Research On Preparation Of Mesoporous Silica-supported Metallic Oxides Or Noble Metals Catalysts And Their Catalytic Properties

Based on the catalytic application of ordered mesoporous silica(OMS), two routes were adopted in this paper to introduce active centers into the pore channels of OMS. On the one hand, iron or manganese heteroatoms were respectively doped into the silica framework, which was applied in the acid catalysis or redox catalysis. On the other hand, noble metal palladium or silver nanoparticles were respectively introduced into the silica channels after the surface modification of SBA-15, and the catalytic properties were demonstrated in the reduction reaction of aromatic nitro compounds by NaBH4.(1) In the process of post-synthesis of MSNs, it was simultaneously realized pore expansion and introduction of iron precursor Fe(acac)3, without damages of both morphology and integrity. The catalytic result of benzylation of benzene by benzyl chloride showed that Fe-MSNs were the suitable and ideal catalysts for this reaction. All Fe-MSNs samples demonstrated complete benzyl chloride conversion within 60 minutes at 333K and the selectivity to DPM over Fe-MSNs-3 with the highest iron content was up to 100%. When the temperature was set to 353K, the reaction was complete in a short time period of 8 min by Fe-MSNs-3 and the selectivity of DPM was over 95%. Moreover, stability of Fe-MSNs was also excellent depicted by recycling experiments for three times.(2) Based on Fe-MSNs, manganese doped MSNs was further studied. It was discovered that MSNs could maintain the nanoparticle morphology and ordered mesoporous structure even after hydro thermal and doping process. We successfully used Mn-MSNs to catalyse the oxidation of ethylbenzene and obtained a nice selectivity of main product of acetophenone.(3) By modification of SBA-15, aldehyde groups were grafted on the inner wall. Because of the reducibility of aldehyde groups, Pd/SBA-15 was successfully obtained by in situ reducing the precursor of Pd(OAc)2 in the channels. Also, process of modification and reduction did not destroy ordered structure of SBA-15. Using this Pd/SBA-15 catalyst in the reduction reaction of aromatic nitro compounds by NaBH4, we discovered that it had an excellent performance in this kind of reaction whether other groups in ortho-, para-or meta-position of nitro group. As a model reaction, reduction reaction of p-nitrophenol with the apparent first-order reaction rate constant kapp of 5.07X×10-1min-1, showed the catalytic effect was better than those reported.(4) Motivated by the experience of aldehyde groups grafting on the inner surface above-mentioned and the silver mirror theory, we successfully reduced silver-ammonia solution in the mesoporous channels. Introduction of silver did not destroy the order structure of SBA-15, either. From the result of the reduction reaction of p-nitrophenol by NaBH4 in the presence of Ag/SBA-15, it was proved that Ag/SBA-15 had a good catalytic performance.