Study Of Assembled Pt/C Catalyst For The Catalystic Performance

Supported metal catalysts were usually prepared by impregnation,sol-gel, ion-exchange and have been widely used in the filed of chemicalsand catalysis for their high activity, easy separation and recyclablity, etc.However, these methods often have the drawbacks of complicatedprocedures, non-green to environment and other influencing, which affectthe overall performance of the catalyst. Besides, deactivation andreactivation of the supported catalyst are also vital impact, especially theability of anti-poisoning of sulfur.In this dissertation, the carrier was utilized to adsorb metalnanoparticles directly, which were obtained from the decomposition ofPt2（dba）3for the preparation of catalysts. Supported metal catalyst withuniform particle size, narrow distribution range and structurecontrollablility can be obtained. Modification of transition metal cationsto assembled Pt/C catalyst was studied. The surface structure, the surfaceelectronic state, and the spread of Pt nanoparticles distribution werecharacterization by TEM, XRD and XPS, respectively.The liquid phase hydrogenation of o-chloronitrobenzene was used totest the catalytic properties of the catalyst. Meanwhile, the effect ofauxiliaries and stability of the catalysts were also discussed. Main points of this dissertation were listed as following:1. The characterization results showed that the particle size of Pt/Ccatalysts prepared by adsorption was uniform. And the catalyst showedhigher performance of o-chloronitrobenzene compared with Pt/C catalystprepared by immersion. In the hydrogenation of cinnamaldehyde, Pt-Fe/Cshows high selectivity of cinnamyl alcohol, while Pt/C prepared byimmersion is inclined to exhibit high selectivity of phenylpropyl aldehyde.This is because that with the addition of iron, the surface electronics ofcatalyst were changed, which is benefit for the activation of C=O.2. The results of p-CNB hydrogenation showed that the Pt-Fe/Ccatalyst performed better than the commercial catalysts. The stableexperiment results showed that the catalysts can keep high conversionand selectivity after11recycling times, the stability is better thancommercial catalysts. Based on the results of the catalyst characterizationand reaction conditions, the structure of support collapsing is the mainreason of the catalyst deactivation. Besides, some byproducts adsorbed inthe surface of the catalyst, which would cause the decreasing of activesite of the catalyst, could be reactivated through the rinsing by acid.3. The results of catalytic hydrogenation of o-CNB showed that thePt-Fe/C catalysts exhibited best anti-poisoning performance of sulfur.When the dosage of Co additive was doubled that of Pt: The conversionof o-chlornitrobenzene reached to99.26%from34.4%, and the selectivityreached99%in the first30min. However, it would not improve thecatalysts anti-poisoning ability when adding Co³⁺ to the reaction systemdirectly. This indicated that the poison performance of catalyst wasattributed by the synergistic reaction between Fe and Co. After modifiedby Fe and Co, the surface of the metal catalyst utilization, the masstransfer resistance and electronic effect were improved, which enhancedthe adsorption between the carried and Pt atom. As a result, the stability of the catalyst was improved. In addition, the limited concentration ofthiophene in the raw material was300ppm, otherwise, the activity of thecatalyst would decrease dramatically.In conclusion, assembled Pt/C catalyst prepared by the method ofadsorption not only exhibited some inherent advantages such assimplifying the procedures, catalytic structure controllability, but alsoshowed excellent activity and selectivity on the hydrogenation ofchlornitrobenzene. The catalysts modified by Fe and Co presentedpotential industry prospect because of the good catalyst stability andanti-poisoning ability. This might provid new opportunities andalternatives of great interest to other kinds of liquid hydrogenationreactions.