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

Abstract

Research highlights: {yields} New triple-layer Dion-Jacobson layered perovskite solid solutions synthesized. {yields} New series of Ta-doped layered perovskite solid acids, HCa{sub 2}Nb{sub 3-x}Ta{sub x}O{sub 10}. {yields} New series of Sr-doped layered perovskite solid acids, HCa{sub 2-x}Sr{sub x}Nb{sub 3}O{sub 10}. {yields} Layered perovskites with highest Ta content are weaker solid acids than HCa{sub 2}Nb{sub 3}O{sub 10}. -- Abstract: Dion-Jacobson type layered perovskites such as A'Ca{sub 2}Nb{sub 3}O{sub 10} (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 Ta{sup 5+} for Nb{sup 5+} and of Sr{sup 2+} for Ca{sup 2+} in A'Ca{sub 2}Nb{sub 3}O{sub 10}. We have prepared and characterized three new solid solutions: KCa{sub 2}Nb{sub 3-x}Ta{sub x}O{sub 10}, RbCa{sub 2}Nb{sub 3-x}Ta{sub x}O{sub 10}, and RbCa{sub 2-x}Sr{sub x}Nb{sub 3}O{sub 10}. 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 HCa{sub 2}Nb{sub 3-x}Ta{sub x}O{sub 10} and HCa{sub 2-x}Sr{sub x}Nb{sub 3}O{sub 10} compounds. Intercalation studies with n-hexylamine and pyridine were carried out to gauge the relativemore » Bronsted acidities across the HCa{sub 2}Nb{sub 3-x}Ta{sub x}O{sub 10} series, and we determined that materials with the highest tantalum contents are weaker acids than the parent compound HCa{sub 2}Nb{sub 3}O{sub 10}. Preliminary intercalation studies with pyridine for the HCa{sub 2-x}Sr{sub x}Nb{sub 3}O{sub 10}.yH{sub 2}O solid acids, however, showed no significant difference in acidity with varying strontium content.« less