Preparation Of Polymer-Stabilized Metal Nanoclusters And Their Catalytic Properties For Hydrogenation Of O-Chloronitrobenzene

Metal nanoclusters in the range of 1~10 nm are very important in academia and industry, especially in the field of catalysis. However, the surfactant-stabilized metal clusters are not stable and intend to agglomerate during reaction even under very mild conditions. Thus, the polymer-stabilized metal clusters are extremely important for their catalytic use. Some researchers have reported novel performances of nanoscale monometallic and bimetallic clusters in many reactions.Hydrogenation of halonitroaromatics to the corresponding haloanilines is important in the chemistry of dyes, drugs, herbicides and pesticides. The traditional routes for their production involve Bechamp's procedure, corresponding haloanilines were obtained by reducing halonitrobenzene with hydrogen in situ produced by hydrochloric acid and powdered iron. Because of the low yield of corresponding haloanilines and the environmental impact associated with the use of hydrochloric acid in Bechamp's reaction, selective hydrogenation of halonitroaromatics over a metal catalyst such as palladium, platinum and Raney nickel, is now preferred. This thesis focuses on the following aspects:Firstly, Poly(N-vinyl-2-pyrrolidone)-stabilized palladium colloids (PVP-Pd) were prepared by reducing H2PdCl4·nH2O in methanol and water mixed solvents. The metal colloids were characterized by TEM. It was observed that the diameter of PVP-Pd nanoparticles was increased when the volume ratio of methanol-water was increased; The mean diameters of the Pd nanoparticles prepared range from 4.1 nm to 7.0 nm, and standard deviations range from 0.81 nm to 1.64 nm. PVP-Pd with smaller sized and narrow size distribution was obtained when V(CH3OH)/V(H2O) is 1:1; different particles with wide size distribution of PVP-Pd could be obtained when V(CH3OH)/V(H2O) are 3:7, 7:3 or 9:1, and the particles appear to be aggregation.Secondly, palladium-platinum bimetallic colloids (PVP-Pd/Pt) were prepared by methanol reduction of the corresponding metal salts in methanol/water (1:1, v/v). The obtained metallic colloids were characterized by transmission electron microscopy. It was observed that the particles of PVP-Pd/Pt bimetallic colloids have average diameters ranging from 2.5 to 3.5 nm. The standard deviations of the bimetallic nanoparticles range from 0.6 nm to 0.9 nm. The core-shell model particles, with Pt cores, would be most likely formed in the PVP-Pd/Pt colloids.Thirdly, palladium colloids were used as catalysts for the selective hydrogenation of ortho-chloronitrobenzene in methanol at 303 K under 0.1 MPa of hydrogen. It was observed that the activity of PVP-Pd colloids was different when the particle size was different. The results allow us to conclude that catalytic properties of PVP-Pd colloids were dependent upon particle size and size distribution of PVP-Pd. The activity of PVP-Pd colloid with smaller size (4.7 nm) and narrow size distribution reached 0.923 mol H2/mol Pd·s.Finally, platinum colloids were used as catalysts for the selective hydrogenation of ortho-chloronitrobenzene in methanol at 303 K under 0.1 MPa of hydrogen. The influence of reaction temperature, catalyst concentration, substrate concentration on the activity and selectivity has been investigated. Under the conditions of 30°C, PH2=0.1 MPa, the conversion of o-chloronitrobenzene reached 92.3 % and the selectivity for o-chloroaniline was 76.9 %.