Abstract
AbstractThe catalytic reduction of nitrogen oxides (NOx) under lean-burn conditions represents an important target in catalysis research. The most relevant catalytic NOx abatement systems for Diesel engine vehicles are summarized in this short review, with focus on the main catalytic aspects and materials. Five aftertreatment technologies for Diesel NOx are reviewed: (i) direct catalytic decomposition; (ii) catalytic reduction; (iii) NOx traps; (iv) plasma-assisted abatement; and (v) NOx reduction combined with soot combustion. The different factors that can affect catalytic activity are addressed for each approach (e.g. promoting or poisoning elements, operating conditions, etc.). In the field of catalytic strategies, the simultaneous removal of soot and NOx using multifunctional catalysts, is at present one of the most interesting challenges for the automotive industry.
Highlights
Air pollution from mobile sources, such as cars and trucks, contributes to a great extent to air quality problems and induces health risks in rural, urban, and industrialized areas in both developed and developing countries
The stringent regulation limits on both nitrogen oxides (NOx) and particulates matter (PM) are forcing the automotive industry, one hand, to maximize engine control to reduce pollutant emissions, and on the other hand to pile up a number of costly catalytic converters; this results in rather high pressure drops, complex control features, inefficiency linked to considerable weight and space consumption and elevated costs
The progressive requirements for fuel-efficient diesel cars highlight the problem of the necessity of removing NOx under lean-burn conditions in order to satisfy current legislation
Summary
Air pollution from mobile sources, such as cars and trucks, contributes to a great extent to air quality problems and induces health risks in rural, urban, and industrialized areas in both developed and developing countries. The features of the Diesel fuel itself, and of the Diesel engine operating conditions (airto-fuel ratios greater than 22) lead to the formation of both gaseous (NOx, CO, HC) and solid/liquid (PM) pollutants.[2] These Diesel engine emissions may originate from the incomplete combustion of fuel, from operating conditions that favor the formation of particular pollutants, or from the oxidation of nitrogenand sulfur-containing compounds present in the fuel which are not hydrocarbons.[3, 4] A common engine management strategy to control NOx emissions is Exhaust Gas Recirculation (EGR).
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