Catalytic Hydrogenation Of Chloronitrobenzene Over Noble Metal Colloids

Polymer-stabilized metal colloidal catalysts are very important in the field of catalysis because of their fascinating catalytic properties. In this paper, the selective hydrogenation of CNB to CAN was chosen as model for the study of poly(N-vinyl-2-pyrrolidone)-stabilized Pt, Ru and Pt/Ru bimetallic colloids.Firstly, poly (N-vinyl-2-pyrrolidone)-stabilized platinum colloids (PVP-Pt) were prepared via the reduction of hexachloroplatinic acid in a refluxing mixture of water and alcohol (methanol, ethanol, n-propanol and n-butanol) by varying the amount of alcohol in the solvent. The metal colloids were characterized by transmission electron microscopy (TEM). Catalytic performance of the PVP-Pt colloids was tested by selective hydrogenation of m-CNB and p-CNB at 298 K and 0.1 MPa hydrogen pressure. The catalytic performance of the PVP-Pt colloids is dependent on the size of the nanoparticles. The selectivities to m-CAN and p-CAN decreased but the activities of the catalysts increased with the decreasing of the nanoparticles size.Secondly, the effect of metal complex on hydrogenation of o-chloronitrobenzene (o-CNB) over poly-vinylpyrrolidone stabilized ruthenium colloids (PVP-Ru) prepared by NaBH4 reduction containing boron species has been studied in methanol under 320 K and 4.0 MPa. The addition of metal complexes to the catalytic system improved the activity in different degree while the selectivity remained constant. Upon the addition of the complexes Fe(acac)3, Fe(8-HQ)²⁺, Fe(8-HQ)²⁺, the activities were increased to a factor of two. In the presence of Cu(en)2²⁺ or Zn(en)2²⁺, nearly 100% selectivity to o-chloroaniline (o-CAN) was achieved, with the activity 4 folds higher than that of the neat PVP-Ru colloids.Thirdly, PVP-stabilized platinum/ruthenium colloids (PVP-Pt/Ru) were prepared via the reduction of hexachloroplatinic acid and ruthenium (III) chloride in a refluxing mixture of water and ethanol. The morphology of bimetallic nanoparticles was characterized by transmission electron microscopy (TEM). Hydrogenation of m-CNB and p-CNB was carried out in a batch mode using hydrogen over the PVP-Pt/Ru bimetallic colloids at 298 K and 0.1 MPa hydrogen pressure. The product consisted of CAN, aniline and others during the reaction. The selectivity to m-CAN was increased to 94.71 % at 100 % conversion of m-CNB; the selectivity to p-CAN was increased to 99.84 % at 100 % conversion of p-CNB. It was observed that the catalytic performance of the PVP-Pt/Ru colloids is dependent on the compositions of the bimetallic colloids. The selectivity to CAN decreased but the activity of the catalyst increased with the increasing proportion of platinum in Pt/Ru colloids.Finally, the effect of Fe3+, Co²⁺, Ni²⁺ and Sn²⁺ metal ions on hydrogenation of chloronitrobenzene (CNB) was studied. The catalystic reactions were carried out in a batch mode using hydrogen over the PVP-4Pt/1Ru bimetallic colloids at 298 K and 0.1 MPa hydrogen pressure. The selectivity to CAN and the activity of the catalyst were increased as Fe3+, Co²⁺, Ni²⁺ and Sn²⁺ metal ions added in the reaction system. The addition of metal ions to the catalytic system improved the activity and selectivity in different degree (except Sn²⁺ selective reduction of m-CAN), The different metal ions have different effects. On the addition of the Sn²⁺ to the hydrogenation of o-CNB, the selectivity to o-CAN was increased from 93.08 % to 100 %, while the activity increased from 0.059 molH2/(molM·s) to 0.112 molH2/(molM·s); On the addition of the Co²⁺ to the hydrogenation of m-CNB, the selectivity to m-CAN was increased from 84.01 % to 92.42 %, while the activity increased from 0.098 molH2/(molM·s) to 0.123 molH2/(molM·s); On the addition of the Sn²⁺ to the hydrogenation of p-CNB, the selectivity to p-CAN was increased from 92.05 % to 99.83 %, while the activity increased from 0.067 molH2/(molM·s) to 0.205 molH2/(molM·s).