Chemical Sciences Division Lawrence Berkeley National Laboratory Berkeley, California 94720, United States.
Department of Chemical and Biomolecular Engineering University of California Berkeley, California 94720, United States.
J Am Chem Soc. 2020 Aug 26;142(34):14674-14687. doi: 10.1021/jacs.0c06906. Epub 2020 Aug 12.
Zinc and Yttrium single sites were introduced into the silanol nests of dealuminated BEA zeolite to produce Zn-DeAlBEA and Y-DeAlBEA. These materials were then investigated for the conversion of ethanol to 1,3-butadiene. Zn-DeAlBEA was found to be highly active for ethanol dehydrogenation to acetaldehyde and exhibited low activity for 1,3-butadiene generation. By contrast, Y-DeAlBEA was highly active for 1,3-butadiene formation but exhibited no activity for ethanol dehydrogenation. The formation of 1,3-butadine over Y-DeAlBEA and Zn-DeAlBEA does not occur via aldol condensation of acetaldehyde but, rather, by concerted reaction of coadsorbed acetaldehyde and ethanol. The active centers for this process are ≡Si-O-Y(OH)-O-Si≡ or ≡Si-O-Zn-O-Si-O≡ groups closely associated with adjacent silanol groups. The active sites in Y-DeAlBEA are 70 times more active than the Y sites supported on silica, for which the Y site is similar to that in Y-SiO but which lacks adjacent hydroxyl groups, and are 7 times more active than the active sites in Zn-DeAlBEA. We propose that C-C bond coupling in Y-DeAlBEA proceeds via the reaction of coadsorbed acetaldehyde and ethanol to form crotyl alcohol and water. The dehydration of crotyl alcohol to 1,3-butadiene is facile and occurs over the mildly Brønsted acidic ≡Si-OH groups present in the silanol nest of DeAlBEA. The catalysts reported here are notably more active than those previously reported for both the direct conversion of ethanol to 1,3-butadiene or the formation of this product by the reaction of ethanol and acetaldehyde.
锌和钇单原子被引入脱铝 BEA 沸石的硅醇窝中，分别得到 Zn-DeAlBEA 和 Y-DeAlBEA。然后，这些材料被用于乙醇转化为 1,3-丁二烯的反应。Zn-DeAlBEA 对乙醇脱氢生成乙醛具有很高的活性，而对 1,3-丁二烯的生成活性较低。相比之下，Y-DeAlBEA 对 1,3-丁二烯的生成具有很高的活性，但对乙醇脱氢没有活性。Y-DeAlBEA 和 Zn-DeAlBEA 上生成 1,3-丁二烯不是通过乙醛的羟醛缩合，而是通过共吸附的乙醛和乙醇的协同反应。这个过程的活性中心是 ≡Si-O-Y(OH)-O-Si≡ 或 ≡Si-O-Zn-O-Si-O≡ 基团，与相邻的硅醇基团密切相关。Y-DeAlBEA 中的活性位比负载在二氧化硅上的 Y 位活性高 70 倍，而 Y 位与 Y-SiO 中的相似，但缺少相邻的羟基，比 Zn-DeAlBEA 中的活性位高 7 倍。我们提出，Y-DeAlBEA 中的 C-C 键偶联是通过共吸附的乙醛和乙醇反应形成烯丙醇和水进行的。烯丙醇脱水生成 1,3-丁二烯是容易的，并且在脱铝 BEA 的硅醇窝中存在的轻度 Brønsted 酸性 ≡Si-OH 基团上发生。与之前报道的乙醇直接转化为 1,3-丁二烯或通过乙醇和乙醛反应生成该产物的催化剂相比，这里报道的催化剂活性显著更高。
