Oxygen Vacancies Promote The Reaction Of Furan Aldehyde Hydrogenation Ring Rearrangement To Cyclopentanone Compounds

Upgrading furan aldehydes（such as furfural or 5-hydroxymethylfurfural）to cyclopentanone compounds（such as cyclopentanone or 3-hydroxymethylcyclop entanone）is of great significance for the synthesis of high-value chemicals and biomass utilization.The development of an effective reducing metal/acid carri er with Lewis acidity is the key to promote the C=O hydrogenation and hydro lysis steps in the hydrogenation ring rearrangement reaction.At present,the Br（?）nsted acid in the reducing metal/acid support will cause carbon loss in the re action,while the weaker Lewis acid is difficult to initiate the hydrolysis step.Therefore,it is very important to design a bifunctional catalyst with high selec tive C=O hydrogenation ability and Lewis acid-catalyzed ring rearrangement ab ility for the synthesis of cyclopentanone motif from furfural derivatives.In order to solve the above problems,a series of recyclable catalysts with single Lewis acidity and abundant oxygen vacancies were designed and prepared in this paper.The main research contents and conclusions are as follows:（1）The pure Lewis acidic pyrochlore supports(La₂Sn₂O₇,Y₂Sn₂O₇ and Y₂(Sn_0.7Ce_0.3)₂O_7-δ)in the form of A₂B₂O₇ were studied,which have the same crystal structure and different metals.The Lewis acidity and surface properties of pyrochlore can be adjusted by inserting different types of A and B metals.After immersion,Pd nanoparticles with appropriate particle size are uniformly loaded on the surface of the pyrochlore.For the reaction of furan aldehyde,all pyrochlore-based catalysts show faster hydrogenation and hydrolysis rates than traditional supported catalysts due to the oxygen vacancies of the support and pure Lewis acidity.Among these pyrochlore-based catalysts,Pd/Y₂Sn₂O₇ has higher activity and selectivity than Pd/La₂Sn₂O₇.Moreover,the Y₂Sn₂O₇-based catalyst partially substituted by Ce³⁺ions at the B site is more effective,and the yields of cyclopentanone and3-hydroxymethylcyclopentanone are the highest at 95.0%and 92.5%,respectively.In addition,the catalyst can still maintain effective activity and stability after 4 runs.（2）A type of pyrochlore compound(2.68wt%Y₂(Sn_0.65Al_0.35)₂O_7-δ/Al₂O₃,7.74wt%Y₂(Sn_0.65Al_0.35)₂O_7-δ/Al₂O₃)was studied.After Pd nanoparticles are impregnated,the oxygen defect of pyrochlore/Al₂O₃ exhibits dual functions:they can adsorb C=O,selectively promote the C=O hydrogenation step,and increase the accessibility of coordinated unsaturated metal ions,thereby providing Lewis acidic sites for the ring rearrangement step.The composite-based catalysts show significantly higher hydrogenation and hydrolysis rates than their corresponding single metal oxide-based catalysts（Pd/Al₂O₃,Pd/Y₂Sn₂O₇）.Finally,the cyclopentanone yield of 7.74wt%Y₂(Sn_0.65Al_0.35)₂O_7-δ/Al₂O₃ was 98.1%,and the yield of 3-hydroxymethylcyclopentanone was 90.6%.ATR-IR verified the catalytic mechanism and emphasized the importance of oxygen vacancies.（3）A series of La₂B₂O₇（B=Ti,Zr,Ce）metal oxides are studied,which are characterized by the same chemical formula but different topological structures.After loading Pd,Lewis acidity and metal-support interaction are dominated by the type of support,which further affects the hydrogenation and acid catalytic ability.More than82%of cyclopentanone was obtained through the hydrogenation ring rearrangement route on Pd/La₂Ti₂O₇.However,Pd/La₂Ce₂O₇ shows very high catalytic efficiency for tetrahydrofuranol,and the yield through the complete hydrogenation route is about 80%.In addition,the catalyst exhibits excellent recycling performance and structural stability.This study proposes an interesting design strategy to selectively prepare cyclopentanone and tetrahydrofuranol by adjusting the adsorption mechanism.