THERMAL DECOMPOSITION OF Pd DOPED 12-TUNGSTOPHOSPHORIC ACID AND SOME OF ITS CESIUM SALTS

The H3PW12O40 center dot xH(2)O and its acid salts with Cs are known acidic catalysts. The thermal decomposition of Pd doped H3PW12O40 and its acid salts with Cs occurs by the constitutional water release over 573 K. The thermal decomposition process could be explained based on the microstructure model for cesium acidic salts as agglomerates with a core consisting of Cs3PW12O40 crystallites covered of acid layers, but in this case the layers of acid contain PdHPW also. No important differences were observed between composition, structure and thermal behaviour of the two series of Pd doped compounds obtained by changing the order of reactants adding. The apparent activation energy of constitutional water loss was determined using the Standard Test Method for Decomposition Kinetics by Thermogravimetry-E 1641-04. The Pd doping causes a significant decrease of apparent activation energy, especially for acid salts with lower Cs content because it supports the release of constitutional water.