Irreversible chemical deactivation of state-of-the-art vanadium selective catalytic reduction (SCR) catalysts was investigated using an aftertreatment system from a heavy-duty diesel vehicle for general haulage application. Elemental analysis revealed that Field returned vanadium SCR catalysts had higher phosphorous and zinc concentrations than those from a fresh catalyst. Phosphorous concentration dropped significantly from catalyst inlet to outlet, while zinc concentration remained almost constant. Broadened infrared intensity from V5+=O and W6+=O bonds were observed from contaminated vanadium SCR samples. Anatase phases and crystallite size remained unchanged in the presence of chemical contaminants. Chemical contamination monotonically reduced NH3 storage capability but non-linearly modified acid site distribution and oxidation activity, causing differences in NOx reduction behaviors. Low chemical contamination on vanadium SCR catalyst reduced NOx conversion below 450 degrees C due to the decrease in NH3 storage capacity and oxidation activity. NOx conversion over a sample with high phosphorus concentration was lowered by the weakened NH3 storage capacity below 350 degrees C and the enhanced parasitic NH3 oxidation above 400 degrees C. High levels of phosphorus increased low-temperature NOx conversion compared to low levels of phosphorus due to increase in oxidation capability. (C) 2015 Elsevier B.V. All rights reserved.