Carbon monoxide emission, thermal

Figure 3. Carbon monoxide emissions effect of noble metal content on durability performance of thermally optimized noble metal mixture...

The chemical and thermal characteristics of PGE make them highly useful as catalysts in a wide variety of industrial, chemical, electrical and pharmaceutical processes (Johnson Matthey 2007). Their use as catalysts in automotive catalytic converters to reduce noxious emissions from the burning of fossil fuels has undoubtedly been one of the most far-reaching and important applications. Automobiles have been equipped with catalytic converters since 1975 and 1986 in the US and Europe, respectively. Initially, Pt and Pd were used to reduce hydrocarbon and carbon monoxide emissions. Since the early 1990s, Rh has also been used in various combinations and ratios with Pt and Pd in three-way catalytic converters to reduce emissions. PGE appear to be emitted together with alumina particles from the washcoat as a result of various chemical, physical and... 

Emonts reported the operation of catalytic burners for hydrocarbons and methanol/ anode off-gas dedicated to fuel processing operations [555]. The burners were designed for thermal loads of up to 11.5 kW. Palladium catalyst deposited onto porous ceramic fibre was used for natural gas combustion. Only 0.5 g palladium was required for the burner, which was water-cooled by a concentric tube-bundle cooler mostly through radiation losses. At 11.5-kW power output, carbon monoxide emissions were below 10 mgkWh , while NOj emissions were around 2 mgkWh . The methanol burner worked with a platinum catalyst and showed lower NOj emissions of 0.4mgkWh. ... 

Reduced air preheat and reduced firing rates lower peak temperatures in the combustion zone, thus reducing thermal NO,. This strategy, however, carries a substantial energy penalty. Emissions of smoke and carbon monoxide need to be controlled, which reduces operational flexibility. 

Automobile and Hydrocarbon Emissions. The oxidation of carbon monoxide and hydrocarbons is catalyzed by platinum/palladium/rhodium on alumina. If catalyst poisons such as lead and phosphorus are not present, the major problems become initiation of oxidation at low temperature, thermal stability at high temperature, resistance to thermal schock, and a high external surface area catalyst configuration. 

The heat of reaction, H, for carbon oxidation to carbon monoxide is 2340 cal/g. k is the gas thermal conductivity evaluated at the arithmetic mean of particle and gas temperatures e is the particle emissivity and assumed here to be unity and is the Stefan-Boltzmann constant. 

The CEN/TC 295 draft standard prEN 13240 [1] is based on measurements of efficiency and flue gas emissions at a nominal burning rate. The emission factors are based on concentration measurements of the pollutants in the due gas. The efficiency is calculated indirectly by the flue loss method taking into account the thermal due gas losses (sensible heat) and the chemical losses (combustible gases, here as carbon monoxide, CO). 

Early emission control methods were based on the use of a thermal reactor for hydrocarbon and carbon monoxide oxidation, combined with exhaust gas recirculation (EGR) for reduction of nitrogen oxide emissions (Fig. 3.2a). Hydrocarbons and carbon monoxide in the hot exhaust fed to the reactor, once heated, were rapidly oxidized to carbon dioxide and water by the additional pumped air which was fed to the reactor (e.g., Eqs. 3.3 and 3.4). 

Carbon dioxide and water are the main products of this reaction. However, incomplete combustion causes some emissions of unbiuned hydrocarbons, as well as intermediate oxidation products such as alcohols, aldehydes and carbon monoxide. As a result of thermal cracking reactions that take place in the flame, especially with incomplete combustion, hydrogen is formed and emitted, as well as hydrocarbons that are different from the ones present in the fuel. 

Noble metal catalysts are highly active for the oxidation of carbon monoxide and therefore widely used in the control of automobile emissions. Numerous recent studies on noble metal-based three-way catalysts have revealed characteristics of good thermal stability and poison resistance(l). Incorporation of rare earth oxides as an additive in automotive catalysts has improved the dispersion and stability of precious metals present in the catalyst as active components(2). Monolith-supported noble-metal catalysts have also been developed(3). However, the disadvantages of noble metal catalysts such as relative scarcity, high cost and requirement of strict air/fuel ratio in three-way function have prompted attention to be focused on the development of non-noble metal alternatives. 

Fresh and thermally aged catalysts containing mixtures of platinum and palladium were laboratory tested for the oxidation of carbon monoxide, propane, and propylene. For both monolithic and particulate catalysts, resistance to thermal deactivation was optimum when palladium content was 80%. Full-scale vehicle tests confirmed these findings. Catalysts of this composition were developed which, on the basis of durability tests at Universal Oil Products and General Motors, appeared capable of meeting the 1977 Federal Emissions Standards with as little as 0.56 g noble metal per vehicle. The catalyst support was thermally-stabilized, low density particulate. 

AA, and IR spectroscopy. Metal analysis may be performed by atomic absorption or emission spectroscopy and their stoichiometric amounts in the carbonyl complexes may be determined. Samples may be digested carefully and cautiously with nitric acid in a fume hood before the determination of metal contents. For mass spectrometric determination the carbonyl complex should be dissolved in an organic solvent, injected onto a GC column and identified from the characteristic mass ions. The carbonyl ligands in the complex may be determined by thermal decomposition of the metal carbonyl followed by analysis of carbon monoxide on a GC-TCD. 

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