Abstract: A series of Cs^- salts of heteropolyacids(HPW₁₂, HSiW₁₂) were synthesized. The Hammett function H₀ was determined in order to investigate the acid strength. Their acid contents were measured by acid-base titration and NH₃-TPD respectively; both Bronsted and Lewis acidic sites were observed by monitoring the IR spectra of adsorbed pyridine. The specific surface areas were determined by BET-method. The acid catalytic activity of various salts was also investigated using the esterification of HAc and n-butyl alcohol as a test reaction. The results showed that the Hammett functions H₀ of Cs_xPW series were more strong than that of Cs_zSiW series, while the acidic strength and acid contents decreased with the amount of alkali metal. What is more interesting is that the samples in which their Cs contents are x=2.5 have a maximum surface area. It was confirmed that, not the acid contents on the surface but in the bulk are responsible for the catalytic activity. The reaction seems to be a pseudoliquid phase process.

Key words: solid salt of heteropolyacid, acidity, esterification