What Is SCR Technology?


If you’ve never heard of selective catalytic reduction (SCR), you are most likely not alone. As a feature of industrial boilers and diesel engines, it goes somewhat unheard of in the United States; however, its effects are worthy of notice and praise. As a result of SCR, NOx reduction efficiency rates, as well as the reduction efficiency rates of other harmful pollutants, are significantly higher. Read on for a full description of the process and its impacts and applications.

What Is Selective Catalytic Reduction?

Selective catalytic reduction is an active emissions regulating technology system applied to diesel engines that converts NOx into safe, breathable molecules. This chemical conversion is initiated using a catalyst and a liquid-reductant agent. The most commonly used reductant source is automotive-grade urea, also referred to as diesel exhaust fluid (DEF).

When directed onto an SCR catalyst, DEF is converted into ammonia, which reacts with NOx to create nitrogen, water, and small amounts of CO2. This chemical reaction is dependent on an SCR catalyst, which provides the required oxidizing atmosphere that permits nitrogen oxide reduction to take place.

Why Is SCR Critical?

Alone, SCR NOx emission controls can reduce up to 90 percent of NOx from diesel engine exhaust fumes; however, it does more than reduce NOx. A cost-effective and fuel-efficient technology, it can also prevent high amounts of other harmful diesel emissions, such as particulate matter (PM) by 30 to 50 percent and hydrocarbons by 50 to 90 percent. When integrated with a diesel particulate matter filter, SCR can cut PM by an even higher percentage.

What Are Its Applications?

Before its widespread application into diesel passenger vehicle engines, SCR technology was integrated into industrial boilers to reduce stationary source emissions. It was also used in large marine vessels, such as ferries and cargo vessels. When the EPA revised its emission standards for heavy-duty vehicles and Tier 4 emissions in 2010, SCR helped successfully meet the stringent requirements.