Donor acceptor properties of alumina modified with lithium cations were studied by ESR of paramagnetic complexes of adsorbed anthraquinone. The results were compared with the data on negative ion emission (exoemission) accompanying the decomposition of isopropyl alcohol in the adsorption layer. The data on the activity measured by the pulse microcatalytic technique in isopropyl alcohol decomposition are discussed. Small additives of lithium were found to promote catalytic activity of the samples. The role of acid and basic sites in isopropyl alcohol decomposition was discussed.Alkaline metals often exist as admixtures in Al 2 O 3 based catalysts and exert a substantial effect on the acid base properties of the surface and, hence, on the selectiv ity of catalytic processes. Alumina modified with lithium cations is being studied as both a catalyst by itself 1,2 and a support for the nickel and manganese supported cata lysts. 3,4 Modification is usually carried out by the impreg nation method, and either hydroxide 2,5 or a thermally unstable salt (nitrate 3 or acetate 6 ) is applied as a lithium compound. In the present work, the ESR and exoemission (EE) methods are used to study the acid base properties of the Li + /Al 2 O 3 catalyst surface. ESR spectroscopy of paramagnetic complexes of adsorbed anthraquinone pro vides detailed information on the structure and concen tration of electron acceptor sites. 7 The method of low temperature (-269-420 °С) EE of negative charges gives data on the content of electron donor sites. 8 In the present work, we studied how a modifying lithium additive can influence the activity of the Li + /Al 2 O 3 catalysts in the decomposition of isopropyl alcohol and change their donor acceptor properties.
ExperimentalCatalysts were prepared by the impregnation of γ Al 2 O 3 with an aqueous solution of lithium nitrate followed by drying and calcination in air at 450 °С for 4 h and then at 600 °С for 4 h. The catalysts with a content of 0.4-4 mmoles of Li + (g of Al 2 O 3 ) -1 were obtained in this way (Table 1). The surface coverage was estimated under the assumption that each Li + ion occupies the ion area equal to (2r) 2 , where r = 0.068 nm (see Ref. 9). Then the monolayer corresponds to a coverage of 5.41•10 19 Li + m -2 or 89.8 mmol m -2 .The phase composition was determined by X ray diffraction analysis on a DRON 3M diffractometer using Cu Kα radiation.The specific surface was measured on a GKh 1 gasometer using the chromatographic method. At first, low temperature adsorption (-196 °С) of nitrogen was carried out (using an N 2 -He mixture containing 6 mol.% N 2 ), then nitrogen was desorbed at room temperature, and the surface area was deter mined from the area of the desorption peak.Prior to anthraquinone adsorption, the samples were sub jected to thermovacuum treatment at 470 °С in air for 2 h and in vacuo (10 -5
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