Synthesis of Cu_xO-MO_y Binary Catalysts and Its Ethynylation Performance

Author:Wang Zhi Peng

Supervisor:zhao yong xiang


Degree Year:2019





1,4-Butynediol(BD in abbreviation)is an important alkynol organic compound,which has both electron-rich-C≡C-and strongly polar-OH.It has active reaction properties and is extremely versatile.A series of high value-added chemicals and polymer materials can be prepared by using1,4-butynediol as a raw material,whose application fields involve all aspects of national economy and people’s livelihood.1,4-butynediol is synthesized by catalytic conversion,taking the coal-based primary chemical formaldehyde and acetylene as raw materials.As a bridge between coal primary chemicals and downstream high value-added chemicals,it plays a connecting role.And in the high value utilization of coal resources,1,4-butynediol also occupies a pivotal position.The copper-based ethynylation catalyst is the core technology in ethynylation of formaldehyde.From the perspective of technology development,many researchers have carried out research on the preparation conditions of supported CuO-based catalysts,Nano catalysts and malachite,etc.But until now,there is still a lack of research on the structure-activity relationship between the structure and properties of copper-based ethynylation catalysts,and the formation mechanism of the active phase.In this thesis,through constructing the CuxO-MOy binary modal catalysts system,the author systematically studies the promoters and supports effects of copper-based catalysts over ethynylation of formaldehyde.Combined with the various characterization techniques and the evaluation results of the catalyst,the author deeply studies the influence of the state of CuO,the surface acidity and alkalinity of the catalyst,and the collaboration effect of Cu+-alkalic sites on the formaldehyde ethynylation performance of the catalyst,as well as discusses the intrinsic relationship between the structure and properties of the catalyst,and the mechanism of catalytic conversion.The main research contents and conclusions of this thesis are as follows:1.CuO-SiO2 binary catalysts with different Cu/Si ratios were prepared by co-precipitation method.The author studies the effects of SiO2 on the state of CuO,the conversion of active Cu+ species and the catalytic performance.The results show that the introduction of SiO2 can make the catalyst effectively improve the dispersion of CuO under the condition of maintaining proper surface acidity and basicity to promote efficient in situ conversion of Cu2+ to highly-dispersed ethynylation species of Cu+,and effectively prevent the aggregation of active ethynylation cuprous species to expose more Cu+ sites on the catalyst surface.There is a good linear relationship between the ethynylation activity of the catalyst and the amount of Cu+ exposed on the surface,and this clarifies that the Cu+ species is the main active site in the ethynylation reaction.2.The author prepares binary catalysts with different surface properties by co-precipitation method and respectively combining Al2O3,SiO2 and MgO with large difference in surface acidity and basicity with CuO.Based on this,the author studies the effects of different additives on the structure,texture,surface properties and ethynylation activity of each catalyst.The study shows that similar to the SiO2 role of dispersing copper species,Al2O3 can also increase the dispersion of copper species,but the stronger acidic sites on the surface may cause the polymerization of acetylene during the reaction.And the resulting polyacetylene species covers the surface ethynylation active sites,leading to a decrease in catalyst activity.The introduction of MgO can not only improve the dispersion of copper species,but also improve the surface basicity of the catalyst.The active Cu+ species and the basic site act on C≡C and H of acetylene,respectively,and synergistically activate acetylene,thereby greatly improving the ethynylation activity.Further changing the ratio between Cu and Mg can realize the simultaneous regulation of the number of active cuprous species on the catalyst surface and the number of alkalic sites to construct more collaboration sites.Among them,the BD yield ofCu0.75Mg0.25 catalyst was as high as 72.5% under the conditions of reaction temperature of 90 ℃ and reaction time of 10 h.3.Based on the results of the first two chapters,the author combines SiO2 with MgO to study the effects of the introduction way of magnesium species on the surface properties of CuO/SiO2 catalysts and the interaction between copper species and supports.The study finds that different ways of introducing magnesium species may lead to differences in the state of magnesium species,which further affects the texture and surface properties of the supports.The magnesium species introduced by the impregation method are mainly present in the form of MgO particles,which improves the surface basicity of the catalyst;the magnesium species introduced by the sol-gel method enables the support to have not only highly dispersed MgO microcrystals but also Si-O-Mg structure which is generated from the substitution between SiO2 tetrahedral net and Mg species.The formation of Si-O-Mg structure can increase the interaction between the support and the copper species,which is beneficial to the exposure of the active cuprous species on the surface of the catalyst and the stability of the valence state.The most active cuprous species and basic sites are exposed on the CuO/SiO2-MgO catalyst surface,and the strong interaction between the active species and the support stabilizes the valence state of the copper species,which makes the catalyst show the higher activity and stability.4.Extending the ethynylation catalyst system from CuO to Cu2O,Cu2O/TiO2 catalysts with anatase and rutile titania as supports were prepared liquid reduction-deposition-precipitation method and applied in1,4-butynediol synthesis by formaldehyde ethynylation reaction.The effect of different TiO2 polymorphs on structure and catalytic performance of catalyst was investigated,combining with various characterization techniques.The results showed that the ethynylation activity of catalyst with rutile TiO2 as support was obviously higher than that anatase TiO2 as support.This was mainly due to the different surface structures originated from the different crystalline structures of the as-prepared TiO2.The(110)planes are preferentially exposed planes for Rutile TiO2.Compared with anatase TiO2,The higher density vacant sites and different coordination structures of copper species on rutile(110)planes facilitated the formation of more Cu-O-Ti structures,exhibiting stronger interaction between Cu2O and the support.Meanwhile,the stronger interaction between Cu2O and rutile efficiently retained the dispersion of active species and stablized the valence of Cu+,leading to a higher catalytic performance.