The NH3-SCR activities of a series of extruded and calcined VOx/ZrO2-SO4 - sepiolite catalysts were determined. The pore structures were heavily influenced by the clay content with macropore sizes ranging from 50 to >1000 nm. Mechanical strength and SCR activity measurements suggested that 25% w/w sepiolite is the optimal catalyst composition. © 2010 Elsevier B.V. All rights reserved.