Adjusting Palladium Catalyst To Realize High Selectivity Of 2-Phenylpiperidine

2-Phenylpiperidine is an important intermediate for drug synthesis.Among them,the selective hydrogenation of 2-phenylpyridine is one of the most effective ways to obtain 2-phenylpyridine piperidine.However,the hydrogenation reaction conditions of 2-phenylpyridine are more severe,and the target product selectivity of the catalyst and the conversion rate of the substrate are generally lower.This is mainly because 2-phenylpiperidine is strongly adsorbed on the catalyst and is not easily desorbed,overhydrogenation occurs,and 2-phenylpiperidine has low selectivity.This paper aims to adjust the electronic structure of Pd by adjusting the particle size and doping of non-metallic elements,so as to achieve the high selectivity of 2-phenylpiperidine in the selective hydrogenation of 2-phenylpyridine.(1)In this paper,titanium tetrachloride is used as the titanium source,urea is used as the nitrogen source,and low-order phenolic resin is used as the carbon source.Two-dimensional hexagonal TiO2/C-N is synthesized by solvent evaporation induced self-assembly(EISA).PdC12 is a source of palladium.By adjusting the amount of PdC12 added,a Pd/TiO2/C-N catalyst with controllable particle size was obtained.The specific surface area of the catalyst is about 290 m2/g,the pore volume of BJH is about 0.21 m3/g,and the pore size is about 3.8 nm.Pd nanoparticles(NPs)are evenly dispersed in the pores of the carrier,with a size of 0.5 nm-7.0 nm.The coordination between the nitrogen species and the metal and the restriction of the pore wall effectively limit the transfer and agglomeration of palladium nanoparticles.Combined with XPS and other characterizations,it was found that the size of Pd nanoparticles and the molar ratio of N and Pd significantly affect the binding energy position of Pd,and the effective regulation of Pd electronic structure was realized.(2)To explore the catalytic activity and stability of Pd/TiO2/C-N catalyst for the selective hydrogenation of 2-phenylpyridine.Under the reaction conditions of 90?and 2 MPa H2,the conversion rate of the 2.1 nm Pd/TiO2/C-N catalyst in the selective hydrogenation of 2-phenylpyridine reached>99%under the reaction conditions of 12 h.The selectivity of phenylpiperidine is>99%,and the conversion frequency(TOF)reaches 24 h-1,which is much higher than that of commercial Pd/C catalysts.The result of the catalyst's TOF value increases from small to large as the particle size increases,and then decreases,forming an obvious volcanic curve.The kinetic experiments also proved that the 2.1 nm Pd/TiO2/C-N catalyst has a higher rate constant than other catalysts.It is further proved that the particle size of Pd NPs and the molar ratio of N and Pd change,and the surface electronic structure of Pd also changes,so the adsorption of 2-phenylpyridine also changes,which affects the 2-phenylpyridine Selectivity of hydrogen reaction.Deuterium(D2)proved that the rate control step in the selective hydrogenation of 2-phenylpyridine is the adsorption and dissociation of hydrogen.We used mercapto SH-SBA-15 to capture the lost Pd ions,and no palladium ions were lost in the experiment.Six cycles of 2.1 nm Pd/TiO2/C-N were carried out.The selectivity and conversion of 2-phenylpyridine hydrogenation did not change significantly,which proved that the catalyst was stable and not lost.