Mixed salts of cesium and ammonium derivatives of 12-tungstophosphoric acid: Synthesis and structural characterization

Abstract

Mixed salts of cesium and ammonium derivatives of H 3PW 12O 40 ((NH 4) x Cs y H 0.5PW) were synthesized by a precipitation/ion exchange method with a different addition order for each cation. The produced salts were characterized by FTIR, XRD, 31P MAS NMR, SEM, pore size and the BET method. FTIR demonstrated that the materials maintained the Keggin structure under all tested conditions. BET results showed that salts formed by proton substitution from ammonium to cesium had much higher surface areas. Characterization by 31P MAS NMR and XRD, demonstrated that the salt structures varied sharply with the degree of hydration. After calcination, the materials were confirmed to have characteristics of solid solutions with random distribution of the cations with similar crystallographic patterns. The primary nanocrystals aggregated to form solids with mesoporous and microporous structures, created by partial unidirectional growth of the nanocrystals during formation of the bigger, round microcrystallites about 0.3–1 μm in size.