Preparation Of Functional Graphene And Its Application As A Catalyst

Graphene sheets, two-dimensional one-atom-thick layers of sp2-bonded carbon, have attracted tremendous attention as its discovery. It has a large specific surface area (2630m2·g-1), unique planar structure, essentially infinite possibilities for modification and functionalization of carbon backbone and hydrophobicity on the surface merit attention for application as solid catalyst by functionalization or an ideal substrate for supporting catalytic nanoparticles. However, the applications for the graphene in the field of catalytical chemistry are rarely reported.In this thesis, a single-layer structure of graphene oxide was prepared by modified Hummers method. Sulfonated graphene and Pd-decorated graphene nanosheets, two different types of catalysts based on graphene, were respectively obtained.The analysis results of FT-IR, elemental analysis, XRD, SEM and TEM showed that graphene oxide bearing with-COOH,-OH and-SO3H was successfully prepared, and it could disperse well in polar solvents.Sulfonated graphene, a highly active solid acid catalyst, was prepared by sulfonation. FT-IR, XPS and elemental analysis showed that-SO3H bonded to the graphene sheets firmly by carbon-sulfur bond. The catalyst was used to catalyze the hydrolysis of cellobiose and soybean isoflavone. Experimental results showed that the sulfonated graphene had a excellent catalytic activity. Under the preliminary optimized condition, the conversion of cellobiose and the yield of glucose was40.5%and37.2%in the hydrolysis of cellobiose, and the conversions of three kinds of isoflavone glycosides are94.3%,92.1%, and88.8%, the yields of the corresponding aglycones are69.6%,60.6%, and58.8%in the hydrolysis of soybean isoflavone, respectively. Compared with other commercial solid acid catalysts such as zeolite HZSM-5and macroporous resin NKA-9, the activity of sulfonated graphene was remarkably higher, which was similar to that of0.2mol·T-1sulfuric acid. The catalytic mechanism of sulfonated graphene has been studied in this thesis. The enhanced hydrolytic catalysis of the sulfonated graphene can be explained as the area of adsorption which is built by hydrophobic graphite structure and hydrophilic functional groups bearing on the planes and edges of graphene. N2adsorption, XPS, XRD and TEM were used to investigate the palladium decorated-graphene nanosheets. The results showed that palladium species dispersed monolayer on the support. The average diameter of palladium in the three palladium decorated-graphene nanosheets catalysts Pd2+@GNs, Pd@G-SBH and Pd@G-EG was4.8,6.7and18.2nm, respectively. The palladium loading amount were7.2and7.5wt%in Pd@G-SBH and Pd@G-EG, respectively. The performance of the catalysts was tested in the selective hydrogenation of benzene ring. The experimental results showed that Pd@G-SBH and Pd@G-EG had a good catalytic activity to the hydrogenation of benzene ring, which were better than commercial Pd/C. Pd2+@GNs did not exhibited similar catalytic activity, which can be explained abscission of palladium species during the reaction process.The influence of Lewis acid-supported Pd catalyst and base-supported Pd catalyst to the selectivity of the hydrogenation of benzene ring were studied. The experimental results showed that non-polar solvents should be used as reaction solvent in Lewis acid-supported Pd catalyst since the polar solvents may inhibit the hydrogenation reaction. Lewis acid can be beneficial to the selectivity of cyclohexanone in the hydrogenation of phenol, but cannot be beneficial to the selectivity of diketone in the hydrogenation of resorcinol and pyrocatechol because of the dihydroxyl structure when react with Lewis acid. The results of base-supported Pd catalyst in the hydrogenation of resorcinol and pyrocatechol showed that the conversion of resorcinol and1,3-cyclohexanedione yield were99.9%and99.9%catalyzed by Pd@G-SBH, and also can get the similar results in hydrogenation of pyrocatechol.