Perovskite LaFeO₃ Prepared By An In Situ Produced Carbon Method For Catalytic Transfer Hydrogenation Reactions

Perovskite oxides with excellent hydrothermal stability are usually applied to the catalytic redox reaction and seldom used in catalytic acid-base reaction.Nanoporous perovskite oxides with high surface area and more active sites facilitate the contact of reactant and catalyst giving rise to the improved catalytic performance.A simple,low cost and environment-friendly method for nanoporous perovskite is urgently needed because of the limitation of template methods.In this paper,nanoporous La Fe O₃ and the composites of La Fe O₃ and carbon were synthesized by in-situ template method and applied to catalytic transfer hydrogenation of furfural.The relationship between physicochemical property and catalytic performance was investigated.Nanoporous perovskite La Fe O₃ was prepared by in-situ produced carbon template method and the specific surface area was higher than that of La Fe O₃ by traditional sol-gel method.The physicochemical properties of porous La Fe O₃ were characterized by XPS,CO₂-TPD and NH₃-TPD measurements which are distinct from La Fe O₃ by sol-gel method.A La-enriched composition,abundant oxygen vacancies and strong acidity-basicity were found on the surface of porous La Fe O₃.For catalytic transfer hydrogenation of furfural,porous La Fe O₃ exhibited better catalytic activity than La Fe O₃ by sol-gel method and the catalytic stability of porous La Fe O₃ was also investigated.According to the results from experiment and theoretical calculation,a reaction mechanism was proposed for catalytic transfer hydrogenation of furfural over La Fe O₃,where the conversion proceeds following an acid-base mechanism.Carbon materials were filled into the stacked holes of La Fe O₃ nanoparticles by in-situ method to promote the catalytic reaction rate on the active sites.Perovskite La Fe O₃ was coupled with micro-mesoporous carbon which has the adsorption ability for organic compound.The carbon component functions as a mass carrier of reactants leading to the high reaction efficiency of active sites.The carbon of composite is uniformly distributed in La Fe O₃ nanoparticles from TEM images.The surface area of La Fe O₃ and carbon composite?148 m²/g?is much higher than that of La Fe O₃ from the composite by the removal of carbon.The composite of La Fe O₃ and carbon exhibited better catalytic activity and the La Fe O₃ reaction rate of the composite showed an increase of 31%compared with La Fe O₃ by removal of carbon.The adsorption ability of carbon for reactants was confirmed by vapor pulse adsorption and the carbon of composite played an important role in high catalytic efficiency due to the adsorption and transferring of reactant to active sites.The perovskite La Fe O₃-carbon composites were prepared from different carbon source?glucose,sucrose,soluble starch,fructose and maltose?.The effect of carbon sources on the physicochemical properties and catalytic performances was investigated.The various carbon precursors did not influence the formation of perovskite oxides but change the surface ratios and valences of elements as well as the acidity-basicity.Among the as-prepared perovskite and carbon composites,the catalyst from maltose precursor exhibited the highest catalytic transfer hydrogenation acitivity.It is due to the La enrichment and strong basicity on the surface of the composites.The test for apparent activation energy was conducted and the recycling stability for furfural hydrogenation and the activities for other carbonyl compounds were also investigated.To provide more insights into physicochemical property of La Fe O₃,A or B site doped La_0.95A_0.05Fe_0.9B_0.1O₃?A=Ca,Ce and Sr;B=Mg,Al,Mn and Zr?were prepared by in-situ produced carbon template method.The molar ratio of Fe⁴⁺/Fe³⁺,reducibility and acidity-basicity on the surface were affected by doped ion types on A/B sites.A cooperative action of acid sites(La³⁺and Fe⁴⁺)and basic sites was observed in doped La Fe O₃ for catalytic transfer hydrogenation process.