Synthesis of layered perovskite oxides, ACa2-xLaxNb3-xTixO10 (A = K, Rb, Cs), and characterization of new solid acids, HCa2-xLaxNb3-xTixO10 (0 < x ≤ 2) exhibiting variable bronsted acidity

Gopalakrishnan, J. ; Uma, S. ; Bhat, V. (1993) Synthesis of layered perovskite oxides, ACa2-xLaxNb3-xTixO10 (A = K, Rb, Cs), and characterization of new solid acids, HCa2-xLaxNb3-xTixO10 (0 < x ≤ 2) exhibiting variable bronsted acidity Chemistry of Materials, 5 (1). pp. 132-136. ISSN 0897-4756

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Official URL: http://pubs.acs.org/doi/abs/10.1021/cm00025a025

Related URL: http://dx.doi.org/10.1021/cm00025a025

Abstract

Layered perovskite oxides of the formula ACa2-xLaxNb3-xTixO10 (A = K, Rb, Cs and 0 < x ≤ 2) have been prepared. The members adopt the structures of the parent ACa2Nb3O10. Interlayer alkali cations in the niobium-titanium oxide series can be ion-exchanged with Li+, Na+, NG4+, of H+ to give new derivatives. Intercalation of the protonated derivatives with organic bases reveals that the Bronsted acidity of the solid solution series, HCa[sub 2-x]La[sub x]Nb[sub 3-x]Ti[sub x]O[sub 10], depends on the titanium content. While the x = 1 member (HCaLaNb2TiO10) is nearly as acidic as the parent HCa2Nb3O10, the x = 2 member (HLA2NbTi2O10) is a weak acid hardly intercalating organic bases with pKa ~ 11.3. The variation of acidity is probably due to an ordering of Nb/Ti atoms in the triple octahedral perovskite slabs, [Ca2-xLaxNb3-xTixO10], such that protons are attached to NbO6 octahedra in the x = 1 member and to TiO6 octahedra in the x = 2 member.

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