[en] Highlights: • SCR performance decreases after durability testing, especially at high engine speeds. • NOx conversion efficiency of deteriorated catalysts decreases at high temperatures. • Deterioration of catalysts in front of SCR is more serious than in rear. • Deterioration is due to a decrease in specific surface area and catalyst components. • Anatase-to-rutile transformation of TiO₂ does not happen, not cause of deterioration. -- Abstract: The durability of V₂O₅-WO₃/TiO₂ selective catalytic reduction (SCR) catalysts for heavy-duty diesel engines was evaluated based on 500 h SCR durability tests conducted using B20 fuel (20% v/v biodiesel + 80% v/v petroleum diesel). The fresh and deteriorated SCR catalysts were characterized by X-ray fluorescence, X-ray diffraction, and Brunauer-Emmett-Teller surface area measurements to investigate the deterioration mechanism of the catalysts. The results show that the SCR de-NOx performance is degraded after SCR durability testing, particularly at high engine speeds. The NOx conversion efficiency of the deteriorated SCR catalysts decreases at temperatures above 400 °C but remains high at temperatures between 250 and 400 °C. The catalyst characterization results reveal that the deterioration in the de-NOx performance is not owing to anatase-to-rutile transformation of TiO₂, but because of a decrease in the specific surface area and the loss of the catalyst components, which are greater in the front cross section of the SCR than in the rear cross section. For a given catalyst cross section, the decrease in the specific surface area exhibits a positive correlation with the flow rate of the exhaust gas.