Study Of Assembled Pt、Pd Nano-catalyst For The Selectivity Hydrogenation

Supported noble metallic catalysts were widely used in hydrogenation,dehydrogenation and reforming because they were very important in thefields of the petroleum, chemical, medicine, pesticide, food,environmental protection, energy and electronic. Supported noblemetallic catalyst were usually prepared by the method of impregnation,however, it is limited by complicated procedure, susceptible and unableto unity among high activity, selectivity and stability. Besides, the noblemetals were existed in the formation of ion, which could enter the innerhole of the carrier easily, leading the low atomic utilization of noblemetal.In this dissertation, a new method was proposed that the carrier wasutilized to adsorb metal nanoparticles which were obtained from thedecomposition of Pt₂（dba）₃（dba=dibenzalacetone） and Pd₂（dba）₃for the preparation of catalysts. This adsorption type method was able to prepareuniform particle size, narrow distribution range and structure controllableof high-performance catalysts. After modified by the second metal, alkaiadditives and carrier, the assembled catalysts were applied in selectivehydrogenation of cinnamyl aldehyde （CAL） and tetrahydrophthalicanhydride （THPA）. The assembled Pt and Pd catalysts were characterizedby Transmission electron microscopy （TEM）, X-ray photoelectronspectroscopy （XPS）, and X-ray diffraction （XRD）. The results are listedas follows:1、 The TEM results showed that the mean nanoparticles size of Pt inthe assembled Pt/C catalysts and the catalysts prepared by the method ofimpregnation were1.7nm and5.4nm, respectively. Pt-Fe bimetalclusters were emerged on the surface of AC and the Pt nano-particlesfilled out larger （2.1nm） after modified by Fe. XRD results showed thatprecious metal nanoparticles were existed in the formation of crystallinestructure. XPS results showed that both Pt and Pd were zero valences.The majority of Pt atoms were distributed on the surface of the catalyst.There is no doubt that this would offer more active sites for thehydrogenation and were also conducive to reducing the mass transferresistance. Therefore, it would further prompt Pt particles to substantialincrease in the hydrogenation catalyst activity and selectivity. 2、 The results of cinnamyl aldehyde（COL） selective hydrogenationshowed that it was beneficial to the activated adsorption of C=O at lowtemperature, while C=C was activated at high temperature. The additionof Fe, Ce and Zn could improve the selectivity of cinnamon alcoholeffectively. The Pt-1.5%Fe/C^b（400℃）catalyst exhibited the highestactivity and selectivity at60°C,2.5h, and4.0MPa H₂. The conversionfor CAL was93.4%, and the selectivity of COL was91.3%. This couldbe explained that Pt-Fe metal clusters were beneficial to activationadsorption of C=O. So the selectivity of COL was improved greatly.Besides, using FeCl₃as presoma, the selectivity of COL was high, thanksto Cl could inhibit the formation of acetals.3、 The hydrogenation of THPA was studied on assembled Pd catalysts,which were supported on different carriers. The results showed that theselectivity of hexahydrophthalic anhydride （HHPA） was improvedobviously on assembled Pd/Fe₂O₃. Unfortunately, the conversion was lowbecause Fe₂O₃did not have abundant micropore. Compared to Pd/Cprepared by impregnated method, the assembled Pd/C catalysts showsuperior catalytic performance on THPA with the selectivity of HHPA upto99.6%, while ring opening occur on Pd/C prepared by immersionmethod with the selectivity of HHPA91.1%. 4、 In the study of the hydrogenation of THPA on assembled Pd/Ccatalyst. The results showed that the assembled Pd/C catalyst exhibitedthe highest activity and selectivity at85°C,2.5h, and3.0MPa H₂. Theconversion of THPA was100%, and the selectivity of HHPA was99.6%,no ring opening and coupling reaction were observed. But, the catalyticactivity was decrease, accompanied the ring opening and couplingreaction were occurred when the supporter was modified by alkalineadditives. The selectivity of HHPA was improved highly after theactivated carbon treated by supercritical methanol, which could inhibitthe double bond shift.In conclusion, it is clear that assembled Pt/C, Pd/C catalysts exhibitgood catalytic properties on selective hydrogenation of cinnamylaldehyde and tetrahydrophthalic anhydride. The assemble catalysts wouldhave broad prospect thanks to the advantages such as proceduresimplification, easy to operation and controllability.