摘要
用IR光谱研究了SO_4^(2-)/ZrO_2超强酸体系脱水和脱吡啶过程中的结构变化,实验结果表明,含水样品的表面硫物种中SO键呈离子键(Ⅰ)和共价双键(Ⅱ)两种形式,随脱水程度增加,Ⅰ逐渐变成Ⅱ。吸附吡啶样品的SO键亦有Ⅰ、Ⅱ两种形式,且随脱吡啶程度增加,Ⅰ逐渐变成Ⅱ。在脱水或吡啶过程中,SO键Ⅱ的振动频率移向高频,表明SO键键级增加,共价性质加强。无水的SO_4^(2-)/ZrO_2样品表面只有L酸位,无B酸位。吸水后部分L酸位可按1∶1转变成B酸位,但体系中L酸量始终高于B酸量。根据键级、键长和氧电荷计算结果,还讨论了样品吸水后产生的B酸位结构。
Structural changes in the SO2-4 ,/ZrO2 superacid system caused by desorption of preadsorbed water and pyridine were studied with IR spectroscopy. The experimental observations show that SO bonds in the surface sulfur species of the hydrated samples exist in two forms, i, e. , the ionic SO bond (Ⅰ) and the covalent SO double bond( Ⅱ). Ⅰ transforms into Ⅱ with the removal of water from the sample. The presence of two types of SO bonds and the transformation from Ⅰ to Ⅱ were also observed in samples preadsorbed with pyridine. In addition, the asymmetric stretching frequency of SO bond Ⅱ shifts to a higher frequency during desorption of preadsorbed water or pyridine, suggesting that the bond order and the double-bond character of the SO bond are increased. It is found that only L acid sites are present on the surface of the carefully dried SO2-4/ZrO2 sample. After adsorbing water , some L acid sites may transform into B acid sites in the ratio of 1:1. However, the number of L acid sites in the sample is always higer than that of B acid sites. The structure of the B acid sites formed after hydration has been discussed by using the results of changes in bond order, bond length and partial charge on oxygen.
出处
《高等学校化学学报》
SCIE
EI
CAS
CSCD
北大核心
1993年第5期658-662,共5页
Chemical Journal of Chinese Universities
基金
中国石油化学工业总公司资助课题
关键词
超强酸
红外光谱
硫酸根
氧化锆
SO2-4/ZrO2 system, Superacid, L acid, B acid. Structure
