Selective catalytic reduction is the process used to lessen NOx emissions hence controlling air pollution rates. The process involves the conversion of emissions into water and nitrogen gas. The process uses a catalyst in the form of ammonia or air, which is injected into the exhaust pipes hence holding the NOx gases. Once the gases have mixed thoroughly as the emissions pass through the catalytic bed NOx is reduced. The catalysts used are only meant to reduce the NOx but do not affect it. The by-product resulting from the reaction between urea and the emissions is carbon dioxide. Selective catalytic reduction usually reduces NOx emissions by 70 to 95%.

Power plants usually discharge huge volumes of the NOx gases as the power that is used is acquired from ignition of fuels. With this technique, these emissions have been reduced considerably. The process is made up of the reactor chamber, the catalyst bed, which holds the catalyst modules as well as an Ammonia injection grid system.

Once the ammonia steam or air gets injected into the exhaust pipes that contain the NOx gases, it passes through the catalytic bed, reducing the nitrogen oxides and non malignant nitrogen gas. The catalyst technique uses urea, aqueous ammonia and anhydrous ammonia. All these catalysts have their disadvantages, but urea is the most common. This technique is acknowledged for its ability to reduce the harmful emissions by a great percentage.

The disadvantage in this technique arises when there is ammonia slip. This is when ammonia that has not been used finds its way into the air. This can occur when the required temperatures not maintained or if more that the required ammonia is released into the system. An additional disadvantage comes by when ammonium bisulphate or sulfate are emitted. These result from the excess ammonia combining with the sulfates contained in the air. These sulfates have been proven to cause inflammations and coughs.

Proper use of selective catalytic reduction has various benefits. For instance, coal fired boilers fitted with the system have been able to reduce 60% to 65% of NOx emissions. Gas fired utilities on the other hand have achieved more than 90% reductions.

The system originated in the USA, founded by the Engelhard Corporation. It was yet to be tested by then. Later developments of the system were made in Japan and the US during the early 60s’. By then the research laid more focus on the agents of catalyzation that could be more durable and cheaper. The first system was then installed by the IHI Corporation in 1978.

The most favored reducing agents are produced from different ceramic materials, which are used as carriers. Such include titanium oxide. However, the active catalytic components are obtained from metals like vanadium and zeolites. They can also be obtained from precious metals. Catalysts from vanadium and other base metals are not highly durable but those obtained from zeolites can withstand high temperatures. Plate type catalysts are the best when it comes to withstanding temperatures. However, they are very expensive.

Best content writer in association with Cormetech Inc., the leading producer of titania-based ceramic honeycomb catalyst for NOx emissions control and NOx reduction used in Selective Catalytic Reduction (SCR) systems for air pollution control.