Study On The Construction Of Non-noble Bimetallic Catalyst And Its Catalytic Performance On Hydrogenation Of Biomass-Derived Compounds

In recent years,with the rapid development of current technology and industry,the consumption of fossil energy will continue increase significantly in the next few decades,and the environmental problems it brings will also become unimaginable.Therefore,the search for sustainable alternatives to fossil resources has become an urgent problem to be solved in the field of energy.Biomass,as a kind of sustainable renewable resource with wide sources,has been widely concerned.A variety of compounds derived from biomass can be used to produce a variety of high value-added chemicals,and also can be used to produce biofuels by hydrodeoxygenation.Taking biomass derivative furfural as an example,since its discovery in the year of 1821 for nearly 200 years,numerous researchers have studied its application.It was initially used as a rosin decolorant,and later applied to the field of synthetic rubber,and then to the field of drug synthesis and flavor synthesis.At present,furfural has been rated as one of the 30 most important chemicals in biomass derivatives by the U.S.Department of energy.For another example,lignin derivatives such as guaiacol and vanillin can be further used in the field of medicine and perfume synthesis as important chemical intermediates because of their functional group modified benzene ring structure.Due to its high carbon content,this kind of biomass derivatives can be hydrodeoxygenated to obtain ideal bio fuel.Therefore,the study on hydrodeoxygenation of lignin derivatives is very popular in recent years.At present,the mature catalysts for the hydrogenation of biomass resources are mainly noble metal catalysts.Although their excellent stability and good performance have made good progress in this field,the limited reserves and high prices have greatly restricted the large-scale industrial application.Hence,the effective substitution of noble metal catalysts has become a hot topic in the field of biomass catalytic conversion.Non-noble metals,such as iron,cobalt,nickel and copper,are considered to be the most suitable substitutes for precious metals due to their high reserves and relative good performance in hydrogenation reactions,have been widely concerned recently.However,the application of non-noble metal catalysts is still hindered by many obstacles.The problems to be solved include the poor dispersion of active components,agglomeration phenomenon in high temperature and poor stability.As a result,the construction of non-noble metal catalysts with high dispersion,high stability and high activity has great potential and value.As a family of two-dimensional layered material,layered double hydroxides(LDHs),with different metal M2+and M3+ cations uniformly distributed and orderly prearranged throughout the layers,have several advantages including low cost,facile preparation,and adjustable structure/compositions.More importantly,by appropriate thermal treatment under different atmospheres,LDHs can be topologically transformed into highly dispersed supported metal catalysts over mixed metal oxides(MMOs).Most of the non-noble metals can be used to synthesize LDHs,so it is very convenient to prepare supported non-noble metal catalysts through LDHs precursor method.Based on the above viewpoints,a series of non-noble bimetallic catalysts with excellent performance were synthesized through LDHs precursor method in this study.By fine tuning the topology transformation parameters,catalysts with different surface characteristics were constructed and applied to the selective hydrogenation of biomass furfural,vanillin and 5-hydroxymethylfurfural.The structure-activity relationship was investigated in detail by means of X-ray absorption spectroscopy,in situ infrared spectroscopy and DFT theoretical calculation.The specific work is as follows:1.The construction of surface modified Ni-Cu bimetallic catalyst and its performance in the furfural hydra-rearrangementFor heterogeneous supported catalysts,commonly,the adsorption of reactant molecules on the catalyst surface can significantly govern their activity and selectivity.In this paper,it was shown that surface modified bimetallic NiCu nanocatalysts derived from ternary Ni-Cu-Al layered double hydroxide precursors exhibited better catalytic activity trends for the hydrogenolysis of biomass-derived carbonyl compounds compared with monometallic Ni or Cu ones.Specifically,bimetallic NiCu nanocatalyst achieved a maximum cyclopentanone yield of～89.5%in the aqueous phase hydrogenation of furfural.Based on a series of structural characterizations,catalytic experimental results and density functional theory calculations,it was emphatically demonstrated that different catalytic behaviors might stem from the difference in the adsorption modes of the carbonyl group on the surfaces of monometallic Ni and bimetallic NiCu nanoparticles.It was deduced that due to the decoration of abundant surface oxygen species on bimetallic NiCu nanoparticles,the remaining exposed metal surface became η1(O)-type adsorption sites for the carbonyl group,different from the dominant η2(C,O)adsorption mode on monometallic Ni nanoparticles with less surface oxygen species.Most importantly,the present bimetallic NiCu nanocatalyst displayed superior catalytic performance in the hydrogenolysis of other carbonyl compounds(e.g.5-hydroxymethylfurfural,benzaldehyde,and vanillin)to monometallic ones.Such surface oxygen decoration strategy endows bimetallic NiCu nanocatalysts a great application potential in the catalytic conversions of biomass-derived compounds containing carbonyl groups.2.The construction of oxygen vacancies promoted CoNi bimetallic catalyst and its performance in the hydrodeoxygenation of vanillinConstructing surface defective structures(e.g.oxygen vacancies)on metal catalysts may alter their surface electronic properties,thus controlling the absorption and activation of reactant molecules and resultantly governing their catalytic activity.Herein,a series of bimetallic CoNi nanocatalysts were fabricated to be employed in the hydrodeoxygenation(HDO)of lignin-derived vanillin to produce methylcyclohexanol(MCYL).It was demonstrated that surface CoOx-decorated CoNi nanoparticles(NPs)could be generated from Co-Ni-Al layered double hydroxide precursors.The as-fabricated bimetallic CoNi nanocatalyst with the Co/Ni atomic ratio of 2:1 exhibited an unprecedented catalytic HDO performance with a nearly 100%yield of MCYL and an ultrahigh turnover frequency of 1303 h-1 under mild reaction conditions(200℃and 1.0 MPa hydrogen pressure).XPS spectra and in situ FT-IR absorption results demonstrated that the introduction of Co into bimetallic CoNi NPs was beneficial to the formation of favorable electron-rich CoO species and abundant surface defective CoOx species.Combining with density functional theory(DFT)calculations and experimental results,it was revealed that surface oxygen vacancies stemming from CoOx species significantly promoted the adsorption and activation of reactants,especially vanillin and 2-methoxy-4-methylphenol intermediate,and meanwhile,surface electron-rich CoO species on CoNi NPs could favor the activation of oxygen-containing groups.Correspondingly,the HDO could proceed rapidly via direct deoxygenation process of the carbonyl group or the methoxy group,with the assistance of double active hydrogen species originating from molecular hydrogen and isopropanol solvent,greatly accelerating the multi-path tandem reactions.The present findings provide an advanced approach for designing high-performance non-noble-metal catalysts applied in the catalytic HDO transformation of various biomass derivatives.3.Construction of CoFe bimetallic catalyst and its performance on 5-hydroxymethylfurfural transfer hydrogenationDeveloping a low-cost transfer hydrogenation catalyst and applying it to 5-hydroxymethylfurfural transfer hydrogenolysis to synthesize biofuel is a challenging topic in the field of energy catalysis.Although the traditional alcohol hydrogen sources used for transfer hydrogenation has greatly reduced the cost,it causes a significant increase in the cost of product separation.In this study,CoMgFe-LDHs precursors were used to synthesize bimetallic CoFe series catalysts with rich defects through topological transformation parameter control.The catalysts can realize the catalytic transfer hydrogenolysis of 5-hydroxymethylfurfural by using formic acid as the hydrogen source and avoid the subsequent products separation steps.The highest yield of 2,5-dimethylfuran can reach up to 90%.XPS results prove that abundant oxygen vacancies exist on the surface of the optimal catalyst,which is conducive to the occurrence of the reverse Mars-van Krevelen reaction to quickly complete the hydroxymethyl hydrogenolysis and maintain the stability of the catalyst.Meanwhile,although the CoFe alloy phase exists in the catalysts,there is no metallic species exist on its surface,which greatly avoids the activation and hydrogenation of the furan ring.The catalysts also have a similar catalytic performance in the preparation of 2-methylfuran by hydrogenolysis of furfural.In addition,In addition,the catalyst can adapt to various alcohol hydrogen sources,such as isopropanol,2-butanol,cyclohexanol,etc.This study provides a new idea for low-cost biomass catalytic transfer hydrogenolysis and has good application prospects.