The effect of sulphating zirconia on the selective catalytic reduction of NO by CH4 in oxygen excess of Pd catalysts has been investigated. Since both the acidity and the Pd dispersion both contribute to the activity and selectivity of these catalysts a series of samples were prepared with different sulphate contents but maintaining the amount of Pd constant. Significant chemical and textural changes were caused by sulphating the zirconium hydroxide starting material, which lead to a clear improvement in the catalytic behaviour. A medium sulphate doping (approximate to 4 wt.% expressed as SO42-) was found to be the most adequate to promote activity and selectivity in these Pd-sulphate zirconia based catalysts. (C) 2006 Elsevier B.V. All rights reserved.