| Acetone and ethanol are increasingly important biomass platform molecules,and there are high value-added chemical products or intermediates such as isoferlone and n-butanol in their downstream respectively.Therefore,it is of great practical and theoretical significance to transform these biomass platform molecules into high value-added organic matter with long carbon chain through coupling reaction using heterogeneous catalytic process.On the other hand,in the theoretical development of cooperative catalysis,how to combine and match multiple sites involved and the analysis of the role of cooperative catalysis are important issues in this discipline.In-depth analysis of these problems will greatly enrich the theoretical connotation of cooperative catalysis and improve the theoretical guidance for the development of new cooperative systems.In this study,solid acid-base and its synergistic effect catalyzed the conversion of biomass platform molecules.In the process of research,the author has realized the policy of"two hands":emphasizing the development of high efficiency,low cost and industrial oriented catalysts,and also devoting to explaining the catalytic mechanism and the relationship between"structure and catalytic behavior".Specifically,this study combined experimental and theoretical calculations to explore the effects of complex micro and nano structures of catalysts（including heteroatomic doping,double site intimacy,and plane effects）on catalytic performance,and extracted the"structure-activity"relationship between the structure of the active site and catalytic behavior.The contribution of this paper is mainly in the following aspects:First,we report an acid-base catalyst with outstanding performance for acetone condensation and ethanol coupling.Secondly,the principle of acid-base co-catalysis and its dependence on the intimacy of two-site were clarified,and the chemical essence of co-catalysis was clarified in the two steps of dehydrogenation and coupling,which enriched the connotation of dual-site co-catalysis.Thirdly,the interface construction strategy of zeolite@oxides and the research method of"structure-effect"relationship proposed in this paper are of popularization significance and provide ideas for the research of similar catalytic systems.In the first part of this paper,the synthesis and catalytic properties of a single solid acid or base were investigated,and the relationship between the"structure-property-catalytic behavior"of the surface of these acids and bases was clarified.A variety of composite oxides of different proportions were synthesized and their catalytic properties were investigated.The results show that the solid bases of Mg-Al-Zr series are all cubic magnesite phase.The condensation property of acetone was determined by the properties of solid base.DFT calculation and characterization showed that the introduction of Al atoms could induce lattice distortion,so that the plane site of the cubic magnesite shows the property of high-energy corner,thus increasing the adsorption sites of acidic molecules and increasing the adsorption energy.Acidic zeolites have also been employed to catalyze acetone conversion,whose intrinsic activity is weaker than that of solid base.In situ spectroscopy and intermediate experiments confirmed that the formation of mesitylene catalyzed by solid acid did not come from the isomerization of isophorone.In the second part of this paper,the structure-activity relationship of"crystal surface effect-catalytic performance"on CeO2 surface of classical acid-base synergistic catalyst was explored,and CeO2 catalysts with different advantageous crystal surfaces were synthesized under control.Probe molecules-TPD,Raman spectroscopy,XPS were used to evaluate the surface properties of the catalyst.For catalytic acetone condensation reaction,the nanorods with（110）crystal morphology of CeO2 have the highest normalized surface activity.The structure-activity relationship of acetone condensation catalyzed by different crystal surfaces was explained by the theoretical calculation results of adsorption energy and live dissociation energy,kinetic experiment and in situ shielding experiment.In the third part of this paper,a co-catalyst rich in adjacent acid-base sites was constructed to catalyze acetone condensation,and the relationship between acid-base co-catalysis mechanism and"dual-site intimacy-performance"was discussed.With the support of DFT differential charge density calculation,this chapter proposes the"ion pair mechanism"to accelerate acetone condensation reaction:activate acetone to form carbocation by acid site,activate the second molecule acetone to form carbocation by base site,and accelerate the carbon-carbon coupling step by charge effect.Accordingly,a generalized catalyst preparation strategy,namely the synthesis of zeolite@oxides,was proposed in this study.Electron microscopy,XPS,CO2-NH3 co-adsorption-desorption and phenol-adsorption desorption were used to characterize the adjacent acid-base sites at the contact interface of the two species.The number of adjacent acid-base sites（intimacy）was controlled by adjusting the milling time of acid components.In the evaluation of acetone condensation performance,it was found that the improvement of the intimacy of the two sites was conducive to the formation of isophorone.Kinetic studies confirm the rationality of the ion pair mechanism.The optimal catalyst demonstrated excellent catalytic performance(1020 mg gcat-1 h-1isophorone yield)and superior catalytic stability（stable operation over 1500 h）.The source of strong carbon resistance can be attributed to the utilization efficiency of base sites under the cooperative catalysis mechanism.In the fourth part of this paper,cooperative interface construction strategy was used to prepare high-performance ethanol coupling catalyst for n-butanol preparation,which showed first-class catalytic performance(n-butanol selectivity greater than 82%,ethanol conversion rate 0.62 h-1).Co-feed kinetics and in situ spectral characterization confirmed that the optimal catalyst surface reaction followed the Guerbet path.The adsorption energy of the two substrates at the acid and base sites explained the competitive adsorption behavior of ethanol and acetaldehyde at the active sites.The normalized activity calculation in the kinetic interval shows that the normalized condensation rate and dehydrogenation rate of the two-site cocatalyst with higher intimacy are more than 3 times that of the physical mixed catalyst.In situ shielding experiments and apparent activation energy calculations also strongly confirmed that the synergistic catalysis of the two sites accelerates two kinetically related steps of dehydrogenation and condensation,and for the first time elucidates the strong activation of C-H bonds by adjacent acid-base sites.When the intimacy of the two components in the catalyst changed,the isotope labeling experiment and KIE experiment obtained completely different results,which clarified that the chemical essence behind acid-base synergistic efficient dehydrogenation was the transition from"ethoxide dehydrogenation mechanism"to the more advantageous"enolate dehydrogenation mechanism".To sum up,the relationship between the"structure-property-catalytic behavior"of solid acid and base surfaces was first clarified in this study.Then,by the strategy of constructing adjacent double sites,the industrial prospect of acetone condensation and ethanol coupling catalyst was prepared.The structure-activity relationship between the intimacy and catalytic behavior was determined by regulating the intimacy of two components in the two-site catalyst.The crystal plane effect in catalytic coupling reaction of CeO2 was analyzed by controlled synthesis.The above work not only provides useful reference for the design of highly efficient coupling catalyst,but also contributes to the improvement of the basic theory of heterogeneous catalysis. |
