Study Of The Adsorption Preparation For Eggshell-Type Pd,Pt Nano-Catalyst And Application

Supported noble metal catalysts were usually prepared by impregnation, ion-exchange process, coprecipitation, Sol-gel method and have been widely applied in the field of petrochemicals, fine chemicals and environmental catalysis for their high activity, easy separation and recyclable, etc.However, these methods often have the drawbacks of complicated procedures, non-green to environment and many influencing factors. It is well known these problems not only affect the overall performance of the catalyst, but also might caused the environmental pollution.In this thesis, a new method was proposed that the carrier was utilized to adsorb metal nanoparticles directly, which were obtained from the decomposition of Pt2(dba)3 (dba = dibenzalacetone) for the preparation of catalysts. This adsorption type method is able to prepare uniform particle size, narrow distribution range and structure controlable of high-performance catalysts. The adsorption Pt/C catalysts were characterized by transmission electron microscopy (TEM), inductive coupled plasma emission spectrometer (ICP) and X-ray photoelectron spectroscopy (XPS). The liquid phase hydrogenation of o-chloronitrobenzene (o-CNB) was used to test the catalytic properties of the catalysts and the corresponding hydrogenation dynamics was also first carried out. The adsorption Pd/C catalyst was also characterized by TEM,XRD and XPS, and showed extraordinary properties in Suzuki coupling reaction. The results are listed as follows:1,The characterization results showed that active constituent Pt on the Pt/C catalyst additives was in more electron-deficient state after the AC modified by Fe, and Pt nanoparticles distributed on the surface of the catalyst (10 times higher than average levels), forming an egg-shell structure. The results of catalytic hydrogenation of o-chloronitrobenzene showed that the best performance could be obtained when the dosage of Fe additive was doubles that of Pt. The conversion of o-CNB reached to 100% with the activity defined by TOF of 78 S-1 combined with the selectivity of 99.5% to corresponding aniline. Moreover, the selectivity can increased to 99.9% by adjusting the reaction conditions. In addition, macroeconomic factors (such as temperature, pressure,stirring rate) which could affect the dehalogenation were studied in detail. On the basis of low dehalogenation over the certain catalyst, a broad rule is proposed that the TOF whatever factors caused by decide dehalogenation rate essentially. In stability, the TTO of the catalyst can reach to 625,000 and the the main reason for the decreased activity was the aggregation of Pt nanoparticles. Meanwhile, the loss of active Pt was only 7%, which indicate the internal bonding strength between Pt nanoparticles and support is strong.2,A new reaction path was found that the hydroxylamine could be obtained directly from the hydrogenation of nitro-compound. Further kinetic studies demonstrated that the reaction rate is zero-order in o-chloronitrobenzene concentration and first-order with respect to hydrogen pressure,and the activation energy is 58.8 kJ/mol. The rate limiting step was adsorption of H2.3,The characterization results of Pd/C showed that the Pd with zero valent state loadad evenly in the carrier surface, of which particle size was in the range of 3-6 nm. This adsorption Pd/C catalyst showed extraordinary properties in Suzuki reaction. Under the conditions of 80 oC, and 0.5 h, the catalyst can catalyze Suzuki reactions of aryl bromide with coupling product yield of 98%. The coupling reactions of aryl bromides containing electron-withdrawing groups proceeded more efficiently than that of bromobenzene, while aryl bromides containing electron-donating groups needed a longer reaction time for completion. It can also catalyze o-chloronitrobenzene with yield of 64% in 1 h when the reaction temperature was 110 oC, and the yield can be higher than 90% with extending the reaction time.In conclusion, the adsorption method for preparing supported catalyst is simple and green, and tractable. Especially, the addition of Fe for the the Pt/C catalyst could significantly improve its catalytic performance for the selective hydrogenation of o-chloronitrobenzene which have showed the prospect of industrial application. Meanwhile,the Pd/C catalyst also exhibited very excellent catalytic effect for the Suzuki reaction of bromobenzene. It is believed this preparation method could be further extended to other supported metal catalysts preparation and corresponding reaction system.