合成3-乙氧基丙酸乙酯的K_2O/Al_2O_3催化剂活性组分流失途径研究

Study on Active Site Leaching of K_2O/Al_2O_3 Catalysts in Ethyl 3-Ethoxypropionate Synthesis

以γ-Al_2O_3为载体,KNO_3为前驱体,制备了不同负载量的固体碱催化剂K_2O/Al_2O_3,并用于丙烯酸乙酯(EA)和乙醇加成制备3-乙氧基丙酸乙酯(EEP)反应研究。XRD、FT-IR、N_2吸附-脱附和CO_2-TPD表征结果表明,K_2O/Al_2O_3具有强弱两种碱性位,分别是KNO_3高温焙烧下分解生成的强碱性位K_2O和KNO_3与载体相互作用形成的弱碱性位K-O-Al;提高KNO_3负载量可增加催化剂碱量,但破坏载体结构,降低催化剂比表面积和孔容。加成反应结果表明,30%(wt)K_2O/Al_2O_3具有最高的催化活性,当反应温度为70℃,乙醇和EA摩尔比为6:1,催化剂用量为EA的10%(wt)时,EA的转化率为53.6%,EEP的选择性为98.8%。重复性实验表明,强碱性位中的K_2O与乙醇发生反应生成乙醇钾,进一步溶解于反应液,导致活性位流失,催化剂重复使用活性显著降低。将流失的钾再次浸渍负载到失活催化剂上,可以恢复失活的催化剂活性。因此,开发直接稳定乙醇钾的固体碱催化剂是重要的研究方向。

Solid alkaline catalysts K2O/Al2O3with different loading ratios were prepared usingγ-alumina as asupport and KNO3as a precursor,which were used in ethyl3-ethoxypropionate synthesis.XRD,FT-IR,N2adsorption-desorption and CO2-TPD results reveal that the catalyst has two alkaline sites.The strong alkalinesite(K2O)is derived from KNO3decomposition while the weak one(K-O-Al)is from the interaction betweenγ-alumina and KNO3.The increase of KNO3enhances overall basicity of the catalyst,but it breaks the supportby decreasing its specific surface area and pore volume.When K2O loading is30%(wt),reaction temperature is70℃,mole ratio of ethanol/ethyl acrylate is6:1and catalyst usage is10%(wt)of ethyl acrylate,53.6%of ethylacrylate can be converted to EEP with selectivity of98.8%.However,recycling tests reveal that K2O canirreversibly react with ethanol to form potassium ethoxide that subsequently dissolves in the reaction solution,which results in deterioration of catalytic performance in the following cycles.Reloading of equimolar K2Oonto the used catalyst can effectively regenerate the deactivated catalyst.Therefore,solid alkaline catalysts with permanently immobilized potassium ethoxide are of great interests.