcohol was translated to benzaldehyde within4h with100%conservation and100%selectivity, it also can be reused. While SB-TEMPO/NOx was prepared by60μm-10nm silica and it could finish the same oxidation in2h under same conditions.Furthermore, we also used the sol-gel method to prepare S-4-OH-TEMPO/NOx.4-OH-TEMPO was dissolved in methanol, and then TEOS was added, Si:CH3OH=1:1.5. After that,0.5mL HCl (38%) was added dropwise to accelerate methanolysis and condensation of TEOS. when the solution aging into solid, the obtained silica was washing and griding, the size of silica is through80mesh sieve, thus we got S-4-OH-TEMPO. Then absorb NOx we got S-4-OH-TEMPO/N0x In the presence of0.5g S-4-OH-TEMPO/NOx.1mmol benzyl alcohol was completely translated to benzaldehyde in8h under mild conditions.Elemental analysis. FT-IR, nitrogen adsorption-desorption, NOx-TPD. SEM and XRD were employed to study the catalyst. GC and GC-MS were used to monitor the reaction process. Based on the characterization results and testing data, we also gave proposed alcohol oxidation machinsm system by this heterogeneous catalyst.