Study On The Fabrication And Performance Of Catalysts For The Dehydrogenation Coupling Of Alcohol Compounds

The development and utilization of biomass energy is one of the important ways to promote global energy transformation and realize climate change goals.As a type of biomass-derived platform molecule,the efficient utilization of alcohol compounds has attracted great attention all over the world.Through C-C or C=N coupling reactions,a series of high-value pharmaceutical and chemical intermediates can be produced from alcohol compounds.Generally,this type of reactions involve multiple tandem steps,such as dehydrogenation and condensation.Therefore,high requirements are placed on the type,quantity,and spatial matching of the catalyst’s active centers.To achieve this tandem reaction,we attempt to develop three construction strategies to enhance the catalytic performance of catalysts in dehydrogenation coupling of ethanol and oxidative dehydrogenation coupling of alcohols and amines.The impact of catalyst structure on reaction performance has been studied in detail through various characterization methods and theoretical calculations.The main contents and results are as follows:（1）The dehydrogenation coupling of ethanol to produce higher alcohols involves four tandem steps:ethanol dehydrogenation,aldol condensation of acetaldehyde,dehydration of the aldol,and hydrogenation of crotonaldehyde.The conversion efficiency and product selectivity of this tandem reaction depend on the synergistic effect between the metal sites for dehydrogenation and hydrogenation reaction steps and their acid-base oxide sites for the condensation reaction step.In this section,a homologous RuO₂-Ru heterostructure catalyst with low Ru loading was prepared by a facile in-situ carbothermal reduction method.The optimized RuO₂-Ru/C catalyst with0.75wt%Ru content can effectively catalyze the upgrading of ethanol to n-butanol under relatively mild conditions.A series of characterizations and experimental results indicate that Ru⁰ serves as an active center for dehydrogenation/hydrogenation and RuO₂ catalyzes the aldol condensation and dehydration.In addition,by introducing lanthanum oxide,a stable base site,to construct Ru-LaO_x heterostructures,the catalytic performance of ethanol upgrading can be significantly improved.The catalyst with Ru content as low as 0.5wt%could achieve 25.7%of ethanol conversion and 52.3%of n-butanol selectivity.These results demonstrate that for the complex tandem processes,designing active centers as heterostructures and utilizing their synergistic effects can effectively improve the conversion efficiency of dehydrogenation coupling reactions.（2）Taking inspiration from the heterostructure in the previous work and considering the high price of the noble metals,we chose non-noble metal Cu as the metal sites to construct a Cu-LaO_x strong interaction structure（core-shell heterostructure）catalyst.The resulting Cu-LaO_x/C catalyst exhibited exceptional performance in tandem catalytic upgrading of ethanol at 250℃and 2 MPa;ethanol conversion and the C₄-C₈ alcohols selectivity can reach 42.6%and 71.7%,respectively,comparable with the excellent Pd-Ui O-66 catalyst.Moreover,the Cu-LaO_x/C catalyst also exhibited excellent stability in>120 h on-stream evaluation.Based on the literature and experimental results,it is shown that the Cu cores serve as the active center for dehydrogenation/hydrogenation steps and the LaO_x shells catalyze the condensation of the intermediate products.The synergistic effect of the Cu cores and LaO_x shells endow Cu LaO_x/C catalyst with high catalytic activity.In addition,in the viewpoint of catalyst design,this metal-oxide strong interaction structure is constructed through strain-induced strategy,based on the local strain induced by the exchange between different metal atoms,breaking the limitations on redox property of metal oxides in traditional methods.（3）In the first two sections,lanthanum oxide was used as stable base sites to catalyze the aldol condensation process in ethanol dehydrogenation coupling reaction.In this section,we designed the non-variable valence metal La element as the redox-active center through a single-atom strategy.This single atom catalyst is supported on the mesoporous carbon and can be prepared by a simple impregnation method.Extended X-ray absorption fine structure（EXAFS）measurement and density functional theory（DFT）calculations indicate that the single La atom in the catalyst is coordinated by three N atoms and one O atom and that an O₂ molecule adsorbs onto the single La atom upon exposure to open air.EPR,Bader charge and O₂-TPD analysis indicate that the adsorbed molecular oxygen is activated into superoxide radicals.In the synthesis of imines through the oxidative dehydrogenation coupling of alcohols and amines,with air as the source of oxygen,the single La atom catalyst exhibited superior activity and excellent cyclic stability in comparison with traditional transition metal oxides includingγ-Fe₂O₃,Fe₃O₄,Ni O and Co₃O₄.In addition,to gain deeper insights into the rate-determining step,DFT calculations were performed.The results show that there are two possible reaction paths,and the charge difference on the La atom is within 0.15electron,indicating the redox electron transfer is initiated by the spontaneous adjustment of La-N and La-O bonds instead of the valence change of La center.Moreover,similar catalytic performance is also found in a series of lanthanide catalysts（e.g.Nd,Sm,Gd）,which are seldom designed as redox catalysts previously.This work could offer a new approach for the design of redox catalysts based on non-variable valence metals.In summary,this paper focuses on the dehydrogenation coupling reaction of alcohol compounds.Based on the deep understanding of the reaction path and mechanism,efficient conversion of alcohol compounds to higher alcohols and imines was achieved by adjusting the structure of catalytic materials.These works will provide useful reference for the high-value utilization of alcohol compounds.