Establishment Of Multifunctional Catalysis System For In-situ Hydrogenation And Deoxygenation Of Biomass-Derived C=C/C=O Double Bonds

The hydrogenation and deoxygenation of biomass-derived C=C and C=O double bonds is the main route for the production of high-valued chemicals and biofuels.However,this route is usually carried out under high-pressure H₂,causing problems associated with H₂ storage,transportation,and safety risks.The in-situ hydrogenation pathway using alcohols,formic acids,hydrocarbons,etc.as hydrogen donors can reasonably ameliorate the above issues and has been considered as an effective alternative.However,the in-situ hydrogenation catalysts require both outstanding hydrogen donor dehydrogenation and reactant hydrogenation activities,and ensures the two-step reaction to achieve dynamic equilibrium,which greatly increases the difficulty of catalyst design.Precious metal-based catalysts are mostly used,but their catalytic performance is far inferior to those of conventional hydrogenation system that requre H₂ as hydrogen donor.The activity,stability,sequences of tandem reaction and side reaction rate still need to be improved.This dissertation therefore develops several efficient and highly stable non-noble metal-based catalysts for in-situ hydrogenation of furfural and fatty acids with alcohols as the hydrogen donor.The main work is summarized as follows:1)Al₂O₃-supported Cu,Ni and bimetallic Cu-Ni catalysts with different Cu/Ni ratios were prepared by coprecipitation method and used for in-situ hydrogenation of furfural with isopropanol as hydrogen donor.The composition and structure of the as-synthesized catalysts were analyzed by XRD,H₂-TPR,TEM,XPS,ICP-OES measurements.It was found that the bimetallic catalyst mainly existed in the form of Cu-Ni alloy.Additionally,the influence of catalyst composition on the reactivity was explored,and the mechanism of bimetallic synergistic catalysis was clarified by comparing their catalytic activity.It was found that the low hydrodeoxygenation activity of furfuryl alcohol over Cu-based catalyst and over-hydrogenation of C=C in furan ring over Ni-based catalyst were the main cause for the low coupling efficiency of multi-step reaction.The selectivity to 2-methylfuran over bimetallic Cu-Ni catalyst was much higher than that obtained by the corresponding single metal catalysts due to its kinetic equilibrium of multistep reactions and absence of side reactions.The reaction conditions such as the type of hydrogen source,catalyst addition,reaction temperature,reaction time,reusability,etc.were then optimized.The total yield of 2-methylfuran and 2-methyltetrahydrofuran obtained was up to 83%at 230℃ for 4 h.More importantly,the yield of 2-methylfuran kept almost stable even after 4 times of usage;2)Al₂O₃-supported Cu,Ni and bimetallic Cu-Ni catalysts from 1)were employed for the in-situ hydrogenation and decarboxylation of oleic acid in methanol-water system due to their superior performance on in-situ hydrogenation of furfural,and the relative catalytic system was proposed.The experimental results show that bimetallic Cu-Ni/Al₂O₃ catalyst performs much better than the corresponding single metal counterparts and yield of the heptadecane was more than 90%under optimized reaction conditions.The kinetic equilibrium of multistep reactions and the absence of side reactions are responsible for the excellent performance of the bimetallic catalyst as revealed by C2H4,C3H8,acetic acid-TPD measurements.Meanwhile,the inferior decarboxylation activity of Cu-based catalysts and the rapid pyrolysis reaction over the Ni-based catalysts due to their strong adsorption of C-C/C=C bonds were the main reasons for their relative lower catalytic activity.Moreover,the reusability of Cu-Ni/Al₂O₃ catalysts was investigated,and the main reasons for the decreased catalytic activity revealed by XRD,DSC-TGA,TEM,CO-TPD and BET measurements were the inferior hydrothermal stability of Al₂O₃ carrier.Finally,the reaction pathway over Cu-Ni bimetallic catalyst was proposed through the exploration of the reaction behaviors of different intermediate products;3)The catalytic activity of Cu-Ni/Al₂O₃ catalyst in the above catalytic system decreased remarkably after use due to the inferior hydrothermal stability of Al₂O₃ support.Therefore,the ZrO₂ carrier with better hydrothermal stability was synthesized by coprecipitation method and employed for in-situ hydrogenation and decarboxylation of oleic acid in methanol-water system.A series of characterization methods such as XRD,H₂-TPR,TEM,EDS-mapping,ICP-OES revealed that bimetallic Cu-Ni/ZrO₂ catalyst is the mixed m-ZrO₂ and t-ZrO₂ supported Cu-Ni alloy.The catalytic mechanism over Cu-Ni/ZrO₂ is similar to that of Cu-Ni/Al₂O₃ in 2).The catalytic activity of Cu-Ni/Al₂O₃ is much higher than that of Cu-Ni/ZrO₂ due to the higher surface area of Al₂O₃,which is beneficial to the sintering-resistant dispersion of Cu-Ni alloy.The good reusability of Cu-Ni/ZrO₂ catalyst is mainly attributed to the strong interactions between Cu-Ni alloy and ZrO₂ and superior hydrothermal stability of ZrO₂;4)In the previous chapter,it was found that alkanes were hardly produced from the deoxygenation of fatty acids/alcohols over Cu-based catalysts in methanol-water system.Considering that,the technical route on production of fatty alcohols from in-situ hydrogenation of fatty acids over non-precious Cu-based catalyst under the methanol-water system was proposed.Additionally,the influence mechanism of carrier and reaction mechanism of in-situ hydrogenation of fatty acids into fatty alcohols were discussed.The effects of carriers were also investigated by comparing the catalytic activity of Cu/ZrO₂,Cu/MgO and Cu/Al₂O₃,Among these,Cu/Al₂O₃ with the highest Cu dispersion,the smallest Cu particle size and highest CO₂ adsorption capacity displayed the highest catalytic activity.Additionally,the physical and chemical properties of different Cu-based catalysts were revealed by XRD,H₂-TPR,TEM,EDS-mapping,BET,CO-TPD and CO₂-TPD measurements.Also,it was found that the in-situ H was mainly derived from the cleavage of C-H and O-H bonds in methanol,and the water gas shift reaction of the intermediate CO.Finally,the reusability of the different catalysts was investigated where Cu/ZrO₂ catalyst showed the best performance;5)Cu/m-ZrO₂ and Cu/t-ZrO₂ catalysts were synthesized by different preparation methods,and the interaction between Cu and t-ZrO₂ could be effectively adjusted,leading to even deeper investigation of the effectiveness of carrier structure on catalytic activity.It was found that the catalytic activity of Cu/t-ZrO₂ with strong metal-support interaction was much better than Cu/m-ZrO₂ and Cu/t-ZrO₂ without strong metal-support interaction towards the aqueous-phase reforming of methanol,hydrogenation of fatty acids,and in-situ hydrogenation of fatty acids.The crystal structure of the different catalysts was characterized by XRD and TEM techniques.In addition,the metal-support interactions in different Cu/t-ZrO₂ was measured by H₂-TPR,EDS-mapping,CO-DRIFTs and XPS techniques.The adsorption of acetic acid and H on t-ZrO₂ was significantly stronger than that of m-ZrO₂ as evidenced by acetic acid-TPD,acetic acid-DRIFTs and DFT calculation approaches,revealing the reason for the low activity of Cu/m-ZrO₂.More importantly,the DFT calculation results further collaborated the claim that Cu/t-ZrO₂ with strong metal-support interaction exhibited outstanding in-situ hydrogenation activity due to the presence of rich Cu/t-ZrO₂ interface.