Exhaust emission control

Beyond the catalytic ignition point there is a rapid increase in catalytic performance with small increases in temperature. A measure of catalyst performance has been the temperature at which 50% conversion of reactant is achieved. For carbon monoxide this is often referred to as CO. The catalyst light-off property is important for exhaust emission control because the catalyst light-off must occur rehably every time the engine is started, even after extreme in-use engine operating conditions. 

On-Board Diagnostics. State of California regulations require that vehicle engines and exhaust emission control systems be monitored by an on-board system to assure continued functional performance. The program is called OBD-II, and requires that engine misfire, the catalytic converter, and the evaporative emission control system be monitored (101). The U.S. EPA is expected to adopt a similar regulation. 

M. J. Heim rich, L. R. Smith, andj. Kitowski, Cold-Start IPydrocarbon Collection for Advanced Exhaust Emission Control, SAE 920847, Society of... 

Once an undesirable material is created, the most widely used approach to exhaust emission control is the appHcation of add-on control devices (6). Eor organic vapors, these devices can be one of two types, combustion or capture. AppHcable combustion devices include thermal iaciaerators (qv), ie, rotary kilns, Hquid injection combusters, fixed hearths, and uidi2ed-bed combustors catalytic oxidi2ation devices flares or boilers/process heaters. Primary appHcable capture devices include condensers, adsorbers, and absorbers, although such techniques as precipitation and membrane filtration ate finding increased appHcation. A comparison of the primary control alternatives is shown in Table 1 (see also Absorption Adsorption Membrane technology). 

Examples of multi-disciplinary innovation can also be found in the field of environmental catalysis such as a newly developed catalyst system for exhaust emission control in lean burn automobiles. Japanese workers [17] have successfully merged the disciplines of catalysis, adsorption and process control to develop a so-called NOx-Storage-Reduction (NSR) lean burn emission control system. This NSR catalyst employs barium oxide as an adsorbent which stores NOx as a nitrate under lean burn conditions. The adsorbent is regenerated in a very short fuel rich cycle during which the released NOx is reduced to nitrogen over a conventional three-way catalyst. A process control system ensures for the correct cycle times and minimizes the effect on motor performance. 

Figure 1. Principle of 3-way exhaust emission control. Catalyst efficiencies measured in the laboratory with a steady feed stream composition at various simulated air/fuel ratios. Catalyst 0.042 wt % Pt/0.018 wt % Kh/alumina.

Belton, D. N. and Taylor, K. C. (1999) Automobile exhaust emission control by catalysts , Curr. Opin. Solid State. Mater. Sci., 4, 97. 

Augmented-plane-wave method, 34 246 Austemite, decarburization of, 21 332-334 Autocatalysis, 25 275, 34 15, 36 Automobile exhaust emission control, 34 275, 278... 

Since 1962 rare earths have been used to stabilize zeolite cracking catalysts for the petroleum industry (1, 2. Until recently this application to catalysis has been the only commercially significant one. Currently, however, a number of new applications of potential commercial significance are appearing. One of the most important of these is the use of cerium in catalysts for automobile exhaust emission control. We will emphasize this application in our review without neglecting other applications. 

Hough, A. M and C. Reeves, Photochemical Oxidant Formation and the Effects of Vehicle Exhaust Emission Controls in the U.K. The Results from 20 Different Chemical Mechanisms, Atmos. Environ., 22, 1121-1135 (1988). 

Promoters are added to Pt catalysts because the promoted catalyst with modified electronic properties leads to a decrease in the activity for coke formation and also in the rate of metal sintering. Several promoted systems have been reported in the literature including for environmnetal pollution (vehicle exhaust emission) control and some are summarized here. 

Pt-Rh/AROs catalysts are widely used in automotive-exhaust emission control. In these systems, Pt is generally used for the oxidation of CO and hydrocarbons and Rh is active for the reduction of nitric oxide to N2. HRTEM and AEM show two discrete particle morphologies and Pt-Rh alloy particles (Lakis et al 1995). EM studies aimed at understanding the factors leading to deactivation, surface segregation of one metal over the other and SMSI are limited. There are great opportunities for EM studies, in particular, of surface enrichment, and defects and dislocations in the complex alloy catalysts as sites for SMSI. 

SAE International. Diesel exhaust emission control, SP-1860, ISBN 0-7680-1396-8 (2004). 

Important operational factors include vehicle weight, road gradient, vehicle load and the use of auxiliary equipment such as air conditioning, the thermal state of the engine and exhaust emission-control system, and the way in which a vehicle is driven (e.g. speed, or the so-called dynamics of driving). 

In order to protect health and the environment, vehicle exhaust emission standards will continue to be tightened in the EU, and increasing numbers of vehicles will be fitted with the latest exhaust emission-control technologies. By 2020 about one quarter of the total mileage in EU-27 is likely to be covered by cars and trucks certified to Euro 5/V, and more than half by vehicles certified to Euro 6/VI, according to scenarios examined in the LIFE + EC4MACS project (www. ec4macs.eu). 

Monolithic materials are frequently subjected to substantial thermal gradients (thermal shocks) in startup and shutdown, as in auto exhaust emission control. Frequent thermal shocking causes the washcoat to lose adherence due to the expansion difference between it and the monolith. This is most pronounced when the monolith is metallic. 

Several of the early oxide studies have already been mentioned in the introduction. The copper-alumina oxidation catalyst, which finds applications for the synthesis of glyoxal from glycol and as the principal component of base-metal formulations for automobile exhaust emission control, has... 

AECC is an international association, based in Brussels, whose members are European companies in the business of making the technologies for automobile exhaust emissions control. The members are Allied Signal Environmental Catalysts, Coming, Degussa, Emitec, Engelhard Technologies, Johnson Matthey, NGK Europe and Rhone-Poulenc Chimie. 

However, besides exhaust emission control - Fig. 2 - various other aspects in engine development have to be taken into account. The most challenging parameters for the diesel engine are noise, vibration harshness (NVH) control and the necessary technology versus cost required for competitive performance. 

Application of Oxygen Sensors for Exhaust Emission Control... 

Since the introduction of the exhaust emission controls in the US in the midseventies, catalyst technology has developed steadily and the European practice reflects the state of the art. The composition of a typical European catalyst, the operating conditions and performance are given in the following Table 4. 

H.D. Schuster, J. Abthoff and C. Noller, Concepts of Catalyst Exhaust Emission Control for Europe, SAE paper 852095. 

The principle components of modern exhaust emission control catalysts are identified. They comprise (a) a ceramic substrate, (b) a high surface area wash coat, (c) base metal promoters and/or stabilisers and (d) platinum group metals either singly or in combination. 

G. Kim, Ceria Promoted Three Way Catalysts for Auto Exhaust Emission Control, Ing.Eng.Chem.Prod.Res.Dev. 21(1982)267-274. 

Platinum Catalysts for Exhaust Emission Control The Mechanism of Catalyst Poisoning by Lead and Phosphorus Compounds... 

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