The ammonia SCR activity of a series of rare earth vanadates supported over TiO2-WO3-SiO2 was investigated after thermal treatment in the temperature range 700-750 degrees C and their properties studied by XRD, TPR, BET and HRTEM analysis. It was found that the thermal stability of the catalyst is remarkably higher than that observed in traditional vanadia-based materials, with the rare earth vanadate being able to suppress the unfavorable transformation of anatase to rutile and the consequent surface area drop. The deNO(x) activity after aging was higher than that observed over V2O5/TiO2-WO3-SiO2 and dependent on the nature of the rare earth element. A group of elements comprising Tb, Er, Dy, Sm and Gd showed excellent resistance to deactivation and high activity after aging while a second group with Ce, La, Nd and Pr was more sensitive to thermal treatment and less active. This was correlated to their position in the periodic table and to their ability to alter the characteristics of the V-O bond and the acid/base surface properties. (C) 2011 Elsevier B.V. All rights reserved.