摘要
用D_2^(18)O在Rh-TiO_2/SiO_2催化剂上进行了原位化学截取反应及原位^(18)O同位素交换反应,所得产物中含有氘代乙酸,表明乙烯酮是一种反应中间体;产物中有含^(18)O的乙醇、乙醛、乙酸,表明乙烯酮等C_2含氧前驱中间体与重氧水发生了^(18)O同位素交换反应。按照乙烯酮与水进行同位素交换的模式,只要进行2～3次的交换,就可以解释Katzer等用^(13)C^(16)O/^(12)C^(18)O与H_2反应观察到的产物乙醇的同位素杂组结果,而无须假设乙烯酮异构成能量较高的环氧乙烯然后进行同位素交换,使乙烯酮机理更合理。再次肯定了我们提出的“CO缔合-卡宾-乙烯酮-乙酰基-乙醇(醛)”的机理。
The mechanism of syngas conversion to ethanol over Rh-TiO2/SiO2 catalyst was studied by adding D218O to syngas as agent for trapping and 18O isotopic exchange of intermediates. After reaction, products on catalyst were purged off with nitrogen containing MeOH, collected in a liquid-nitrogen cold trap, and analyzed with GC-MS. Compounds including CH3CH218OH, CH3CH2OH, CH3CH18O, CH3CHO, CH2DC18O OMe, CH3COOMe, CH2DCOOMe, and CH3C18OOMe were found. The existence of the first two esters reveals CH2 C=O and CH3C = O to be intermediates which reacted with D218O and MeOH to form respective esters, the existence of the last two esters and 18O-ethanol and -acetaldehyde means the isotopic exchange of intermediates with D218O. Based on the model of isotopic exchange of ketene with water produced in the reaction, the isotopic distribution of the product of Katzer's experiment conducted with 13C16O/12C18O-H2 can also be obtained. This can be done by statistical calculation based on 2-3 times isotopic exchange between ketene and water without Katzer's hypothesis of existence of higher energy ketene isomer oxirene for isotopic exchange. Therefore, the ketene mechanism, 'metalloxycarbe-ne-carbene-ketene-acetyl-ethanol ( acetaldehyde ) ' , proposed by us previously appears to be reasonable.
出处
《分子催化》
EI
CAS
CSCD
1991年第1期16-23,共8页
Journal of Molecular Catalysis(China)
基金
国家自然科学基金
