Study Of Assembled PT-Fe Nano-Catalyst For The Selectivity Hydrogenation

Supported metal catalysts have been widely used in the hydrogenation, dehydrogenation and reforming catalytic reactions because of easy recyclable and reusable. Supported metal catalysts are usually prepared by conventional impregnation method. However, this method has some drawbacks: complicated procedure, non-green to environment, many influencing factors. It is still difficult for those catalysts to maintain high unity of activity, selectivity and stability at the same time.In this thesis, the carrier was utilized to adsorb metal nanoparticles directly for the preparation of catalysts. Soluble metal nanoparticles were extensively studied around the world, currently. Supported metal catalyst with uniform particle size, narrow distribution range and structure controllable can be obtained by the decomposition of organometallic precursors such as Pt2(dba)3 using a reducing gas such as hydrogen gas in a solvent and stabilized by the solvent. Modification of transition metal cations to assembled Pt/C catalyst was studied in selective hydrogenation of o-chloronitrobenzene (o-CNB) and cinnamaldehyde to test the catalytic properties of the catalysts. The assembled Pt-Fe/C catalysts were characterized by transmission electron microscopy (TEM), inductive coupled plasma emission spectrometer (ICP) and X-ray photoelectron spectroscopy (XPS). The results are listed as follows:1. The characterization results showed that more of Pt atom was distributed on the surface of the catalyst after the catalyst modified by Fe (Compared with traditional methods), forming a core/shell structure. There is no doubt that core/shell structure would offer more active sites for the hydrogenation and are also conducive to reducing the mass transfer resistance. On the other hand, the existence of Fe in the form of Fe2O3 would further prompt Pt particles in the electron-deficient state, to substantial increase in the hydrogenation catalyst activity, selectivity and stability.2. The results of o-CNB hydrogenation showed that the best performance could be obtained when the dosage of Fe additive was doubles that of Pt: conversion of 100%, TOF of 78 S-1, selectivity of 99.5%. Based on experimental results, the modification mechanism of Fe could be the interaction between Fe and -NO2 group of the substrate increased the polarity of N=O bond and accelerated the hydrogenation of nitro group. Because of the same reason, the polarity of C-Cl bond was decreased and the strength of C-Cl bond was increased,so that the dehalogenation reaction was greatly inhibited. These outer active sites not only increase the adsorption probability of reactant molecules for speeding up the reaction rate, but also greatly shorten the residence time of the reaction species which are responsible for avoiding the deep hydrogenation. In stability, the TTO can reach to 625,000 and the main reason for the decreased activity was the aggregation of Pt nanoparticles. Meanwhile, the loss of active Pt was only 0.6%, which indicated that strong combination with the carrier AC.3. The hydrogenation for different kinds of aromatic nitrocompounds was studied on the assembled bimetallic Pt-Fe/C catalyst, including: nitrobenzene, halonitrobenzene, nitrotoluene, 2,4-dinitrotoluene, 4-nitroanisole and so on. Majority of these aromatic nitrocompounds had yields more than 96% in the liquid phase hydrogenation reaction. Apparently that this catalyst could be widely used for many hydrogenation reaction.Those might be provided new opportunities and alternatives of great interest for this kind of hydrogenation reduction reaction.4. The promoting effect of several metal promoters on assembled Pt/C catalyst for the liquid phase hydrogenation of cinnamaldehyde has been investigated.The conversion of cinnamaldehyde and the selectivity to cirmamyl alcohol is 87.2%and 80.41%, respectively, over Pt-Fe/C catalyst after reaction 2.5h. Experimental results show that adding small amount of promoters can obviously affect the catalytic properties. With the assistant of electron-deficient Fe to adsorb oxygen and the space block of benzene chain, C=O double bind can be adsorbed and activated by the active site of metal Pt.In conclusion, it is clear that assembled bimetallic Pt-Fe/C catalyst was exhibits good catalytic properties on liquid phase hydrogenation reaction, and this catalyst preparation process is simple, easy to operate, high reproducibility and controlled. These supported metal catalysts can be potentially applied in several multi-phase reactions to produce the target products with high conversion and selectivity.