| The produce of biofuel is of great significance to optimize the energy structure in China.2,5-Dimethylfuran(DMF),a liquid biofuel that can replace petroleum,is generated from the hydrodeoxygenation(HDO)of 5-hydroxymethylfurfural(5-HMF).5-HMF consists of various functional groups,such as hydroxymethyl,aldehyde and furan ring.The reaction routes are complex and high selectivity of DMF is challenging.Therefore,it is important to design an efficiency catalyst that exhibits good performance for C=O/C-O hydrogenolysis and poor activity for the furan ring hydrogenation.Supported metal catalysts have many advantages,such as high utilization of active components,easy to separation and good reusability,in line with the demand of green chemical industry,and are widely used in fine chemical industry.In the current study,the properties of the interface,which are affected by metal-support interaction(MSI),exhibit an important effect on the catalytic activity and selectivity.Controlling the support composition is one of the effective ways to affect the interface properties.Mix metal oxides(MMO)is a common material that combines a variety of high-priced non-noble metal components.It has played an important role in many catalytic reactions.The two components enter the lattice of each other,showing a different property from a single oxide,which is expected to form a special interface structure.Therefore,based on characteristics of the compositional tunability and topological transformation of layered double metal hydroxides(LDHs),three MMO materials were prepared as supports to produce Pt based catalysts.First,it was found that the interface structure of the Pt/CoTi-MMO catalyst was superior to the conversion of 5-HMF.So the active cites formed at the catalyst interface and the mechanism of the reaction were studied.Second,the reduction temperature of the Pt/CoTi-MMO can affect the properties of catalyst interface,which has an influence on the adsorption and activation behavior of reactive molecules.Finally,a non-noble metal Ni/CoAl-MMO catalyst was designed,and the effect of metal-acid synergy in the interface structure on the selective conversion of 5-HMF was clarified.The specific research results are as follows:(1)Pt/Co4Ti-MMO-400 catalyst is obtained by using Co4Ti-MMO as the support,which is topotactic transformation from Co4Ti-LDH precursor.In addition,Pt/Mg4Ti-MMO-400 and Pt/Co4Al-MMO-400 were prepared by using the same loading method with titanium-containing Mg4Ti-MMO and cobalt-containing Co4Al-MMO as the support.Studies have shown that the metal-CoTi-MMO interface(Co2+-O-Ti3+_Vo)was formed in the Pt/Co4Ti-MMO-400.Pt/Co4Ti-MMO-400 is high selectivity to DMF(90%)at the condition of 150? and 1.5 MPa H2.PtCo bimetallic particles are more dispersed on the support,with an average size of-5 nm;in addition,the Co2+-O-Ti3+_Vo interface is enriched with Lewis acid sites(Co2+,Ti3+)and oxygen vacancies Vo.The Lewis acid site can effectively enhance the activation ability of the C=O;the activation of the furan ring can promote the cleavage of the C-O,the Vo site is easy to adsorb O in the C-O bond,and the Co2+-O-Ti3+structure can weaken the aromaticity destruction of the furan ring.(2)Changing the pretreatment conditions of the Pt/Co4Ti-MMO precursor,the interface properties of the catalyst were adjusted,and the composition of CO2+/(CO0+Co2++Co3+),Ti3+/Ti4+and oxygen vacancies in this interface was optimized.The study found that with the increase of the reduction temperature(300-500?),the size of the metal particles increased slightly and the amount of surface-active metals decreased,resulting in a gradual decrease in the dissociation capacity for H2 and the amount of overflow hydrogen.With the increase of the reduction temperature,the Co2+/(Co0+Co2++Co3+)at the interface increases first and then decreases,and the ratio of Ti3+/Ti4+ does the same,reflecting that the amount of Co2+-O-Ti3+ first increases and then decreases,but the oxygen vacancy concentration has been gradually decreasing.In the interface of Pt/Co4Ti-MMO-400,Co2+/(Co0+Co2++Co3+)and Ti3+/Ti4+have the highest values,so exhibits the strongest adsorption and activation ability for C=O;on the other hand,the oxygen vacancy can satisfy the need of C-O hydrogenolysis,the highest proportion of Co2+-O-Ti3+ can minimize the destruction of the aromaticity of the furan ring,and inhibit the generation of over-hydrogenation and ring-opening products.At the same time,the hydrogen dissociation capacity of the catalyst is moderate,so it shows the best DMF selectivity.(3)To replace the noble metal,a non-noble metal Ni/CoAl-MMO catalyst was designed and synthesized for 5-HMF selective hydrogenation reaction.Specifically,the active metal Ni is introduced into the Ni5CoAl2-LDH,and is dispersed at the atomic level.During the calcination-reduction process,Ni-based catalyst,active metal Ni supported on CoAI-MMO is topotactic transformation.Due to the strong interaction between the components in the NiCoAl-MMO precursor,NiO is obtained in good dispersion and stability,and this interaction is gradually strengthened with the increase of the calcination temperature.The calcination temperature of the precursor also affects the surface acid properties of the catalyst.Among them,the number of weak acid sites and medium strong acid sites gradually decreases with the increase of the calcination temperature,and then increases slightly,while the strong acid sites are only obvious at low calcinated temperature(450?).Ni/CoAl-MMO-CT-450 has the largest number of acid sites and the highest acid strength,so it has the highest activity for C=O/C-O hydrogenolysis,and obtained the highest total yield of DMF and DMTHF(85.14%).The Ni/CoAl-MMO-CT-700 sample,only 22.43%yield was obtained under the same conditions.Therefore,by adjusting the calcination temperature to change the crystal structure and reducing properties of the metal oxide,the interfacial properties of the catalyst can be affected,thereby affecting the performance of the 5-HMF selective hydrogenation reaction. |
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