Noble-Metal-Free Catalysts:Design And Its Application In The Hydrogenation Of Biomass Derivatives

With the reduction of fossil resources and environmental problems worldwide,it is urgent to find sustainable and alternative resources.We have paid great attention to biomass and use inedible lignocellulose to produce biofuels and biochemical products.Therefore,the study of related biomass reactions has broad application prospects.γ-butyrolactone（GBL）and ethyl levulinate（EL）are used as the derivatives of biomass platform molecules in biomass and used as research substrates.In this paper,continuous impregnation method was used to prepare Cu La_x/Al₂O₃catalyst and Cu M_0.25/Al₂O₃（M=Y,La,Pr,Nd,Eu,Er,Yb）catalyst doped with different rare earth elements.Andγ-butyrolactone（GBL）and ethyl levulinate（EL）as substrates to prepare 1,4-butanediol（1,4-BDO）and 1,4-pentanediol（1,4-PDO）with high value-added glycol products.Through XRD,H₂-TPR,XPS,N₂O chemical titration,TEM（HRTEM）,CO₂-TPD,NH₃-TPD and CO-DRIFT characterization,the physical and chemical properties of the catalyst’s bulk and surface were determined.The relationship between properties and surface active substances,acid-base properties,activity and selection are discussed.The main results are as follows:1.A series of catalysts Cu La_x/Al₂O₃（x=0,0.1,0.25,0.5）were prepared by continuous impregnation method.γ-butyrolactone is the substrate of hydrogenation reaction to generate 1,4-butanediol.We found that under the conditions of a reaction temperature of 200°C,a hydrogen pressure of 4 MPa and a reaction time of 6 hours,when the Cu/Al₂O₃catalyst is used,theγ-butyrolactone conversion rate is 79.6%,and the main product selectivity is 37.6%The by-product tetrahydrofuran is 60.4%.However,when Cu La_0.25/Al₂O₃catalyst is used,the conversion ofγ-butyrolactone is 94.2%,and the selectivity of 1,4-BDO is as high as 95.5%.After five cycles of the Cu/Al₂O₃ catalyst,the conversion rate dropped from 79.6%to 52.8%.After five cycles of the Cu La_0.25/Al₂O₃catalyst,its conversion rate dropped from 91%to 84%.The addition of La increases the selectivity and activity of the Cu/Al₂O₃ catalyst and significantly improves the stability of the catalyst.The results showed that the addition of La reduced the surface Lewis acid sites and inhibited the dehydration of 1,4-butanediol to form tetrahydrofuran,thereby obtaining highly selective 1,4-butanediol.The synergy between Cu⁰ and Cu⁺（close contact La O_x）is the key to the ring-opening hydrogenation reaction.We speculate that the dissociative adsorption of H₂ can occur at the Cu⁰ position,and then the active H species is transferred to the GBL adsorbed at the Cu⁺-La O_x interface to complete the hydrogenation reaction.Finally,we used a series of five-and six-membered lactones（such asγ-butyrolactone,γ-valerolactone,δ-caprolactone）as substrates,and also obtained highly selective glycol products.2.The Cu M_0.25/Al₂O₃（M=Y,La,Pr,Nd,Eu,Er,Yb）catalysts doped with different rare earth elements were prepared by continuous impregnation method,and the effect of calcination temperature on the catalytic performance was investigated.Different rare earth element Cu M_0.25/Al₂O₃ catalysts are used in the hydrogenation of ethyl levulinate.Under the reaction conditions of 200°C,4 MPa hydrogen pressure and 12 h reaction time,the best catalyst is Cu Nd_0.25/Al₂O₃,the conversion rate is 100%,the selectivity of the main product 1,4-pentanediol is significantly increased to 90%,the selectivity of the by-productγ-valerolactone is 7.4%,and the selectivity of 2-methyltetrahydrofuran is 3.2%.And choose Cu Nd_0.25/Al₂O₃ catalyst,continue to discuss the influence of different calcination temperature（350°C,450°C,550°C,650°C）on the hydrogenation reaction of ethyl levulinate,Cu Nd_0.25/Al₂O₃-450°C shows the best catalytic activity.Through XRD and TPR characterization,combined with the above experimental results,we found that particle size and metal-metal interaction play a key role in catalytic performance.