Study On Solid Acid Catalysts Al-KIT-6 Catalyzing The Reaction Of Biomass Derivative γ-valerolactone To Butene

Biomass is an abundant and renewable resource of carbon that allows the production of high value-added chemicals and fuels,alleviating the environmental pollution caused by the energy crisis and the transition to fossil energy.Gamma-valerolactone（GVL）can be easily obtained from lignocellulosic biomass.More important,the biomass-derived GVL,through specific solid acid catalysts,can be readily the ring opening and decarboxylation,and then converted into butene.Nowadays,the industrial production of butene is still derived from traditional petroleum cracking technology,which not only has a strong dependence on fossil energy,but also caused serious environmental damage.Hence,it is of great significance to develop the catalytic conversion of GVL to butene.However,underperforming stability,the high price of raw materials,and harsh reaction conditions of the currently reportedγ-valerolactone decarboxylation catalysts limit the large-scale application of butene production.In this research,based on the three-dimensional ordered mesoporous molecular sieve KIT-6,three kinds of aluminum-modified KIT-6 solid acid catalysts with high catalytic activity were synthesized.Not only the structure-activity relationship of the catalysts was analyzed in detail,but also the reaction conditions were optimized,and the reaction mechanism and reaction kinetics of catalytic GVL decarboxylation were systematically studied.The specific content is as follows:First,an ordered three-dimensional mesoporous structure KIT-6 was selected and employed as the catalyst support for GVL to butene.A series of x Al-KIT-6（SG）solid acid catalysts with different Al loadings were synthesized by solid-phase grinding.The mesoporous structure,microscopic morphology,active component distribution and surface acidity of the catalyst were analyzed.The results showed that during the solid-state reaction,the Al species efficiently created a lot amount of Br（?）nsted and Lewis acid sites by isomorphically substituting Si⁴⁺cations in the bicontinuous framework of KIT-6 without destroying its ordered three-dimensional mesoporous structure.Under the optimized reaction conditions of reaction temperature=300℃,reaction time=240 min,and concentration of catalyst=10wt.%,GVL was catalyzed by 4wt%Al-KIT-6（SG）catalyst,which could achieve a butene yield as high as 90.06%.Meanwhile,4wt%Al-KIT-6（SG）catalyst remained relatively good catalytic activity after six cycles of the catalytic reaction.Second,in order to improved the dispersion and effective utilization rate of Al species in KIT-6 zeolite,a series of highly active n Al-KIT-6（WI）were prepared for catalyzing GVL to butene.Aluminum was incorporated into the KIT-6 framework through a simple impregnation method to create acid sites,the acid sites amount and Br（?）nsted/Lewis acid ratio was changed by adjusting the aluminum content.The structure,morphology,surface acidity and acid content of the catalyst were analyzed by various characterization methods.The three-dimensional interpenetrating bicontinuous networks of chiral channel of KIT-6 can offer more sites for Al³⁺injection and allow more reactant molecules diffusion through the three-dimensional pore channels.For 3wt%Al-KIT-6（WI）catalyst,the suitable Br（?）nsted/Lewis acid ratio（1.04）and large amount of weak acid sites(0.35 mmol·g^-1)played an important role in the GVL decarboxylation,which endowed 3wt%Al-KIT-6（WI）excellent performance.Over the catalyst,the GVL conversion and butene yield can reach to99.68%and 94.28%at 300℃,respectively.The corresponding Ea was as low as86.97 k J·mol^-1.Moreover,3wt%Al-KIT-6（WI）also exhibited an outstanding regenerable performance for cycle tests.It was found that the presence of proper amount of water is beneficial to the conversion of GVL to butene by inhibiting the deposition of carbon.It means that the 3wt%Al-KIT-6（WI）catalyst has a very great application potential.Finally,in order to highlight the pore advantage of the catalysts,the KIT-6-4T with big windows were prepared using TMB as pore expanding agents.A series of n Al-KIT-6-4T（WI）catalysts were prepared by an improved wet impregnation method.It is proved by various characterizations that the pore structure of the catalyst after pore expansion was highly disordered,and the pore size was about 7.8nm.The increase of pore size further improved the mass transfer efficiency of reactants and products.The impregnation of Al species also efficiently isomorphically substituting Si⁴⁺cations in the framework of KIT-6-4T.Under the optimized reaction conditions of reaction temperature=300℃,reaction time=240min,and concentration of catalyst=10 wt.%,as high as 93.78%yield of butene can be obtained over the 3wt%Al-KIT-6-4T（WI）catalyst,and it also exhibited good catalytic activity at low reaction time and catalyst dosage.After nine cycles of experiments,3wt%Al-KIT-6-4T（WI）also exhibited an outstanding regenerable performance.