Study On The Regulation Of Electronic Structure Of Pd Based Catalysts And Their Catalytic Performance For Hydrogenation

Among them,hydrogenation reaction is one of the widely examined subject for its application from fine chemicals to pharmaceutical manufacturing,and even energy environment(conversion of carbon dioxide and nitrogen oxides),involving all aspects of human life.The key step during the hydrogenation reaction is the difficulty of H2 dissociation.According to literature reports,noble metal catalysts benefit the H2 dissociation,while their industrialization is restricted for their high cost as precious metals.Therefore,how to improve their catalytic efficiency becomes an urgent demand for the current catalytic industry.Compared with other platinum group metals(Ru:4d75s1、Rh:4d85s1、Os:5d66s2、Ir:5d76s2and Pt:5d96s1),Pd has an electronic configuration of 4d105s0.This structure enables the d orbital electrons to jump to the s orbital when receiving external energy.At the same time,the s orbital can provide an empty orbital and form chemical bond with other elements.Due to the unique electronic configuration of Pd,it is endowed with active d-orbital electrons,which makes palladium active sites exhibit excellent catalytic effects in various catalytic reactions.Based on above comments,this paper proposes a synergetic strategy to improve the catalytic activity of Pd based catalysts during hydrogenation reaction through adjusting the ratio of Pd2+/Pd0 on the catalyst,varying the pretreatment conditions,forming alloy structure with another metal or supports substitution.For the project one,multi-organic compounds with functional groups,such as-C=C,-C=O,-N=O and benzene ring,are selectively hydrogenated into alkyl or amido under near ambient conditions over designed Pd based catalyst,which utilizes the synergetic effect between Pd2+species and Pd0 nano-particles during hydrogenation process.During the catalysts preparation,the optimum ratio of Pd2+and Pd0 is obtained through precisely controlling of hydrogen pretreatment duration.The NPC-[Pd](H2-1 5min)catalyst performs superior catalytic efficiency,good selectivity and good functional group compatibility under mild reaction conditions,which is better than homogeneous Pd catalyst(Pd(TFA)2/Bipyridine)and Pd/C samples.This project provides a new synthesis strategy to improve the hydrogenation efficiency of Pd based catalyst.For project two,a NOx recycle route is proposed based on the selective hydrogenation of nitrite to ammonia(NH3/NH4OH)reaction over Pd based catalyst.The DFT calculation of nitrite hydrogenation is initially carried out to estimate the determination steps of N2 or ammonia generation and further guide the catalyst design and preparation.The DFT calculation results indicate that ammonia is more easily generated at the Pd2+ site,and designing catalysts with Pd2+single atoms and Pd nanoparticles will inhibit N2 generation and improve ammonia selectivity.In the experiment,we chose the covalent triazine framework(CTF)as the catalyst carrier and synthesized the catalyst Pd2+/0/CTF according to the theoretically calculated structure,and Pd2+/0/C3N4,Pd2+/0/SiO2,Pd2+/CTF(O2 pretreatment)and Pd0/CTF(H2 pretreatment)are also synthesized as control catalysts.The activity tests reveal that Pd2+/0/CTF sample achieves 100%selectivity to ammonia generation compared with other samples.In addition,the bench tests also prove that 70%NOx could be eliminated and converted into ammonia completely through single cycle under ambient conditions.This project realizes a superior hydrogenation efficiency from NOx into ammonia through the substitution of catalyst support and optimization of Pd0/Pd2+ratios.For the project three,Au is introduced into Pd based catalyst as structure promotor and used to manipulate the electron property of Pd nano-particles.The optimized Pd-Au/AC-NH2 catalyst presents excellent catalytic efficiency in presence of formic acid as hydrogen source.Employing organic hydrogen donor as reactants could enhance the catalytic reaction rates and conversions for catalytic transfer hydrogenation(CTH)process,including alcohols,olefins,ammonia,formic acid and et al.Formic acid is a promising hydrogen donor due to its low toxicity,good stability and cheap price.In this study,we use formic acid as the hydrogen donor to convert a series of hydrogenation reactions under ambient conditions and study the role of formic acid on hydrogenation rationale.This study supplies an efficient pathway to improve the catalytic performance over Pd-Au/AC-NH2 catalyst,also proves the feasibility of formic acid as hydrogen donor.For the project four,we further study the synthesis of formic acid in a green and highefficiency way,which could be treated as the extended examination of project three.Herein,carbon dioxide is captured at room temperature by amino acid aqueous solution,and formic acid is produced through hydrogenation reaction over Pd/C catalyst.After the screening of various amino acids,it is found that L-arginine(L-arg)presents superior storage ability of CO2 and selected as trapping agent and the reaction solution.In details,the TOF of formic acid could achieve 50.4 h-1 after 6 hrs reaction under 1 atm H2 and 0.5 M L-arg aqueous solution as CO2 trapping agent.This work provides an environmentally friendly and green pathway for formic acid generation,meanwhile,the impact of electron property and charge of Pd species over Pd/C catalysts on CO2 hydrogenation efficiency is examined and summarized.