Chemical characterization of particulate emissions from diesel engines: A review

Catalytic NOx Abatement Systems for Mobile Sources: From Three-Way to Lean Burn after-Treatment Technologies Pascal Granger* and Vasile I. Parvulescu* Unit e de Catalyse et de Chimie du Solide, UMR CNRS 8181, University of Lille 1, 59655 Villeneuve d’Ascq, France Department of Organic Chemistry, Biochemistry and Catalysis, University of Bucharest, Romania, 412 Regina Elisabeta Boulevard, Bucharest 030016, Romania

Catalytic NOx Abatement Systems for Mobile Sources: From Three-Way to Lean Burn after-Treatment Technologies

Catalytic converters: state of the art and perspectives

The diesel oxidation catalyst (DOC) has been part of diesel exhaust systems since regulations were introduced to limit the amount of harmful emissions released to the environment from diesel engines. The DOC primary functions are oxidation of CO, unburned hydrocarbons, and NO, while active hydrocarbon oxidation can also be used to generate exotherms required for downstream components. This review will describe work that has attempted to understand the reactions, both desired and undesired, that occur over the catalyst. First, the history, configuration, and components of the DOC will be discussed, followed by in-depth coverage of the fundamental reactions that occur over a DOC, including reaction mechanisms, reaction inhibition, and other reactivity effects. Finally, DOC deactivation mechanisms and their effects on the DOC are described. While there is a lot of research literature regarding Pt- and Pd-based catalysts for many different reaction schemes, this review tries to highlight work most relevant to...

Diesel Oxidation Catalysts

Zeolite-based materials for the selective catalytic reduction of NOx with hydrocarbons

This catalyst system simultaneously removes ammonia and enhances net NOx conversion by placing an NH 3 -SCR catalyst formulation downstream of a lean NOx trap. By doing so, the NH 3 -SCR catalyst adsorbs the ammonia from the upstream lean NOx trap generated during the rich pulses. The stored ammonia then reacts with the NOx emitted from the upstream lean NOx trap—enhancing the net NOx conversion rate significantly, while depleting the stored ammonia. By combining the lean NOx trap with the NH 3 -SCR catalyst, the system allows for the reduction or elimination of NH 3 and NOx slip, reduction in NOx spikes and thus an improved net NOx conversion during lean and rich operation.

Catalyst system for the reduction of NOx and NH3 emissions

A method and system for simultaneously regenerating a particulate filter coupled to an internal combustion engine and for desulfating a lean NOx trap disposed downstream of the particulate filter. The method includes adjusting at least one engine operating parameter to maintain a desired air fuel ratio for gases exiting the particulate filter in accordance with a difference between a reference set point air fuel ratio level and the air fuel ratio of gases exiting the particulate filter and wherein the reference set point level is changed between a rich air fuel ratio and a lean air fuel ratio as a function of the air fuel ratio of the gases exiting the lean NOx trap.

Method and system for controlling simultaneous diesel particulate filter regeneration and lean NOx trap desulfation

European Stage III emissions requirements will be difficult to meet for diesel passenger cars if lean NOx catalysts are not available. Current prototype lean NOx technology for diesels consists of Pt based and Cu zeolite catalysts. Both types have been examined for this study. The former is most active at low temperatures, approximately 190–250°C. The latter has optimum activity at higher temperatures, usually above 350°C. Maximum flow reactor activity of 40–55% NOx conversion (25 000–50 000/h space velocity) has been measured for Pt catalysts using a synthetic feedgas. During the MVEuro2 driving cycle, 35–40% of mass NOx has been emitted at inlet catalyst temperatures from 120 to 200°C. These temperatures fall below optimum temperatures for current Pt based lean NOx catalysts. For temperatures above 350°C, where Cu zeolite catalysts are active, one vehicle has emitted ca. 30% of mass NOx during MVEuro2. These high temperatures are achieved during high speed, hard acceleration driving; although attained briefly during the MVEuro2 cycle, these high temperature emissions could be a critical contribution under customer driving conditions. Effects of sulfur dioxide (SO2) and space velocity (SV) have been investigated as part of a strategy to optimize NOx removal with lean NOx catalysts. Elimination of feedgas SO2 can lower NOx light off temperature for both Pt and Cu zeolite. Some Pt catalysts do not show this behavior. Additional evaluation of a Cu zeolite catalyst demonstrates that poisoning by feedgas SO2 is reversible during evaluation or aging. This result suggests that if sulfur could be removed from diesel fuel, aged Cu zeolite catalysts could be practical. Decreasing space velocity will help NOx removal over Pt by (i) lowering NOx light off temperature, (ii) lowering the temperature at which peak NOx conversion occurs, (iii) increasing the level of peak NOx conversion, and (iv) widening the temperature window for NOx reduction. For Cu zeolite, decreasing space velocity can help mainly by lowering NOx light off temperature and temperature where maximum NOx conversion starts. Both increased catalyst volume and sulfur removal provide Pt catalysts with a NOx temperature window that coincides better with low temperatures where most NOx mass is emitted. SV effects on lean NOx reduction are explained by discussion of possible mechanistic features.

Lean NOx catalysis for diesel passenger cars: Investigating effects of sulfur dioxide and space velocity

This catalyst system simultaneously removes ammonia and enhances net NOx conversion by placing an NH3—SCR catalyst formulation downstream of a lean NOx trap. By doing so, the NH3—SCR catalyst adsorbs the ammonia from the upstream lean NOx trap generated during the rich pulses. The stored ammonia then reacts with the NOx emitted from the upstream lean NOx trap—enhancing the net NOx conversion rate significantly, while depleting the stored ammonia. By combining the lean NOx trap with the NH3—SCR catalyst, the system allows for the reduction or elimination of NH3 and NOx slip, reduction in NOx spikes and thus an improved net NOx conversion during lean and rich operation.

John Vito Cavataio

Papers

Catalyst system for the reduction of NOx and NH3 emissions

Method and system for controlling simultaneous diesel particulate filter regeneration and lean NOx trap desulfation

Lean NOx catalysis for diesel passenger cars: Investigating effects of sulfur dioxide and space velocity

Method for the reduction of NOx and NH3 emissions

Laboratory screening of diesel oxidation catalysts and validation with vehicle testing : the importance of hydrocarbon storage