Adsorption of CH-acids on magnesia -: An FTIR-spectroscopic study

被引:54
作者
Huber, S [1 ]
Knözinger, H [1 ]
机构
[1] Univ Munich, Inst Phys Chem, D-80333 Munich, Germany
关键词
adsorption; CH-acids; FTIR-spectroscopy; magnesia; basicity;
D O I
10.1016/S1381-1169(98)00255-6
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
C-H acids including monofluoro-, trifluoro- and trichloromethane, as well as acetylene and methylacetylene were tested as probe molecules for basic sites on MgO by FTIR-spectroscopy. Adsorption structures, frequency shifts, and the applicability of various probes are discussed. Acetylene and methylacetylene undergo H-bonding interactions with Lewis-basic sites on the MgO surface. The experimental frequency shift of the CH-stretching modes can be taken as a measure of the strength of the basic sites. Two adsorption complexes are observed for trichloromethane (CHCl3 and CDCl3) with the CH- (CD-) mode being shifted to lower wavenumbers. A red shift of 36 cm(-1) was obtained for the H-bonded O2- ... H-CCl3-complex. In contrast, the stronger CH-acid CF3H forms an adsorption complex in which hydrogen interacts with the basic oxygen sites and simultaneously one of the fluorine atoms is connected with a Mg2+-site. Adsorbed CH3F on MgO retains the C-3v-symmetry and therefore, the most likely adsorption complex is Mg2+ ... F-CH3. (C) 1999 Elsevier Science B.V. All rights reserved.
引用
收藏
页码:117 / 127
页数:11
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