Study On The Preparation Of Alkyl Levulinate And γ-Valerolactone From Furfural Over Zr-based Solid Acids With Tunable Acidic Sites

As the important renewable carbon resource,biomass can replace fossil resources to produce carbon-based chemicals,materials and liquid fuels.Biomass resources are rich in sources and reserves.Rational development and utilization of biomass can be expected to reduce the emissions of global carbon dioxide greenhouse gas,decrease the destruction of ecological balance,and adapt to the requirements of energy transformation.Biomass can be converted into various platform compounds,the high value-added chemicals,materials and fuels through the chemical catalytic conversion of biomass.Furfural(FF)is one of the few biomass-based platform compounds that has achieved industrial scale production.FF can be usually directly extracted from hemicellulose components in corn cob and other raw materials through acid catalysis,and its production process is relatively mature.Furfural as a raw material has a wide range of applications in the field of chemical,pharmaceutical,fuel,food and other industries,and it is considered to be one of the most promising biomass-based platform compounds.Alkyl levulinate(AL)and y-valerolactone(GVL)can be prepared by FF through acid-catalyzed alcoholysis and transfer hydrogenation reaction.AL and GVL are regarded as the excellent oxygenated biofuel additives,mixing with gasoline and diesel can effectively improve the performance of exhaust emission.Additionally,AL and GVL could be converted to other high-valued chemicals or fuels through chemical catalysis.Although AL can also be prepared by cellulose or glucose through alcoholysis,FF has high solubility in alcohol systems and few side reactions.Therefore,choosing FF as the substrate to preparate AL and GVL is a more suitable approach for industrial applications.FF usually requires catalytic reduction,alcoholysis and continuous reduction to prepare AL and GVL.In a reduction system using hydrogen as a hydrogen source,FF is prone to excessive reduction reactions,and hydrogenation catalysts usually cannot simultaneously catalyze the alcoholysis of FF to prepare AL.In addition,the cost of hydrogen storage,use,and management is high.The reduction reaction of carbonyl compounds such as FF can also be achieved by a transfer hydrogenation route with fatty alcohols as the in-situ hydrogen donor.The transfer hydrogenation reaction can be carried out by Lewis acid sites,and the alcoholysis reaction requires Br?nsted acid sites.Aiming at the problem that the catalyst connot integrate Lewis and Br?nsted acid sites in the conversion of FF to AL and GVL,we designed and synthesized the multifunctional solid acid catalysts to synergistically catalyze the preparation of AL and GVL by FF via transfer hydrogenation and alcoholysis.Firstly,a series of zirconium-aluminum bimetal oxide supported SBA-15 catalysts(Zr-Al/SBA-15)were designed and synthesized in this paper,and Zr-Al/SBA-15 was successfully catalyzed the one-pot conversion of FF to ethyl levulinate(EL).ZrO2 with Lewis acid sites meets the requirement for the transfer hydrogenation of FF to furfuryl alcohol(FA),Al2O3 with Br?nsted acid sites is charge of alcoholysis of FA to EL.We have found that the ratio of Lewis and Br?nsted acid sites could be flexibly tuned via adjusting the ratio of ZrO2 to Al2O3,thereby the catalytic performance of the catalyst was also regulated.Zr-Al/SBA-15(30:10)has a moderate L/B acid ratio and excellent catalytic performance when the mass ratio of ZrO2 and Al2O3 is 30:10.92.8%FF conversion and 67.2%EL yield(71.2%EL selectivity)were achieved under the condition of 453 K and 3 h in ethanol.It should be pointed out that this is the highest yield in the researches of non-noble metal-catalyzed one-pot conversion of FF to EL so far.Secondly,the multifunctional zirconium phosphate supported SAPO-34 catalysts(ZPS-x)were designed and prepared,and the catalytic performance on the one-pot conversion of FF to GVL in isopropanol was studied in depth.The conversion of FF to GVL requires a three-step acid-catalyzed process of transfer hydrogenation,alcoholysis and re-transfer hydrogenation,which places higher requirements and challenges on acid catalysts.Low amount of Lewis acid sites cannot catalyze the transfer hydrogenation of FF or intermediate AL to produce FA or GVL,and the excessive Br?nsted acid sites will promot side reactions of FF/FA to form humins.The Lewis acid sites are derived from the active center Zr,and the Br?nsted acid sites are provided by-P(OH)n.In addition,SAPO-34 is also rich in Lewis and Br?nsted acid sites.L/B acid ratio were adjusted by changing the Zr/P ratio,and then the catalytic activity of ZPS-x catalys can be controled.When the Zr/P ratio is 1(ZPS-1.0),100%FF conversion and 80%GVL selectivity were obtained under the reaction conditions of 423 K,18 h and 443 K,8 h.Otherwise,the catalyst with excellent recycling performance could achive 65%selectivity of GVL after 6 recycles.The catalytic activity could be basically restored after regeneration.