Mixed oxides modified with Lewis acids

Enhanced acidity solids including Brpnsted and Lewis acid-modified metal oxides and mixed oxides, as well as metal salts complexed with Lewis acids. 

The developments of the Lewis base-modified zirconia and mixed-oxide containing zirconia as stationary phases for high-performance liquid chromatography (HPLC) are reviewed. In this context, the preparation methods of porous spherical zirconia, and zirconia supports for HPLC based on modification with fluoride, phosphate, phos-phonate, carboxylic acid, phenols, and protein, as well as cyclodextrin derivative, are covered. The application of modified-zirconia in capillary electrochromatography (CEC) is also discussed. 

Mixed oxides derived from thermal decomposition of LDHs have acid-base properties that influence the catalytic behavior of these materials and depend on the molar ratio Mii/m" ions, their diameters, charge, calcination temperature, and synthesis methods [50, 51]. The acid-base centers are highly active centers that participate in numerous reactions. These properties can be modified by the variation of the M /M molar ratio, by isomorph substitution of a part of M that are present in the structure with other divalent metal ions (such as NT, Be, Co, Zn +, Cu +, Mn +, Cr +, and Fe " ) and by isomorph substitution of a part of M" that are present in the structure with other trivalent metal ions (e.g. Ga T Fe T Co T NTT Mn T V T In T Rh T Ru ") [2]. With the increase of the M cation presence the amount of acid centers also increases in mixed oxides. Acidity depends on the nature of the M cations, for instance AP+ cations exhibit higher acidity than Fe +cations [1]. After thermal decomposition of LDHs, mixed oxides are formed that present solid bases. The alkalinity level depends on the synthesis method. Application of the coprecipitation and sol-gel methods leads to the formation of mixed oxides that have base centers of Lewis type with medium strength... 

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