摘要
Direct photocatalytic coupling of methanol to ethylene glycol(EG)is highly attractive.The reported photocatalysts for this reaction are all metal sulfide semiconductors,which may suffer from photocorrosion and have low stability.Thus,the development of non‐sulfide photocatalysts for efficient photocatalytic coupling of methanol to EG and H2 with high stability is urgent but extremely challenging.Herein,the first metal oxide photocatalyst,tantalum‐based semiconductor,is reported for preferential activation of C−H bond within methanol to form hydroxymethyl radical(•CH_(2)OH)and subsequent C−C coupling to EG.Compared with other metal oxide photocatalysts,such as TiO2,ZnO,WO_(3),Nb_(2)O_(5),tantalum oxide(Ta_(2)O_(5))is unique in that it can realize the selective photocatalytic coupling of methanol to EG.The co‐catalyst free nitrogen doped tantalum oxide(2%N‐Ta_(2)O_(5))shows an EG formation rate as high as 4.0 mmol gcat−1 h−1,about 9 times higher than that of Ta_(2)O_(5),with a selectivity higher than 70%.The high charge separation ability of nitrogen doped tantalum oxide plays a key role in its high activity for EG production.This catalyst also shows excellent stability longer than 160 h,which has not been achieved over the reported metal sulfide photocatalysts.Tantalum‐based photocatalyst is an environmentally friendly and highly stable candidate for photocatalytic coupling of methanol to EG.
乙二醇是非常重要的基础化学品,不仅可以作为合成聚合物(如聚对苯二甲酸乙二醇酯)的重要单体,也可以用作防冻剂和燃料添加剂等,具有广泛的用途.乙二醇的年产量超过2500万吨,目前主要的工业合成路线是由石油衍生的乙烯通过环氧化制环氧乙烷,环氧乙烷再水解制乙二醇.甲醇是一种清洁的平台化合物,不仅可以由天然气和煤炭通过传统的合成气过程生产,也可以由生物质和CO_(2)直接合成.直接以甲醇为原料是合成乙二醇的理想过程,但目前热催化还未实现该过程.通过太阳能驱动的C−H活化和C−C偶联过程,可以实现甲醇直接偶联制乙二醇的理想反应过程.光催化甲醇制乙二醇可以在十分温和的条件下进行,目前已报道的甲醇制乙二醇光催化剂均为硫化物半导体材料,如CdS,ZnS和Zn_(2)In_(2)S_(5),但硫化物存在的光腐蚀和毒性等问题迫使我们去发展一种更加稳定和环境友好的光催化剂.氧化物基半导体材料,如Ta_(2)O_(5),TiO2,ZnO和WO_(3)等,是一类相对硫化物半导体材料更加稳定的光催化材料,然而目前还没有氧化物基半导体光催化剂用于光催化甲醇制乙二醇的报道.本文率先将金属氧化物光催化剂Ta_(2)O_(5),用于甲醇制乙二醇的光催化反应,实现了乙二醇的选择性合成.在单纯的Ta_(2)O_(5)催化剂上,乙二醇选择性可达73%.Ta_(2)O_(5)十分独特,可以实现甲醇的光催化C−C偶联制乙二醇,而其他金属氧化物光催化剂(如TiO2,ZnO,WO_(3)和Nb_(2)O_(5))光催化转化甲醇只生成甲醛和甲酸等C1产物.进一步通过简单、方便的氨气焙烧法,制备了一系列不同氮掺杂量的氧化钽(N-Ta_(2)O_(5))催化剂.在未经助催化剂修饰的氮含量为2.3%的2%N-Ta_(2)O_(5)光催化剂上,乙二醇选择性为71%,生成速率可达4.0 mmol g_(cat)^(−1)h^(−1),约为Ta_(2)O_(5)的9倍,同时显著高于已报道的未经助催化剂修饰的CdS催化剂性能.通过光电
基金
国家自然科学基金(22022201,21972115)。
