Study On Catalytic Hydrogenation Of ?-valerolactone To 1,4-pentanediol And 2-methyltetrahydrofuran

Increasing resource shortages and environmental pollution problems have brought unprecedented challenges to the sustainable development of human society,prompting the traditional economic strategy based on petroleum resources must gradually transition to the development strategy based on renewable resources.In recent years,wind energy,water energy,solar energy and biomass energy have received more and more attention as important renewable resources.As the only renewable carbon source of biomass,its rational and effective development and utilization is the top priority.More importantly,the highly selective catalytic conversion of biomass and its platform molecules to high value-added chemicals is an important means to alleviate the increasingly scarce fossil resources and obtain chemical intermediates.Gamma-valerolactone?GVL?,as a sustainable supply of raw materials for the production of carbon-based chemicals and energy,is considered to be one of the most promising biomass-based platform molecules.In the work,Cu/Al₂O₃ and a series of ZnCu/Al₂O₃ catalysts were prepared by impregnation method and co-deposition method,and high value-added products such as 1,4-pentanediol?1,4-PDO?and 2-methyltetrahydrofuran?2-MTHF?were prepared with?-valerolactone?GVL?as substrate.The physical and chemical properties of the catalyst were determined by XRD,H₂-TPR,XPS,N₂O,TEM,CO₂-TPD and Py-FTIR.The catalytic properties were discussed by the relationship between the activity and selectivity,the metal state and the acid strength of the catalyst.The main results are as follows:?1?The Cu/Al₂O₃ catalyst was prepared by the impregnation method.The Cu loading was 10 wt.%?The mass ratio of Cu to?-Al₂O₃ was 0.1?.A series of ZnCu/Al₂O₃ catalysts were prepared by using the calcined Cu/Al₂O₃ catalyst?Cu loading was fixed at 10 wt.%?and further impregnated with Zn,and the Zn/Cu molar ratio was 0.5².GVL was used as a substrate to prepare high value-added products such as 1,4-PDO and 2-MTHF.It was found that under the conditions of reaction temperature of 200?,hydrogen pressure of 4MPa and reaction time of 3 h,when using Cu/Al₂O₃ catalyst,the conversion of GVL was98%,and the selectivity of 2-MTHF was as high as 92%;However,when using Zn_1.5Cu/Al₂O₃[n?Zn?/n?Cu?=1.5]catalyst,the conversion of GVL was 91%,and the selectivity of 1,4-PDO was as high as 97%.The conversion of Cu/Al₂O₃ catalyst decreased from 98%to 50%after five cycles.The conversion of Zn_1.5Cu/Al₂O₃ catalyst decreased from 91%to 80%after ten cycles.The addition of Zn adjusted the selectivity of Cu/Al₂O₃catalyst and significantly improved the stability.The results showed that the addition of Zn decreased the Lewis acid sites on the surface,inhibited the dehydration of 1,4-PDO to form2-MTHF,and thus obtained 1,4-PDO with high selectivity.In addition,the addition of Zn inhibits the oxidation of Cu⁰ and the transformation of Al₂O₃ to Al?OH?₃,which improved the stability of Zn_1.5Cu/Al₂O₃ catalyst.?2?The catalysts with different Cu/Zn molar ratios were prepared by co-deposition method,and the effect of reduction temperature on the catalytic performance was investigated.Under the reaction conditions of 200?,hydrogen pressure of 4 MPa and reaction time of 2 h,on the bimetallic Cu_0.3Zn/Al₂O₃ catalyst,when the reduction temperature was 200?,the conversion of GVL was 68%,and the selectivity of 1,4-PDO was 71%.When the reduction temperature was increased to 360?,the conversion was slightly increased to 72%,and the selectivity of 1,4-PDO was significantly increased to87%.When the reduction temperature was further increased to 440?,the selectivity of1,4-PDO was further increased to 98%although the conversion was reduced to 63%.For the Cu_0.7Zn/Al₂O₃ catalyst,when the reduction temperature was 200?,the conversion was 89%,and the selectivity of 1,4-PDO was 82%.When the reduction temperature was increased to 360?,the conversion was 90%,and the selectivity of 1,4-PDO was increased to 89%.When the reduction temperature was further increased to 440?,the conversion slightly reduced to 83%,and the selectivity of 1,4-PDO was 91%.For the Cu_1.5Zn/Al₂O₃catalyst,when the reduction temperature was 200?,the conversion was 92%and the selectivity of 1,4-PDO was 61%.Raise the reduction temperature to 360?,the conversion was 89%,and the selectivity of 1,4-PDO was 87%.The reduction temperature was further increased to 440?,the conversion was 88%,and the selectivity of 1,4-PDO was 87%.Based on the above experimental results,we found that in a series of Cu_xZn/Al₂O₃catalysts,increasing the reduction temperature has a significant effect on the hydrogenation activity and selectivity of the catalyst,and with the reduction temperature increases,the activity of the catalyst increases first and then decreases,but with the increase of Cu/Zn ratio,the rate of decrease in activity becomes slower and slower;The selectivity of the product 1,4-PDO show a linear increasing trend with the increase of the reduction temperature.The higher the temperature,the higher the selectivity of 1,4-PDO.The change of the selectivity with temperature did not depend on the Cu/Zn ratio.A suitable reduction temperature?360??can obtain a higher yield of the product.