SCR stands for which phrase?

• A. Selective Catalytic Reduction
• B. Sulfate Catalytic Reduction
• C. Static Catalytic Reduction
• D. Systematic Catalytic Reduction

Answer: (A)

SCR stands for Selective Catalytic Reduction, an emissions-control method that lowers NOx in exhaust by passing it over a catalyst while a reductant such as ammonia or urea is injected. The “selective” part means it specifically targets NOx, and the “catalytic” part means the reaction occurs on a catalyst surface to convert NOx into harmless nitrogen and water. This technology is widely used on diesel engines to meet smog and air-quality standards. The other phrases don’t describe this established NOx-reduction process.