| dc.description.abstract | Nanosized palladium catalyst has been reported to be a good catalyst for hydrogenation reaction. In this study, all the catalysts were prepared by incipient-wetness impregnation method and were tested for p-chloronitrobenzene (p-CNB) hydrogenation reaction. These catalysts were characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, energy dispersive spectrometer and X-ray photoelectron spectroscopy. The liquid-phase p-CNB hydrogenation reaction was carried out in the following condition: 298 K, 0.41 MPa partial pressure of H2, stirring rate 300 rpm in a batch reactor. The reactant was 0.2 M p-CNB methanol solution (2.54 g of p-CNB dissolved in 80 ml methanol) and 0.1 g catalyst was used to carry out the reaction. Samples were withdrawn in each 10 min. The solution was analyzed by a gas chromatography. In XRD pattern, only amorphous SiO2 peak was observed in all the catalyst, and no palladium or other metal peaks were observed because the particle sizes were too small to be detected. The TEM images showed that the average particle sizes of silica support on Pd/SiO2 were between 35 to 75 nm, and the average particle sizes of metal on Pd/SiO2 were about 2-4 nm. On the other hand, the average particle sizes of SiO2 on M-Pd/SiO2 (M = Ni, Pt, Ag and Fe) were around 50-125 nm, and the average particle sizes of metal on M-Pd/SiO2 were about 2-4 nm. From HRTEM images, Pd (111) was observed in Pd/samarium-silica and Pt-Pd/SiO2, the sizes of metal were consistent with TEM images. The XPS analysis indicates that adding platinum into palladium catalyst would decrease the content of Pd0 which plays a role of activity site for hydrogenation reaction on the catalyst surface. It’s the reason why the reaction rate decreases with the order : 1Pd/SiO2 > 0.2Pt1Pd/SiO2. The results of catalytic tests showed that all the three samples on Pd/SiO2 had high activity but very low selectivity for p-chloroaniline. Various bimetallic catalysts, such as Pt-Pd/SiO2, Ni-Pd/SiO2, Ag-Pd/SiO2 and Fe-Pd/SiO2 were tested. The results showed that only Pt-Pd/SiO2 could increase the selectivity of p-CAN and still kept high activity. | en_US |