Urea-SCR: a promising technique to reduce NOx emissions from automotive diesel engines

An overview is given of the selective catalytic reduction of NOx by ammonia (NH3‐SCR) over metal‐exchanged zeolites. The review gives a comprehensive overview of NH3‐SCR chemistry, including undesired side‐reactions and aspects of the reaction mechanism over zeolites and the active sites involved. The review attempts to correlate catalyst activity and stability with the preparation method, the exchange metal, the exchange degree, and the zeolite topology. A comparison of Fe‐ZSM‐5 catalysts prepared by different methods and research groups shows that the preparation method is not a decisive factor in determining catalytic activity. It seems that decreased turnover frequency (TOF) is an oft‐neglected effect of increasing Fe content, and this oversight may have led to the mistaken conclusion that certain production methods produce highly active catalysts. The available data indicate that both isolated and bridged iron species participate in the NH3‐SCR reaction over Fe‐ZSM‐5, with isolated species being the ...

https://www.tandfonline.com/doi/pdf/10.1080/01614940802480122

The State of the Art in Selective Catalytic Reduction of NOx by Ammonia Using Metal‐Exchanged Zeolite Catalysts

Trends in NOx abatement: A review

Atmospheric amines - Part I. A review

Diesel engines have high efficiency, durability, and reliability together with their low-operating cost. These important features make them the most preferred engines especially for heavy-duty vehicles. The interest in diesel engines has risen substantially day by day. In addition to the widespread use of these engines with many advantages, they play an important role in environmental pollution problems worldwide. Diesel engines are considered as one of the largest contributors to environmental pollution caused by exhaust emissions, and they are responsible for several health problems as well. Many policies have been imposed worldwide in recent years to reduce negative effects of diesel engine emissions on human health and environment. Many researches have been carried out on both diesel exhaust pollutant emissions and aftertreatment emission control technologies. In this paper, the emissions from diesel engines and their control systems are reviewed. The four main pollutant emissions from diesel engines (carbon monoxide-CO, hydrocarbons-HC, particulate matter-PM and nitrogen oxides-NOx) and control systems for these emissions (diesel oxidation catalyst, diesel particulate filter and selective catalytic reduction) are discussed. Each type of emissions and control systems is comprehensively examined. At the same time, the legal restrictions on exhaust-gas emissions around the world and the effects of exhaust-gas emissions on human health and environment are explained in this study.

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The pollutant emissions from diesel-engine vehicles and exhaust aftertreatment systems

The hydrolysis of isocyanic acid (HNCO) was investigated on various oxidic catalysts, including TiO2, V2O5/TiO2, and V2O5−WO3/TiO2. The kinetics were studied using powdered samples in a microreactor. The conversions of HNCO are high even at the high space velocities (106 h-1) and low temperatures (150 °C) used in the tests. The highest rate for the hydrolysis of HNCO was found on pure TiO2 powder, while the addition of vanadia and tungsta decreased the activity slightly. To compare the rate of HNCO hydrolysis with the rate of the SCR reaction, uncorrected first-order rate constants were calculated for both reactions using the integral equation for a plug flow reactor. For a catalyst sample containing both WO3 and V2O5, the rate constant for hydrolysis of HNCO at low temperatures is about 2 orders of magnitude higher than the respective rate constant for the SCR reaction, whereas at high temperatures, the rate constants are of comparable magnitude. The apparent activation energy of the hydrolysis reaction ...

M. Kleemann

Papers

Urea-SCR: a promising technique to reduce NOx emissions from automotive diesel engines

Hydrolysis of Isocyanic Acid on SCR Catalysts