The selective catalytic reduction (SCR) of NOx emissions by hydrocarbons (HCs) using a silver (Ag)-based catalyst offers significant advantages over conventional SCR systems that rely on ammonia reductants and vanadium-based catalysts. However, the conversion rate of SCR is influenced by several factors, among which catalyst poisoning is a major concern. Toxic metals such as sodium (Na), potassium (K), magnesium (Mg), and calcium (Ca) can degrade catalyst activity and lead to deactivation. Poisoned catalysts suffer from reduced conversion rates and premature deactivation before reaching their intended operational lifespan. In particular, calcium poisoning results in the formation of CaO (calcium oxide), which reacts to produce a CaWO4 compound that severely impairs SCR performance. This study investigates the role of antimony (Sb) in mitigating Ca-induced deactivation in HC-SCR of NOx. Five catalysts with varying Sb loadings were prepared and tested to evaluate Sb's effect on NOx conversion rate at a space velocity of 30,000 h-1. The results demonstrate that Sb effectively suppresses Ca deactivation, enhancing the conversion rate across all engine test conditions. The highest NOx conversion rate (95.88%) was achieved using a catalyst with 3% Sb.