Preparation And Catalytic Properties Of Pdrhp Amorphous And Pdcu Crystalline Alloy Nanoparticles

Precious metal palladium is the main active component for the hydrogenation catalytic reactions in petrochemical field. Recently, studies on the partial hydrogenation of triple carbon-carbon bonds over Pd-based catalysts have drawn great attentions. However, the selectivity of pure palladium catalysts is very low because of the possible formation of hydride phase on the active site. In order to improve the utilization degree of palladium, researches make many efforts on adding a second metal or metalloid to the pristine palladium catalyst. The incorporation of a second metal is an effective approach for tailoring electronic and geometric properties, optimizing the catalytic performance. In this work, we report the synthesis of monodispersed PdRhP amorphous and PdCu crystalline alloy. The catalytic performances of these two catalysts are investigated in the chemoselective hydrogenation of various alkynes. The results obtained are presented as follows.(1) In this work, palladium-rhodium-phosphorus amorphous alloy nanoparticles were prepared via a facile one-pot liquid phase reduction method, by using trioctylphosphine as the stabilizer and oleylamine as the reductant. TEM images show the nanoprticles disperse uniformly with particle size of5nm. The amorphous structure was confirmed through the XRD, HRTEM, SAED technique. Trioctylphosphine imposes an important effect on the formation of amorphous structure. The amorphous structure disappears and divides to Pd and Rh2P crystal phase after high temperature calcination, suggesting that the introduction of P leads to the formation of amorphous naoparticles. The aberration-corrected scanning transmission electron microscopy with energy dispersive X-ray mapping- scan (STEM-EDS) further demonstrates the uniform distribution of Pd, Rh and P element in each amorphous particle. ICP results show that the as-synthesized amorphous nanoparticles can be denoted as Pd34Rh39P27. The amorphous alloy was used for the selective hydrogenation of various alkynes under rather mild conditions (35℃, atmosphere pressure), employing the pristine Pd, Rh, Pd/C and Rh/C as contrast catalysts. Both a high activity and selectivity were obtained for the PdRhP amorphous catalyst, accompanied with satisfactory stability and recyclability, which is significantly superior to their single counterparts. The introduction of lowly-active Rh and P into the highly-active Pd so as to tune the geometry of active site and electronic state of surface atoms, would facilitate the adsorption behavior of reactants and the enhancement of selectivity.(2) We synthesized monodispersed crystalline PdCu alloy nanoparticles (NPs) via co-reduction of Pd(acac)2and Cu(acac)2, employing trioctylphosphine (TOP) as the stabilizer. TEM images show that the as-synthesized nanoparticles are spherical morphology with particle size of8-12nm. XRD patterns suggest that the as-synthesized nanoparticles correspond to PdCu(1:3), PdCu(3:1) and PdCu crystal phase, respectively. The compositions of nanoparticles were confirmed by ICP technique. The catalytic performances of these alloy catalysts were investigated in the chemoselective hydrogenation of phenylacetylene. The PdCu(1:3) alloy shows the worst catalytic performance with low catalytic activity. In contrast, The PdCu(3:1) catalyst displays the highest catalytic activity, selectivity (95%) as well as excellent stability. The addition of non-precious Cu element improves the utilization rate of active palladium and significantly enhances the resulting catalytic performance.