New solid acids in the triple-layer Dion–Jacobson layered perovskite family

Dion–Jacobson type layered perovskites such as A′Ca2Nb3O10 (A′ = K, Rb, H) have continued to be of great interest due to their compositional variability, rich interlayer chemistry, and wide range of physical properties. In this study, we investigated the range and effects of substitutional doping of Ta5+ for Nb5+ and of Sr2+ for Ca2+ in A′Ca2Nb3O10. We have prepared and characterized three new solid solutions: KCa2Nb3−xTaxO10, RbCa2Nb3−xTaxO10, and RbCa2−xSrxNb3O10. These materials all readily undergo proton exchange to form two new series of hydrated solid acid phases, which in most cases can be dehydrated to form stable HCa2Nb3−xTaxO10 and HCa2−xSrxNb3O10 compounds. Intercalation studies with n-hexylamine and pyridine were carried out to gauge the relative Brønsted acidities across the HCa2Nb3−xTaxO10 series, and we determined that materials with the highest tantalum contents are weaker acids than the parent compound HCa2Nb3O10. Preliminary intercalation studies with pyridine for the HCa2−xSrxNb3O10·yH2O solid acids, however, showed no significant difference in acidity with varying strontium content.