Influence of Physical Properties of Al2O3 on Catalytic Performance of Ni/Al2O3 Catalyst for Secondary Hydrogenation of Butynediol
|Course||Physical and chemical|
|Keywords||Butane-1,4-diol Secondary hydrogenation Alumina Pore Structure Silicon modified|
Butane-1,4-diol is a basic organic chemical raw with high additional value material and useful intermediate in the manufacture of fine chemicals. The secondary hydrogenation of 2-butyne-1,4-diol is a key process widely applied in the production of butane-1,4-diol by Reppe method,which is a complex system composed of consecutive parallel reactions.The main aim of secondary hydrogenation is transformation of 2-butene-1,4-diol,the formation ofγ-hydroxybutyraldehyde and acetal from 2-butene-1,4-diol to butane-1,4-diol through catalytic hydrogenation.Eessence of the second step reaction is hydrogenation of "C=C" and "C=O".Pore structure and surface acidity property of Ni/γ-Al2O3 catalyst determined by properties of support have important influence on activity,selectivity and stability of catalysts.Obviously,it is particularly important to select support with suitable pore structure and surface acidity property.Based on the background of "the national 863 project" "the core technology of catalytic hydrogenation of 2-butene-1,4-diol to butane-1,4-diol—localization research and development of secondary hydrogenation catalyst",effect of pore structure and surface acidity property ofγ-Al2O3 on structure and catalytic activity of Ni/γ-Al2O3 catalyst was deeply discussed from basic research aspect.In this paper,alumina with different pore structure was prepared by kneading method with activated carbon,ammonium carbonate,polyvinyl alcohol and polyethylene glycol as pore-expanding agent.SiO2-modified alumina was prepared by kneading method with tetraethyl orthosilicate as silicate source.Supported Ni-catalysts were prepared by the incipient wetness impregnation method and characterized by N2 adsorption-desorption,X-ray diffraction（XRD）, temperature-programmed reduction（TPR）,temperature-programmed desorption of hydrogen（H2-TPD）,temperature-programmed desorption of ammonia（NH3-TPD）,transmission electron microscopy（TEM）,and UV-visible spectroscopy techniques（UV-vis）.Effect of pore structure and silicon modification on the structure,surface property and catalytic performance of Ni/Al2O3 catalyst was investigated.Some regular results were obtained which provide indispensable theoretical basis for localization research and development of secondary hydrogenation catalyst.The results mainly involve the following two parts:The first part is the control of pore structure and effect of pore structure on catalytic performance of Ni/Al2O3 catalyst for secondary hydrogenation of butynediol.In the step of shaping,alumina with an average pore size of 8.0～10 nm was prepared with different pore-expanding agent.Its pore structure belongs to mesopore and specific surface area is above 200 m2/g. Especially,the alumina prepared with activated carbon as pore-expanding agent has high specific surface area and pore volume as well as an appropriate pore size distribution.Compared with commercial Al2O3, self-made Al2O3 has higher specific surface area and pore volume.Ni/Al2O3 catalysts show higher dispersion,more active sites structure and high specific density of active sites on the self-made support.Active sites are preferentially exposed on the surface of catalyst.Meanwhile,it has proper proportion of macroporous and small pores.Therefore,Ni/Al2O3 catalyst shows better activity and stability in secondary hydrogenation of butynediol.The second part is the control of surface acidity and effect of surface acidity on catalytic performance of Ni/Al2O3 catalyst for secondary hydrogenation of butynediol.Effect of the introduction way and silicon content on catalytic performance of Ni/Al2O3 catalyst for secondary hydrogenation of butynediol are investigated.The surface acidity of alumina through Si modification by kneading method increases with the increment of Si content,but Al2O3-SiO2 modified by impregnation method shows weaker acidity than non-modified.Meanwhile,Crystal structure of alumina can be changed owing to the introduction of Si and the existing form of NiO has also changed on surface of Al2O3-SiO2.Modification by kneading method makes metal-support interaction stronger and temperature of reduction higher.Al2O3-SiO2 modified by impregnation method has a weaker interaction with NiO.It is found that the existing form of NiO has changed on surface of catalyst.Amounts of NiO weakly interacted with support increase,thus,the NiO phase is easily reduced to produce metallic Ni.The activity of catalyst with different aluminas as support in the secondary hydrogenation is quite different.Compared with the unmodified,their activities depressed,impregnation＞kneading＞unmodified in order.Effect of Si content on hydrogenation performance of catalyst shows some regularity when Al2O3 was modified by kneading method.If Si content is less than 3wt%,Ni/Al2O3-SiO2 catalyst has the better catalytic performance than Ni/Al2O3 catalyst.However,if Si content is over 3wt%,it has the poorer catalytic performance than Ni/Al2O3 catalyst.