Automotive exhaust cleaning

CeC>2/Zr02/La203 Ceramic Automotive exhaust cleaning Jiang et al. [210]... 

To make a fuel-processing reactor out of a microstructured plate heat exchanger, heterogeneous catalysts need to be introduced into the microchannels, usually by wash-coating, similar to the procedure established for automotive exhaust clean-up. 

A typical example of surface coverage optimization is the reaction between CO and O2. A periodic change in the inlet composition has a particularly important application, namely the catalytic automotive exhaust cleaning. The feed to the catalytic monolith changes periodically, both in composition and in temperature. In this way, the highest possible reaction rate according to Equation 9.34 is achieved. 

Ask the average person in the street what a catalyst is, and he or she will probably tell you that a catalyst is what one has under the car to clean up the exhaust. Indeed, the automotive exhaust converter represents a very successful application of catalysis it does a great job in removing most of the pollutants from the exhaust leaving the engines of cars. However, catalysis has a much wider scope of application than abating pollution. 

As an introductory example we take one of the key reactions in cleaning automotive exhaust, the catalytic oxidation of CO on the surface of noble metals such as platinum, palladium and rhodium. To describe the process, we will assume that the metal surface consists of active sites, denoted as We define them properly later on. The catalytic reaction cycle begins with the adsorption of CO and O2 on the surface of platinum, whereby the O2 molecule dissociates into two O atoms (X indicates that the atom or molecule is adsorbed on the surface, i.e. bound to the site ) ... 

One of the most straightforward methods to reduce carbon dioxide emissions is to enhance the fuel efficiency of engines. The three-way catalyst, although very successful at cleaning up automotive exhaust, dictates that engines operate at air-to-fuel ratios of around 14.7 1. Unfortunately, this is not the optimum ratio with respect to fuel efficiency, which is substantially higher under lean-burn conditions at A/F ratios of about 20 1, where the exhaust becomes rich in oxygen and NOx reduction is extremely difficult (Fig. 10.1). 

New reactor technologies are currently under development, and these include meso- and micro-structured reactors or the use of membranes. Among meso-structured reactors, monolithic catalysts play a pre-eminent role in environmental applications, initially in the cleaning of automotive exhaust gases. Beside this gas-solid application, other meso-structures such as membranes [57, 58], corrugated plate or other arranged catalysts and, of course, monoliths can be used as multiphase reactors [59, 60]. These reactors also offer a real potential for process intensification, which has already been demonstrated in commercial applications such as the production of hydrogen peroxide. 

Technical advantage/fimction Ceramic fibres are used in automotive catalytic converters as bearing and adjustment materials for the catalytic converter (monolith), where the chemical reactions for exhaust cleaning take place. They are also used for thermal and acoustic insulation. Series-tested ceramic fibre substitutes for converter-specific usage conditions are not yet available... 

The monolith honeycomb structure is widely used as a catalyst support for gas treatment applications such as the cleaning of automotive exhaust gases and industrial off-gases [1,2]. In these applications, in which large volumetric flows must be handled, monoliths offer certain advantages, such as low pressure drop and high mechanical strength. 

Structured catalysts, mainly monolithic ones, are now used predominantly in environmental applications, first of all in the cleaning of automotive exhaust gases. Monolithic reactors have become the most commonly used sort of chemical reactors several hundred... 

Plasma-Assisted Catalytic Reduction of NOx in Automotive Exhaust Using Pulsed Corona Discharge Cleaning of Diesel Engine Exhaust... 

Platinum and Platinum Alloys Applications. Platinum and platinum alloys are important constituents of catalysts (chemistry, automotive exhaust gas cleaning, fuel cells), sensor materials (thermocouples, resistance thermometers), strong permanent magnet alloys, magnetic and magnetooptical (memory) devices, high temperature and corrosion resistant stmctural parts, and electrical contacts and connecting elements. Classical applications are jewelry and dentistry alloys. 

Automotive Catalytic Converter Catalysts. California environmental legislation in the early 1960s stimulated the development of automobile engines with reduced emissions by the mid-1960s, led to enactment of the Federal Clean Air Act of 1970, and resulted in a new industry, the design and manufacture of the automotive catalytic converter (50). Between 1974 and 1989, exhaust hydrocarbons were reduced by 87% and nitrogen oxides by 24%. 

I. Gottberg and co-workers. New Potential Exhaust Gas Aftertreatment Technologies for Clean CarEegislation, SAE 910849, Society of Automotive Engineers, Warrendale, Pa., 1991. 

It is fair to state that by and large the most important application of structured reactors is in environmental catalysis. The major applications are in automotive emission reduction. For diesel exhaust gases a complication is that it is overall oxidizing and contains soot. The three-way catalyst does not work under the conditions of the diesel exhaust gas. The cleaning of exhaust gas from stationary sources is also done in structured catalytic reactors. Important areas are reduction of NOv from power plants and the oxidation of volatile organic compounds (VOCs). Structured reactors also suggest themselves in synthesis gas production, for instance, in catalytic partial oxidation (CPO) of methane. 

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