Study On Catalytic Activity Over Nano Ni And NiB Catalysts Prepared In Ionic Liquids

It is a novel subject to prepare nano catalysts in ionic liquids. Nano metal Ni andamorphous alloy NiB catalysts were prepared with ionic liquid as a reactionintermediate. The styrene hydrogenation and toluene oxidation were used as probereactions to evaluate the catalytic activity. Some basic studies about the greatdifferences in the appearance and structure between the two kinds of catalysts, and themechanism of stabilize the nano particles were executed in the thesis.One kind of catalyst was prepared by chemical reduction method in the aqueoussolution, named Ni, NiB; the other kind of catalyst was prepared in the solution of ionicliquid and anhydrous alcohol, named Ni-IL, NiB-IL.The studies on the reaction of styrene hydrogenation and toluene oxidation wereexecuted in the self-made high pressure reactor and Gas Chromatography equipped witha FID detector. The results of hydrogenation revealed that the prepared two kinds ofcatalysts all have the catalytic activity, while the catalysts prepared in ionic liquids havea significantly higher catalytic activity compared with that prepared in conventional way.The catalytic activities were compared as follows (use the styrene conversion andphenylethane yield to evaluate the activity) : the conversion of styrene: Ni: 32.2%,Ni-IL: 57.1%; NiB: 40.8%, NiB-IL: 72.6%; the yield of phenylethane: Ni: 42.3%,Ni-IL: 66.8%; NiB: 43.6%, NiB-IL: 84.5%. The catalytic activities of oxidation werecompared as follows (use the toluene conversion and benzoate yield to evaluate theactivity): the conversion of toluene: Ni: 19.6%, Ni-IL: 31.8%; NiB: 17.4%, NiB-IL:27.4%; the yield of benzoate: Ni:22.3%, Ni-IL: 37.9%; NiB: 20.7%, NiB-IL: 34.1%.The great differences of catalytic activity between the two kinds of catalysts indicatedthat the ionic liquids might play a key role to stabilize the nano catalysts and prevent theaggregation of active nano particles. Some basic studies of the different stable abilitiesin the different kinds of ionic liquids (including [bmim] BF₄,[bmim] PF₆,[mim] BF₄)were also executed in this work. The results revealed that the catalyst prepared in[bmim] BF₄ has the greatest catalytic activity. The reason was may be the ionic liquid[bmim] BF₄ has a bigger viscosity and stronger ability of coordination.The catalysts were characterized by XRD, TEM, FT-IR, UV-Vis and TG-DSC. The results of XRD and TEM revealed: compared with the aggregate Ni catalyst,theNi-IL has a better distribution and appearance,only three diffraction peaks wereobserved in the range of 2θ=20°～80°,which corresponding to the diffractions ofthree crystal planes (111),(200),(220) belongs to the face centered cubic structure.While for the NiB-IL,no sharp crystal peak was observed except the characteristic peakof amorphous around 2θ=45°,which has a wider structure disorder,a betterdistribution and appearance compared with the NiB catalyst. The results of FT-IR,UV-Vis and TG-DSC further indicated the existance of ionic liquid layer around thenano catalysts' surface. On one hand,the ionic liquid absorbed catalysts existed in aform of protective layer to prevent the nano particles aggregation. On the other hand,the high viscosity ionic liquid worked as a good medium made the nano particles have auniform dispersion.