SYNTHESIS AND THEORETICAL STUDY OF HPW CATALYSTS SUPPORTED ON NIOBIA CALCINATED AT 500 AND 600 ºC

Keggin heteropolyacids (HPW) supported on niobia have been considered for both homogeneous and heterogeneous catalysis due to its special features, like the strong Brönsted acidity, low volatility, high activity and high selectivity for various reactions in comparison with mineral acids. Literature reports many different preparation methods for these catalysts through the addition of HPW solutions, in either water or acid, over niobia under stirring. However not much is known about the way how HPW interacts with the support, neither how the temperature influences this interaction. In order to contribute to expand the knowledge on this field we report here a new way of preparing HPW supported catalysts over niobia calcined at 500 and 600 ºC, followed by a theoretical study meant to check the influence of the temperature increase on the adsorption behavior of the catalysts over the support. Our proposed method showed to be an efficient alternative for impregnation of HPW over niobia, while the theoretical results suggest that pseudohexagonal and orthorhombic are the most likely crystalline forms for these catalysts.