SCR Catalysts

SCR catalyzers are used in order to decrease nitrogen dioxide emissions (NO_x = NO + NO₂) according to the so-called SCR process. SCR stands for Selective Catalytic Reduction and designates a process by which harmful nitrogen dioxides are converted selectively, i.e. targeted to a suitable catalyzer. In case of HJS, the development of this technology began as early as in the middle of the 1990’s.

Functioning method

The exhaust gas of diesel engines usually includes oxygen (O₂) in surplus. In order to enable the reduction of nitrogen dioxides under these conditions, a reducing agent which acts selectively is required, which converts the nitrogen dioxides targeted to nitrogen (N₂) and water (H₂O). A diluted solution of urea (trade name AdBlue®) is used as reducing agent here, which is decomposed in the exhaust gas and forms the active ammonia reducing agent (NH3) in this case.

The classical SCR catalyzer includes V2O₅ as an active component. However, due to the volatility of this active component at very high temperatures, as can occur for example in case of a particle filter regeneration, in past years catalyzers on zeolite base have come to the fore.

A decisive fact for the performance of the SCR system, as well as the activity of the catalyzer, is the optimum processing of the reducing agent AdBlue^®, which must be injected into the exhaust gas system as spray so that no deposits are formed. Furthermore, the released ammonia must be routed to the SCR catalyzer in an ideally distributed form.

To overcome this, HJS has developed various application-specific solution approaches, which consider the respective operating conditions, possibly autonomously controlled.

Area of application

The SCR system is used both in the private car and commercial vehicle sectors and the technology is widely used to reach Euro VI or EPA 2010 emissions standards. Many Non Road diesel engines also use this type of technology to reach Stage V which will be introduced in 2019 affecting the construction, marine, agricultural and forestry industries. Further plans are also underway which will mean that the rail industry will also be required to comply with stringent emission levels. The HJS SCR system is available for a wide range of applications for both the Original Equipment and retrofit markets.