Study On Hydrogenation/Isomerization Of 1,4-butenediol Over Ni/SiO₂ Catalyst

In this paper,the Ni/SiO₂ is used to catalyze butenediol hydrogenation reaction starting from the exploration of reaction conditions.On the basis of the selection of the optimal reaction conditions,the structure,texture and surface properties of the catalyst are changed by means of catalyst preparation method and carrier type selection.And then the structure-activity relationship between the structure of the catalyst and the performance of BED hydrogenation is explored.After obtaining some structural characteristics of Ni-Si catalysts,we tried to propose the production path of2-hydroxytetrahydrofuran as a by-product during the hydrogenation of BED,and an important method to suppress side reactions and improve the yield of the target product.This work not only deepened the basic scientific understanding of BED hydrogenation reaction,but also provided useful clues to the study of the hydrogenation mechanism of BYD,and provided a theoretical basis for the design and development of highly selective synthesis of BED,BDO and other chemical hydrogenation catalysts.The main research contents are as follows:1.The effects of temperature,hydrogen pressure,p H value,raw material concentration,solvent and other reaction conditions on the hydrogenation performance of BED were compared and researched.It was found that the temperature increase was beneficial to the hydrogenation of BED to BDO and BOL.It is speculated that the hydrogenation reaction is dominant at high temperatures,and the isomerization reaction is suppressed;It is speculated that in the absence of H2,there is no hydrogenation or isomerization of BED,and it is difficult or impossible to occur the isomerization of BED,and it has the highest selectivity of 2-OH-THF under the condition of low pressure H2,indicating that low pressure of H2 is beneficial for the isomerization reaction;Under acidic conditions,it is beneficial for the isomerization of BED,andpromotes the formation of 2-OH-THF.Excessive alkalinity will destroy the pore structure of the catalyst,which will cause the reaction to proceed toward by-products.When alcohols are used as solvents,the conversion and selectivity of the reaction have been significantly improved.2.We choose to add the auxiliary agent citric acid（CA）to modify the catalyst.The introduction of citric acid can effectively improve the dispersion of Ni species on the catalyst surface,which is beneficial to the formation of Ni species with small grains.It is benefical to the hydrogenation activity of BED.At the same time,the introduction of citric acid makes the SiO₂ support easy to form Ni-O-Si structure.While enhancing the acidity,the Ni-H interaction is stronger,which is more conducive to the formation of2-OH-THF;while large-grain Ni has fewer interfaces,and only a hydrogenation center exists,which is beneficial to the production of the main product BDO;enol The conversion of structure and aldehyde and the self-condensation of aldehyde and alcohol cyclization to 2-OH-THF are directly related to the double bond isomerization performance on the catalyst.3.On the basis of the Ni/SiO₂ catalyst system,the introduction of the support SBA-15 and MCM-41 has changed the texture properties of the catalyst,especially the pore structure size of the catalyst is significantly different,and it has caused the acidic properties of the difference on catalyst.Compared with Ni/SiO₂,the exposed metal centers of Ni/SBA-15 are similar,but Ni/SBA-15 shows a certain acidic center after reduction due to the formation of Ni-O-Si bonds.Under the synergistic effect of the acidic Ni2+center,more 2-OH-THF is formed.Since the adsorbed BED is more likely to generate hydrogenated product BDO under the action of rich active H,there is no subsequent reaction to obtain 2-OH-THF.Ni/MCM-41 and Ni/SBA-15 are similar in acidity but the yield of 2-OH-THF is not high,which may be related to the high exposed metal sites and the smaller pore structure in the Ni/MCM-41 catalyst.With the extension of reaction time,the three catalysts began to decrease after the yield of 2-OH-THF reached a maximum,while the yield of BDO was still increasing,indicating that the 2-OH-THFproduced can be further converted to BDO by hydrogenation.Among them,the conversion range of 2-OH-THF from the maximum value to the minimum value on Ni/SBA-15 is the largest,and it is speculated that the2-OH-THF produced is favored to be converted to BDO under acidic conditions.