氮改性ZnO-ZrO_(2)/SBA-15催化剂的酸碱性与其催化乙醇合成1,3-丁二烯反应性能的关系

Relationship between the Acid-base Properties of Nitrogen-modified ZnO-ZrO_(2)/SBA-15 Catalysts and Their Catalytic Performance in the Synthesis of 1,3-Butadiene from Ethanol

1,3-丁二烯(以下简称丁二烯)作为化工的重要有机中间体,在石油以及橡胶工业有着广泛的用途.以乙醇为原料生产丁二烯能够解决生产原料不可再生的问题,所以受到越来越多的关注.本工作采用SBA-15为载体,硝酸盐为氧化物前驱体,含氮有机物为助剂,通过水热合成法制备了催化剂,并探究了乙醇合成丁二烯反应过程中,乙醇转化率、丁二烯收率与催化剂酸碱性的关系.具体来说,使用三聚氰胺(M)、三聚氰酸(Ma)、1,10-菲啰啉(Pm)、咪唑(Im)和1,3,5-三嗪(St)为含氮助剂,制备了Zn-Zr/SBA-15+X催化剂.通过对催化剂的活性评价,计算得到乙醇脱氢和脱水、乙醛缩合、Meerwein-Ponndorf-Verley(MPV)反应的活性.根据反应活性和丁二烯收率与催化剂酸碱性(酸碱强度和含量)的变化关系,发现适当数量的弱酸(0.022 mmol·g^(-1))、中酸(0.078 mmol·g^(-1))、中碱(0.055 mmol·g^(-1))和强碱(0.056 mmol·g^(-1))有助于乙醇脱氢反应的发生,过量的弱酸和中酸将导致乙醇的脱水反应.中等数量的中酸(0.078 mmol·g^(-1))和中碱(0.055mmol·g^(-1))有利于乙醛缩合和MPV反应的发生.丁二烯收率与乙醛缩合活性和MPV活性关联较大.三聚氰胺改性的催化剂(Zn-Zr/SBA-15+M)的弱酸、中酸、中碱和强碱含量符合以上的最优数量,因此催化性能最优异:乙醇转化率为99.5%,丁二烯选择性为65.5%,丁二烯产能达到了0.45 gBD·g^(-1)cat·h^(-1).

1,3-Butadiene(hereinafter referred to as butadiene),as an important organic intermediate in the chemical indus-try,has a wide range of uses in the petroleum and rubber industries.Using ethanol as raw material to produce butadiene can solve the non-renewable problem of raw materials,so it has received more and more attention.In this paper,catalysts were hydrothermally synthesized by using SBA-15 as the support,nitrate as the oxide precursor,and nitrogen-containing organic compounds as the additive.And then,the relationship between catalytic performance(ethanol conversion and butadiene yield)and the acid-base properties of catalysts was explored in the synthesis of butadiene from ethanol.Specifically,we used melamine(M),cyanuric acid(Ma),1,10-phenanthroline(Pm),imidazole(Im),and 1,3,5-triazine(St)as nitrogen-containing additives for the preparation of Zn-Zr/SBA-15+X catalysts.Through the activity evaluation of the catalysts,the activities of ethanol dehydrogenation and dehydration,acetaldehyde condensation,and Meerwein-Ponndorf-Verley(MPV)reactions were calculated.Then,by analyzing the dependence of these activities and butadiene yield on the acidity and basicity(the strength and number of acidic/basic sites)of catalysts,we found that appropriate amounts of weak acid(0.022 mmol•g^(-1)),moderate acid(0.078 mmol•g^(-1)),moderate base(0.055 mmol•g^(-1)),and strong base(0.056 mmol•g^(-1))are helpful for the ethanol dehy-drogenation,whereas excess amount of weak acid and moderate acid will lead to the ethanol dehydration.Appropriate amounts of moderate acid(0.078 mmol•g^(-1))and moderate base(0.055 mmol•g^(-1))will favor the acetaldehyde condensation and MPV reactions.The butadiene yield is closely related to the activities of acetaldehyde condensation and MPV.The mel-amine-modified catalyst(Zn-Zr/SBA-15+M)has the optimum amounts of weak acid,moderate acid,moderate base,and strong base in accordance with the above quantities,resulting in the best catalytic performance:99.5%conversion of ethanol,65.5%selectivity of butadiene,and 0.45 gBD•gcat^(-1)•h^(-1) of butadiene productivity.