CHARACTERIZATION OF THE PORE STRUCTURE AND MORPHOLOGY OF SOME ION-EXCHANGED 12-HETEROPOLY OXOMETALATES

Monovalent 12-heteropoly oxometalate salts possessing the Keggin anion have been shown previously to undergo ion-exchange modification to various degrees such that the cation composition of the salts was altered. This study reports the results of investigations concerned with determining the effect of the ion-exchange procedure on the pore structure and morphology of the heteropoly salts. The analysis of nitrogen adsorption-desorption isotherms demonstrates that the ion-exchanged salts possess microporous structures. BET surface areas for the K+/NH4+/PW12O40 and K+/NH4+/PMO12O40 series of salts were found to undergo progressive changes as the cation composition was changed. Lattice parameters determined from powder X-ray patterns showed progressive changes as the cation composition was varied for each of the series of salts studied. The evidence suggests that the cation exchange occurs at sites within the microporous network of the 12-heteropoly salts. © 1991.