Preparation Of Mesoporous Hollow SiO₂ Spheres Loading With Mn-N-C For Selective Oxidation Of Ethylbenzene

Catalytic technology plays a key role in the fields of energy conversion, material synthesis, environmental protection and human health. However, with the running out of oil resource in the definite future and the growing demand of ecological and environmental protection coming from the public, it is urgent to build environmental-friendly chemical processes. In order to achieve a virtuous process with high efficiency, low carbon emission and environmental friendly, the research and development of novel catalysts with high catalytic performance is of great importance.Transitional metal porphyrins are macrocyclic compounds. And their structures contain transition metal, carbon and nitrogen, which makes them suitable precursors for one-step preparation of transition metal-carbon-nitrogen materials. However, the direct calcination of theses precursors generates catalysts with small surface areas, and the metal centres are prone to aggregate into large-sized particles, which may not benefit to enhance their catalytic activity. Hollow mesoporous silica is a good carrier with large surface areas, which can also be easily prepared and modified. Considering the advantages of transitional metal porphyrins and hollow mesoporous silica, we propose the preparation of hollow mesoporous silica supported transition metal manganese nitrogen carbon material catalyst with manganese porphyrin as precursors of Mn-N-C sites. The specific researches are listed as follows:1. Hollow mesoporous silica nanoparticles supported Mn-N-C catalyst has been prepared via hard-template method. With manganese porphyrin as Mn-N-C precursor, iron oxide nanoparticles as hard template, Mn-N-C@SiO2 catalyst with Mn-N-C loading on the internal surface of hollow mesoporous silica microspheres has been prepared. The catalytic performance of Mn-N-C@SiO2 has been investigated via the selective oxidation of ethylbenzene with molecular oxygen as oxidant, and solvent-free conditions. The results show that the Mn-N-C@SiO2 catalyst has regular hollow mesoporous morphology with large specific surface area (673.2 m2g-1) and total pore volume (0.58 cm3g-1). And Mn-N-C sites are evenly distributed on the inner wall of the hollow sphere. Mn-N-C@SiO2 displays better catalytic performance and stability. Moreover, the turnover frequency is higher than that of pure Mn-N-C (612.8 h-1) obtained by pyrolysis of manganese porphyrin.2. Hollow mesoporous silica nanoparticles with Mn-N-C integrated in the framework have been prepared via self-template method (Mn-N-C-x@SiO2). After modified with APTES, manganese porphyrin can be doped into the solid mesoporous silica microspheres in the sol-gel process. After that, the solid product incubates in water. Then, hollow mesoporous silica microspheres with uniform distribution of Mn-N-C in the framework are obtained after calcination in N2 atmosphere. The content of Mn-N-C in the catalyst structure can be adjusted by changing the amount of the modified manganese porphyrin(x= 0.01 g,0.02 g,0.04 g, 0.06 g). Mn-N-C-x@SiO2 displays regular hollow mesoporous spheres with high specific surface area and total pore volume. Besides, Mn-N-C-x@SiO2 exhibits relatively high catalytic performance and stability. When the amount of manganese porphyrin is 0.01 g, the turnover frequency of ethylbenzene of Mn-N-C-001@SiO2 is 2427.6 h-1.3. Hollow mesoporous silica nanoparticles supported Mn-N-C catalyst (Mn-N-C-x@HS(IM)) has been prepared via impregnation method. The results show that the Mn-N-C is mainly located on the inner wall of the hollow mesoporous silica spheres. The amount of Mn-N-C in the catalyst can be adjusted by the amount of manganese porphyrin used during the impregnation process (x= 0.005. g,0.01 g,0.02 g,0.04 g,0.06 g). Mn-N-C-x@HS(IM) exhibits relatively high catalytic performance and stability. When the dosage of manganese porphyrin is 0.005 g, the. turnover frequency of ethylbenzene of Mn-N-C-0005@HS(IM) is 1380.7 h-1. In addition, the results also suggest that the hydrophobicity of the catalyts is beneficial to enhance the catalytic performance.