Fabrication Of Biomass-derived Porous N-doped Carbon Supported Co-based Nanocatalysts And The Study Of Catalytic Hydrogenation Performance

As the most abundant renewable resource on the earth,biomass has the advantages of wide distribution,huge reserves,low prices and short renewable cycles.From the point of view of economic efficiency and green development,the conversion of renewable biomass and its derivatives into high-value materials,fuels and chemicals using appropriate catalysts is a highly promising route to replace fossil energy.Furfural,as one of the most competitive biomass-based platform compounds,is currently the only industrially produced platform,with an annual production capacity of more than400,000 tons.The synthesis of high value-added chemicals from furfural has been a hot research topic,while two-thirds of the annual furfural is used to produce furfuryl alcohol.Furfuryl alcohol is an important organic chemical raw material,which is widely used in fiber synthesis,furan resin and pesticide synthesis.However,due to the presence of aldehyde groups and furan rings,furfural has very active chemical properties,and it is difficult to control the degree of hydrogenation during the catalytic reaction,which can lead to different chemical reactions to form furfuryl alcohol,tetrahydrofurfuryl alcohol,methyl furan and cyclopentanone.Therefore,it is important to develop an efficient catalyst for the hydrogenation of furfural to produce furfuryl alcohol.Loaded catalysts are often used for the catalytic hydrogenation to produce fine chemicals.Among them,nano-noble metal catalysts generally have high catalytic performance,but high prices and low reserves will inevitably limit their long-term industrial applications.Therefore,the preparation of efficient hydrogenation catalysts using non-noble metals with abundant reserves has received much attention from scientists.In this work,to address the problems of easy agglomeration and low catalytic activity of non-precious metal atoms,nitrogen atom-doped porous carbon materials（NC）was prepared by low-temperature hydrothermal-high-temperature carbonization using natural bamboo shoots as raw material,and successfully prepared small-sized Co₃O₄@NC catalysts using a low-temperature thermal decomposition process of cobalt nitrate.This green and simple preparation method allows Co₃O₄ nanoparticles with an average size of 11.89 nm to be uniformly distributed on the surface of the nitrogen-doped porous carbon material.The material has the advantages of large specific surface area,high nitrogen content,good dispersion in isopropanol and high adsorption of furfural.Due to these properties,the novel cobalt-based nanocatalyst exhibits high activity,selectivity and stability in catalytic furfural hydrogenation reactions.The reaction was carried out at 1 bar H₂ and 160°C for 6 h using isopropyl alcohol as solvent,with a conversion of 98.7%and a selectivity of 97.1%for furfuryl alcohol.The catalysts showed high catalytic activity for the hydrogenation and reduction of a wide range of carbonyl compounds.The excellent catalytic activity of Co₃O₄@NC was mainly due to the synergistic effect of the porous nitrogen-doped carbon material NC with nano-Co₃O₄.Combining the results of characterizations and catalytic reactions,a possible pathway for Co₃O₄@NC-catalyzed hydrogenation of furfural is proposed in this paper.Co₃O₄ nanoparticles can adsorb and activate H atoms in hydrogen.N sites mainly adsorb H⁺in isopropanol,and both hydrogenation and hydrogen transfer hydrogenation pathways exist in the hydrogenation reaction.Based on the previous work,a second metal Cu is introduced into the Co₃O₄@NC catalyst to further improve its catalytic performance by reducing the activation energy through the synergistic effect of the bimetal.The porous Cu@NC material was obtained by the high-temperature pyrolysis of the mixture of copper nitrate and hydrothermal carbon,which can in-situ dope the monatomic Cu into the N-doped carbon material.The Co₃O₄ nanoparticles were loaded onto the Cu@NC by a cobalt nitrate low-temperature pyrolysis process to prepare the Co₃O₄-Cu@NC catalyst.As a result of the conjugate size effect between Cu and Co,the average particle size of Co₃O₄nanoparticles decreased to 7.45 nm due to uniform loading on nitrogen-doped porous carbon surfaces.Compared with Co₃O₄@NC,the bimetallic catalyst still retains the advantages of high nitrogen content and good dispersion in isopropanol,and has a larger specific surface area,which can adsorb more furfural on the surface.Therefore,the Co₃O₄-Cu@NC catalyst showed higher activity in the selective hydrogenation of furfural,and could completely convert furfural at 1 bar H₂ and 160°C for 2 h with isopropanol as solvent.Co₃O₄-Cu@NC catalyst has 1.64 times higher activity than Co₃O₄@NC under the same conditions.The cycling and hot filtration experiments demonstrated that Co₃O₄-Cu@NC has excellent stability and good anti-leaching properties,which can maintain high activity after 5 cycles.Combining the characterization and catalytic reaction results,a possible pathway for the Co₃O₄-Cu@NC-catalyzed furfural hydrogenation reaction was proposed.The hydrogenation process involves both hydrogenation and transfer hydrogenation.The Cu and Co₃O₄nanoparticles can adsorb and activate the H atoms in hydrogen,and the N site generates NH⁺and isopropoxy by adsorption of H⁺dissociation in isopropanol.This work provides new ideas for the utilization of natural biomass and the design of efficient non-noble metal hydrogenation catalysts.