Preparation And Properties Of Heterogeneous Catalysts For Hydrogen Transfer Reactions

Hydrogenation is one of the most fundamental transformations in organic synthesis,and its industrial applications span from fine chemicals to pharmaceuticals synthesis.Compared with direct hydrogenation involving a pressure of H₂,transfer hydrogenation can avoid the handling of autoclaves and hydrogen,and is much safer and easier to handle and thus would represent a green,safe,and economical protocol,which is a rapidly growing field in the context of the high demand for the development of sustainable and green chemistry including economy consideration.To date,plenty of catalysts,ligands,solvents,and hydrogen sources have been explored in the transfer hydrogenation.Although remarkable progress in transfer hydrogenation has been made,it remains difficulties in constructing and developing novel catalytic system that is sufficiently active and environmentally benign for transfer hydrogenation.In this work,our research focused on the design and synthesis of several kinds of typical heterogeneous catalyst for the transfer hydrogenation.The main conclusions are described as follows:1.Pd/g-C₃N₄ catalyst promoted transfer hydrogenation in the efficient synthesis of amine compounds.We report that g-C₃N₄ nanosheets as support materials can significantly boost the efficiency of Pd nanoparticles for the reduction of nitro compounds to primary amines.Using formic acid as hydrogen donor and water as solvent,the optimized 5 wt%Pd/g-C₃N₄ catalyst exhibited an unprecedented performance in the conversion of nitrobenzene to aniline(achieving almost full conversion with an extremely high turnover frequency of 4770 h^-1 at room temperature),showing the best activity e ver reported for heterogeneously catalyzing nitro compounds reduction.Pd/g-C₃N₄ catalyst was also active for the one-pot reductive amination of carbonyl compounds with nitro compounds to obtain the corresponding secondary amines with excellent selectivity?>90%?.Furthermore,Pd/g-C₃N₄ catalyst was highly stable with a wide scope in the synthesis of various amine compounds.2.Copper�nickel alloys catalyzed reduction of aromatic nitro-compounds.We report a facile method for the synthesis of Cu_1-x-x Ni_x alloys with tunable compositions using the thermal decomposition of metal oxalate precursors.In the obtained Cu_1-x-x Ni_x alloys forming solid-solution structure without significant segregation.By varying the molar ratios of copper to nickel,Cu_0.7Ni_0.3 alloy is found to exhibit an optimum catalytic performance toward the reduction of aromatic nitro-compounds to aromatic amino-compounds using sodium borohydride as hydrogen donor.The catalytic activity of the as-prepared alloys depends strongly on the molar ratio s and the strong interaction between Cu and N i.Cu_1-xNi_x alloys also show good magnetic recyclability.Finally,the magnetic properties were also studied to correlate to the catalytic activity.3.Crystalline/amorphous Al/Al₂O₃ core/shell nanospheres as efficient catalysts for selective transfer hydrogenation of?,?-unsaturated aldehydes.We synthesize Al/Al₂O₃ core/shell nanospheres through an electrical explosion of an aluminium wire,which has a unique composite structure with a crystalline Al core surrounded by an amorphous Al₂O₃ surface layer?3.2�0.5 nm thickness?.The as-obtained sample is efficient for selective hydrogenation of?,?-unsaturated aldehydes to corresponding unsaturated alcohols,and shows a high stability under the reaction conditions.The selectivities toward unsaturated alcohols are all higher than 99%at full conversion.The synergistic effect between metallic Al core with a high electrical conductivity and ultrathin amorphous Al₂O₃ shell with abundant unsaturated sites plays an important role in promoting the catalytic activity for selective hydrogenation of?,?-unsaturated aldehydes.4.N-doped carbon materials as efficient catalyst for aromatic nitro-compounds reduction.We directly synthesized N-doped carbon nanosheets material via the facile pyrolysis of chitosan and melamine without the requirement of any catalyst or post-treatment,where C and N resources could be transformed into highly graphitic N-doped carbon.The graphitization degree and the nitrogen content of the materials can regulated by changing the temperature.The presence of electron-rich nitrogen modifies the surface structure of carbons,providing enhanced electron transfer ability and changeable surface adsorption energy,which enables the applications of carbon with improved performance in catalysis.Under aqueous conditions with hydrazine hydrate as a hydrogen donor,CN-800?pyrolyzed at 800 ^oC?as non-metallic solid catalysts exhibited an optimum catalytic performance toward the reduction of nitrobenzene to aniline,but also can be reused for more than 5 times.