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Cluster models for the interaction of HCl with non-polar surfaces of γ-Al2O3
A348 Surface Science 286 (1993) 333-345 North-Holland
Cluster models for the interaction of HC1 with non-polar surfaces
of 7-A1203 Marina Lindblad ~ and Tapani A. Pakkanen ~ ~ Microchemistry Ltd., P.O. Box 45, SF-02t5l Espoo, Finland b Department of Chemistry, University of Joensuu, P.O. Box t11, SF-8010I Joensuu, Finland Received 1 September 1992; accepted for publication 30 December 1992 The mechanism of interaction of HCI with microcrystaUine y-AI20 3 was studied with a quantum chemical frozen c~re mt~thod Cluster models were constructed for Lewis and Br6nsted sites on non-polar (100) and (110) crystal planes of alumina exposing both aluminum and oxygen ions. The configuration of the adsorption site (AI-O) was defined by the coordination numbers of the aluminum and oxygen ions. Models with 3- and 2-coordinated oxygen ions were considered to represent perfect and defect crystal sites, respectively. The interaction modes studied were associative adsorption on coordinatively unsaturated cations (Al-site). dissociative adsorption on adjacent cation-anion pairs (AI-O-sites), and exchange reactions with OH groups. 'The relativc importance of different interaction mechanisms was evaluated by comparing the calculated stabilization energies of these interaction modes at different surface site configurations. The highest stabilization energies were obtained to~ dissocialwc adsorption of HCI on defect crystal sites of alumina. This was also the only case where an influence of the coordination1 number of the aluminum ion was observed. The stabilization energy for dissociative adsorption was also influenced by thc cca~rdination number of the oxygen ion. Dissociation of HC1 will most probably follow the associative adsorption on an aluminum ion at a defect AI-O-site, but associative and dissociative adsorption of HCI are competitive processes at perfect crystal sites. The ~e~ction w~th hydroxylated surfaces is feasible but, like associative adsorption, structure insensitive.
Surface Science 286 (1993) 346-354 North-Holland
Classical theory of the dielectric function for an inhomogeneous electron gas Hideo Nitta, Shigeru Shindo Department of Physics, Tokyo Gakugei University, Koganei, 7?)kyo 184, Japan
and Mitsuo Kitagawa Department o.f Electronics and Information Technology; North Shore College, SONY Institute of H~gher Educatto,~, ..~tsugl 243, Japan Received 26 August 1992; accepted for publication 30 January 1993 We develop a classical eleetrodynamical theory of the dielectric function for an inhomogeneous electron gas. qhe dielectric function in the high-frequency approximation (HFA) derived by Kitagawa is obtained in a simple manner. It is shown that, in an inhomogeneous electron gas, two different definitions of the dielectric function do not coincide with each other because of the breakdown of the translational invariance~ Using our present method, we can calculate the dynamical potential for an arbitrary electron density that is very difficult to obtain by using other methods. We also describe analytic dielectric functions both for the HFA taking account of a higher-order correction and for the static limit.
Cluster models for the interaction of HC1 with non-polar surfaces
of 7-A1203 Marina Lindblad ~ and Tapani A. Pakkanen ~ ~ Microchemistry Ltd., P.O. Box 45, SF-02t5l Espoo, Finland b Department of Chemistry, University of Joensuu, P.O. Box t11, SF-8010I Joensuu, Finland Received 1 September 1992; accepted for publication 30 December 1992 The mechanism of interaction of HCI with microcrystaUine y-AI20 3 was studied with a quantum chemical frozen c~re mt~thod Cluster models were constructed for Lewis and Br6nsted sites on non-polar (100) and (110) crystal planes of alumina exposing both aluminum and oxygen ions. The configuration of the adsorption site (AI-O) was defined by the coordination numbers of the aluminum and oxygen ions. Models with 3- and 2-coordinated oxygen ions were considered to represent perfect and defect crystal sites, respectively. The interaction modes studied were associative adsorption on coordinatively unsaturated cations (Al-site). dissociative adsorption on adjacent cation-anion pairs (AI-O-sites), and exchange reactions with OH groups. 'The relativc importance of different interaction mechanisms was evaluated by comparing the calculated stabilization energies of these interaction modes at different surface site configurations. The highest stabilization energies were obtained to~ dissocialwc adsorption of HCI on defect crystal sites of alumina. This was also the only case where an influence of the coordination1 number of the aluminum ion was observed. The stabilization energy for dissociative adsorption was also influenced by thc cca~rdination number of the oxygen ion. Dissociation of HC1 will most probably follow the associative adsorption on an aluminum ion at a defect AI-O-site, but associative and dissociative adsorption of HCI are competitive processes at perfect crystal sites. The ~e~ction w~th hydroxylated surfaces is feasible but, like associative adsorption, structure insensitive.
Surface Science 286 (1993) 346-354 North-Holland
Classical theory of the dielectric function for an inhomogeneous electron gas Hideo Nitta, Shigeru Shindo Department of Physics, Tokyo Gakugei University, Koganei, 7?)kyo 184, Japan
and Mitsuo Kitagawa Department o.f Electronics and Information Technology; North Shore College, SONY Institute of H~gher Educatto,~, ..~tsugl 243, Japan Received 26 August 1992; accepted for publication 30 January 1993 We develop a classical eleetrodynamical theory of the dielectric function for an inhomogeneous electron gas. qhe dielectric function in the high-frequency approximation (HFA) derived by Kitagawa is obtained in a simple manner. It is shown that, in an inhomogeneous electron gas, two different definitions of the dielectric function do not coincide with each other because of the breakdown of the translational invariance~ Using our present method, we can calculate the dynamical potential for an arbitrary electron density that is very difficult to obtain by using other methods. We also describe analytic dielectric functions both for the HFA taking account of a higher-order correction and for the static limit.