The selective hydrogenation of carbonyl groups of the conjugated carbonyl compounds is an important reaction in the pharmaceutical and chemical industries,and several selective hydrogenation approaches have been developed.Using stoichiometric hydrides (LiAlH₄,NaBH₄,etc.) as hydrogenation reagents has some shortcomings,including the unsatisfied selectivity of target product owing to the simultaneous hydrogenation of conjugated double bonds and carbonyl groups,as well as the flammability and explosibility of hydrides.Hydrogen is an alternative hydrogenation reagent,which can selectively hydrogenate carbonyl groups by homogeneous and heterogeneous catalytic processes.The noble metal (Ru,Pd,etc.) complexes were usually used in the homogeneous catalytic process,which caused some serious issues such as the metal residues in products and the difficulties of recovering precious catalysts.These problems can be effectively solved by the heterogeneous catalytic process using the supported catalysts.Carbon-based materials,metal oxides and β-Zeolite are commonly used supports.Among them,carbon-based materials are preferable due to their features of abundant morphologies and structures,good stability,adjustable specific surface areas and pore structures,easy doping,etc.Interestingly,the introduction of heteroatoms into carbon matrix can provide a plenty of anchoring sites to disperse catalytically active species and regulate the interaction between active species and support,and hence promotes their catalytic properties.In addition,the high specific surface areas of the supports are beneficial to the dispersion of the catalytically active species.In recent years,our group has developed hierarchical carbon-based nanocages by in situ MgO template method.The mesostructured nanocages feature the high specific surface area,coexisting micro-meso-macropore structure,rich defects,easy doping,etc.,which demonstrated excellent electrochemical performance in energy conversion and storage.Herein,taking advantage of the anchoring functions of nitrogen heteroatoms and high specific surface area of nitrogen-doped carbon nanocage (hNCNC),10 wt% Ru/hNCNC catalyst was conveniently prepared by microwave-assisted ethylene glycol reduction.The Ru nanoparticles of ca.2.4 nm are highly dispersed on the outer surface of hNCNC.As the catalyst for the selective hydrogenation of acetophenone to 1-phenylethanol,Ru/hNCNC exhibits excellent catalytic activity,selectivity and recyclability in mild conditions of 50.0℃ and 2.0 MPa H₂.Specifically,after 2.0 h of reaction,the conversion of acetophenone is up to 96.2%,obviously higher than that of Ru/carbon nanocages (Ru/hCNC,80%) and Ru/AC (0.7%),and the selectivity of 1-phenylethanol is 95.8%.More importantly,after recycle use for 6 times,the conversion of acetophenone only slightly drops from 96.2% to 94.0% for Ru/hNCNC,while obviously decreases from 80.0% to 63.0% for Ru/hCNC.Such excellent catalytic performance of Ru/hNCNC could be ascribed to the synergism of (i) the high dispersion of Ru nanoparticles owing to the high specific surface area and nitrogen doping of hNCNC,(ii) the regulated electron structure of Ru catalyst owing to nitrogen incorporation,iii) the facilitated mass transportation by unique hierarchical pore structures of hNCNC support.

Key words: acetophenone, selective hydrogenation, 1-phenylethanol, nitrogen-doped carbon nanocages, ruthenium