Automotive exhaust gas

In the last 15 years, an intense effort has been made to decrease the environmental impact of automotive exhaust gases. More and more severe regulations have pushed... 

Hammer, T. (2002) Non-thermal plasma application to the abatement of noxious emissions in automotive exhaust gases, Plasma Sources Sci. Technol. 11, A196-A201. 

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. 

The composition, temperature and flow amount of automotive exhaust gases vary continuously with driving conditions. The circumstance of the exhaust catalysts exposed is far more different from that in chemical factories. The automotive catalysts are requested to purify infinitesimally small amount of the... 

Because of the rapid developments in the field of heterogeneous catalysis, the material reviewed here is exclusively dedicated to selective oxidations. No attention is given to total oxidations or combustion processes (including the problem of automotive exhaust gases). There is one exception, however the oxidation of sulphur dioxide to trioxide. Work on vanadate catalysts for this reaction is close to research on selective catalysts and therefore included. 

From an environmental point of view the sulphur concentration must be reduced in order to reduce SO2 formation in automotive exhaust gases [1],... 

Nitrous oxide (N20, also known as dinitrogen oxide) is one of the main products of nitric oxide reduction. It is regarded as an undesirable and harmful component of automotive exhaust gases,40 and it is a more harmful greenhouse gas than carbon dioxide, possibly contributing to ozone depletion in the upper atmosphere.6 13 In spite of this, there are still only a few papers... 

Automotive Exhaust Gases in Los Angeles, Vehicle Emissions I. SAE Progress in Technology Series (1964) 6, 7-16. 

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... 

A nice example of cooperation between metal particles and a support with redox properties concerns the three-way catalysts for automotive exhaust gases treatment composed of a noble metal (Pt, Pd, Rh) on a support with ceria additive. The cooperation was put in evidence in the CO/NO/O2 reactions [135-137] and... 

The laboratory reaction system used was a conventional flow system with a tubular fixed-bed reactor as described elsewhere(18). The characteristic feature of this system is its ability to simulate various air to fuel ratios (A/F) of automotive exhaust gases using eight mass flow controllers. In this study, catalytic activity on the catalysts in simulated automotive exhaust gases was measured as a function of X, which is a normalized value of A/F by a stoichiometric one in the simulated exhaust gas, at 300°C and 420,000 h space velocity. The compositions of the simulated exhaust gases for each X are shown in Table 1. Catalytic activity was expressed as percent conversions of NOx(NO+N02), CO, and HC. 

The anthropogenic H2 is emitted into the air in automotive exhaust gases, which contain H2 in the range of 1-5 % by volume. The nature of the oceanic source is not entirely clear but it is probably due to microbiological activity. However, the supersaturation of ocean waters unambiguously indicates hydrogen gas formation there. The emission from soils is caused by the fermentation of bacteria. 

Tlhe catalytic removal of nitrogen oxides from automotive exhaust gases has been the subject of many studies. Catalysts containing at least 20 different metals, alone and in combination, have been tested. We found that the support used in catalyst preparation is as important as the metal, particularly in catalyst selectivity toward nitrogen rather than ammonia in strongly reducing streams. This paper is a report on some of the effects of support chemistry in a fairly well known system, platinum-promoted nickel (I). We also elucidate the pathways of ammonia removal in this system. 

Transition metal ions dispersed in spinel matrices were studied for the decomposition of nitrous oxide (15,16) however, there have been no reports on solid solutions of spinels for augmenting catalytic activity and stability in oxidation reactions. This is a report on work done with transition metal oxide spinels to minimize the first two forms of degradation through formation of solid solutions. Included are studies of various reaction processes involved in catalytic treatment of automotive exhaust gases. 

ZEOLITE CATALYST FOR THE PURIFICATION OF AUTOMOTIVE EXHAUST GASES... 

The catalytic oxidation of ethylene on metal oxides such as RUO2 and Ir02 is generally highly non-selective resulting in the complete oxidation of ethylene to CO2 and H2O (see Eq. 1). In such a case, the catalytic performance can be uniquely characterized by a single reaction rate, e.g., by that of CO2 production, rcoj (mol s ). The catalytic combustion of ethylene is a well-studied model reaction. In fact, ethylene is often used as a model compound for unsaturated hydrocarbon residues in automotive exhaust gases. 

For the conversion of automotive exhaust gases the three-way catalyst (TWC) enables the removal of the three pollutants CO, NO and hydrocarbons ( HC ) in the following manner (Eqs. 10-1 to 10-4) ... 

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