Selective Hydrogenation Of Acyl-substituted Nitrobenzene Over Supported Nano-platinum Catalysts

Acyl-substituted anilines are an important class of food raw materials and organic synthesis intermediates, which have been widely used in the fields of spices, dyes,pharmaceuticals, food, agricultural chemicals, etc. The acyl-substituted anilines are mainly synthesized by reduction of acyl-substituted nitrobenzene. The synthesis of acyl-substituted aniline from acyl-substituted nitrobenzene by catalytic hydrogenation gradually received much attention owing to its advanced process, high yield and friendly to environment, etc. At present, the catalytic hydrogenation of acyl substituted nitrobenzene to acyl-substituted aniline mainly used Raney nickel as catalyst, which show low catalytic activity and poor selectivity. There is an urgent need to develop a new high-performance catalyst.In this dissertation, the selective hydrogenation of acyl-substituted nitrobenzene over titanium dioxide supported Pt(Pt/TiO2) catalyst was studied. It was found that the Pt/TiO2 catalyst showed excellent catalytic performance for the selective hydrogenation of 3-nitroacetophenone(3-NAP) to 3-aminoacetophenone(3-AAP). Pt loading, support and catalyst preparation conditions have significant influence on its catalytic performance. Anatase TiO2 calcined at 700℃ as support, 0.3 wt% Pt/TiO2 prepared by an impregnation, H2 reduction and washing thoroughly with distilled water after H2 reduction, showed the best catalytic performance. The selectivity to 3-AAP can be up to100% at complete conversion of 3-NAP over the 0.3 wt% Pt/TiO2 under mild conditions(303 K 、 1.0 MPa H2) and the catalyst can be reused for many times. Reaction temperature, H2 pressure and reaction solvent have a pronounced effect on its catalytic performance. Polar solvent(such as methanol), higher reaction temperature and H2 pressure are favorable for 3-NAP hydrogenation to 3-AAP over the 0.3 wt% Pt/TiO2.BET, XRD, TEM and XPS were used to characterize the Pt/TiO2 catalysts. The results revealed that the Pt particles in the Pt/TiO2 were highly dispersed on the TiO2,and there were TiOx(x < 2) species on the TiO2 surface. The Ti Ox(x < 2) species not only can activate N=O bond which becomes highly susceptible to hydrogen attack, but also can donate electrons to the Pt particles in the Pt/TiO2, which made the Ptnanoparticles in the Pt/TiO2 electron-rich state, and the electron-rich state of the Pt particles supported on the TiO2 support, would strengthen the extent of electron from the Pt particles to the carbonyl in 3-NAP, which would suppress the carbonyl hydrogenation of 3-NAP. This may be responsible for the excellent catalytic performance of Pt/TiO2 catalyst for 3-NAP hydrogenation to 3-AAP.