Study On The Catalysts For 1,4-butynediol Selective Hydrogenation

1,4-Butynediol and its hydrogenation products include the selective semi-hydrogenated product—1,4-butenediol and the fully hydrogenated product—1,4-butanediol(referred as butanediol or BDO)are all industrial raw materials with high value and wide application.The catalytic hydrogenation of 1,4-butynediol is a complex series of parallel reactions.It has been a research hotspot and an important industrial process.The semi-hydrogenation and full hydrogenation catalysts involved in the process are the key to controlling the selectivity of the reaction products.Therefore,structure design and the preparation of a highly active and highly selective catalyst bring much attention of research,and also the basis for later application.In the first part of this thesis,the catalyst for the selective hydrogenation of 1,4-butynediol to 1,4-butenediol was studied.The bimetallic catalysts of different configurations prepared by chemical reduction method and the conventional impregnation method have significant differences in reactivity and selectivity.The experimental data and characterization results of four catalysts with different structures showed that the presence of PdO species in large quantities will make the activity of the catalyst extremely low,even without activity,while the presence of a large number of NiO species will increase the reaction rate and increase the hydrogenation depth of butenediol.Due to the change of the metal electron state,the state of the bimetallic alloy changes the adsorption strength of the substrate and the product,and also leads to a decrease in the selectivity of the butenediol.Using the macroporous low surface area a-alumina as the support,nickel chloride hexahydrate as the nickel source,and hydrazine hydrate as the reducing agent,the bimetallic catalyst of the Pd/Ni/NiO/a-Al2O3 structure was synthesized and reduced.The 1%Pdl%Ni/?-Al2O3(CR)exhibits high activity and high selectivity under ambient temperature and pressure.The catalyst has a very low precious metal loading,and at mild reaction,but achieving a selectivity of 100%butenediol,and it remains unchanged until the conversion reaches 84%.The relationship between the structure of Pd/Ni/NiO/?-Al2O3 and the hydrogenation of butynediol was investigated by XRD,BET,H2-TPR,H2-TPD,TEM and HRTEM,and the possible reaction mechanism of 1%Pdl%Ni/?-Al2O3(CR)catalyst was prpopsed.In the selective catalytic hydrogenation of butynediol,there is synergistic effect between Pd/Ni/NiO species,Pd metal can activate hydrogen at low temperature,and NiO species can easily adsorb and activate ?-electron-rich butynediol.At the same time,it is beneficial to adsorb more hydrogen.The presence of Ni metal state plays an important role,and it is likely to act as a bridge to transfer hydrogen from the proton to the activated substrate for hydrogenation.In addition,the catalyst almost maintain the structural properties of macroporous and low specific surface area,which makes the product easier to desorption and prevent further deep hydrogenation,thereby increasing the selectivity of the target product butenediol B2D.The second part of this paper is the study of the catalysts for the complete hydrogenation of 1,4-butynediol to 1,4-butanediol.The carbon nanotubes were used as support of the bimetallic PdNi catalyst by stepwise impregnation.Experiments show that the synergistic effect of PdNi bimetals plays a key role.From a kinetics point of view,carbon nanotube support possess excellent hydrogen storage properties,which greatly increase the reaction rate of CNTs-supported single metal or bimetallic catalysts.This kinetically favors the complete hydrogenation product,the butanediol BDO.Secondly,there is a metal bond or electron transfer between the Pd-Ni bimetals,which enhances the adsorption of substrates and intermediates,which is beneficial to further hydrogenation.When the reaction pressure is 2 atm,butynediol reaches 100%conversion in 1 h,and eventually reaches 98.9%conversion.When the pressure dropped to 1 atmosphere,the reactivity did not decrease but the selectivity decreased to 78%.This shows that pressure has a great influence on the selectivity of butanediol,but the mechanism remain illusive.With the increase of Ni content in the bimetal,the dispersion of active Pd in the catalyst is more uniform,and the electronic state of Pd and Ni also changes further.The selectivity of BDO in butanediol also gradually increases.