Exhaust catalysts gases

SCR systems at stationary diesel engines profit from the high exhaust gas temperatures of about 350-400 C, caused by the usually constant high load operation conditions of the diesel engine. In this temperature window nearly all known SCR catalysts are very active. Moreover, weight and size of the exhaust gas catalyst are usually not strictly limited, which results in a good NO, reduction efficiency (DeNOJ. However, DeNO, is not the only criterion for an SCR catalyst. Further requirements are excellent selectivities regarding NO and urea/ammonia as well as low ammonia slip, which is an undesired secondary emission of the SCR process. Therefore, all SCR catalysts exhibit surface acidity, which is necessary to store ammonia on the catalyst surface and, thus, to prevent ammonia slip. 

Most oil streams in a refinery must be hydrotreated consequently, hydrotreating is the largest application in industrial catalysis based on the amount of material processed per year. On the basis of the amount of catalyst sold per year, hydrotreating catalysts rank third after exhaust gas catalysts and fluid cracking catalysts. 

Identical results have been obtained with platinum and rhodium couples for preparation of model exhaust gas catalysts. 

Hydrogen, preadsorbed on noble metals, is commonly used to prepare bimetallic catalysts by redox reaction. This requires the parent metal to chemisorb hydrogen (Pt, Pd, Rh, Ru, etc.) and to introduce a modifier that is reducible by hydrogen (Cu, Re, Ir, Rh, Pd, Pt, Au, etc.). All combinations of these metals have been prepared and characterized. For example, this technique has been used to prepare model Pt-Re reforming catalysts. Also, Pt-Rh and Pd-Rh were preformed to examine the interaction between platinum and rhodium in exhaust gas catalysts [8-10, 15-20, 21]. 

Exhaust gas catalysts has been widely used since the laimching of the 1970 Clean Air Act in the USA and especially after the introduction of stricter regulations in 1981. At present, one of the fastest growing areas of catalyst-based technology is automotive pollution control. All gasoline-fuelled vehicles sold in the USA, Japan and in the European Community must be equipped with exhaust aftertreatment in order to meet the emission standards. Oxidation catalysts for heavy-duty vehicles have only been used for a short period, but following the tightening emission standards there will be an increased demand for such systems. 

L.J. Pettersson and S.G. JSrSs, Exhaust Gas Catalyst for Alcohol Vehicles, Report 92-265-742, BCFB, Stockholm, Sweden, 1994. 

Fig. 7.5.14 Sensor with brass housing and front side O-ring snap-in design for coolant bypass for exhaust-gas catalyst retrofit control unit...

M. Nonnemann,Metal Supports for Exhaust Gas Catalysts, SAE paper 850131. 

INFLUENCE OF THE POROUS STRUCTURE OF ALUMINA PELLETS AND THE INTERNAL CONVECTIVE FLOW ON THE EFFECTIVE DIFFUSIVITY OF EXHAUST GAS CATALYST... 

To analyse the performance of exhaust gas catalyst (activity and poisoning) the effective diffusivity of six Rhone Poulenc alumina supports is measured by a physical dynamic method in a single pellet string reactor. 

One of the causes of deactivation of the exhaust gas catalyst, in both pellet and monolith form, is clogging by lead, phosphorus and zinc traces contained in exhaust gases. 

The impurities stick to the periphery of particle pores making the gas flow into the catalyst difficult or impossible. This in turn leads to a considerable increase in the diffusion resistances during the catalytic process. One way of fighting this phenomenon is to use double-porosity alumina. Micropores of about 20 nm are always useful to develop the specific surface area necessary for a good dispersion and stability of the catalytic phase. Macropores over 100 nm in diameter help to diffuse the reagents within the particles. However, the proportion of macropores must not be too great, as that would diminish the mechanical properties of the support correspondingly. For this reason, Rhone Poulenc has, since 1974, developed and marketed various exhaust, gas catalyst supports with specific surface areas of 2... 

Influence of the Porous Structure of Alumina Pellets and the Internal Convective Flow on the Effective Diffusivity of Exhaust Gas Catalyst",... 

De-NOx Catalyst [Mitsubishi Kasei] Nitric acid plant exhaust gas catalyst... 

In recent years the continuing refinement of engine management and emission control systems has made a significant contribution to lowering tail pipe emissions from gasoline fuelled cars. In the USA, the penetration of cars with catalyst converters is effectively complete. In Europe penetration is around 20% as only recently there has been a requirement for all new cars to be equipped with an exhaust gas catalyst system. 

The studies of the use of the ion exchanger Metalfix Chelamine of tetraethylenepentamine ligands (1,4,7,10,13 - pentaazatridecane) in the process of recovery, concentration and separation of platinum metal ions, gold and their accompanying elements from the environmental samples, anodic sludges from the electrorefining of copper ores, spent car exhaust gas catalysts, etc. [93-98]. 

Despite present predictions for the number of diesel-powered cars in Europe to increase markedly, discussions on the engineering approach to the control of automobiel emissions have centered on the gasoline motor. Cylinder wall temperature, air-fuel ratios, exhaust gas catalysts, and lead traps were presented and discussed as remedies. Blended fuel, for instance gasohol or synthetic fuels, were not considered because they are used on a local basis or during transient, difficult conditions. The contribution of lubricating oil in PAH emissions exists but was not considered an important issue, and was not discussed in the meeting. 

Kinetic modelling of transient NO reduction by CO in the presence of O2 over an automotive exhaust gas catalyst. 

Furthermore, for cost reduction, the amount of Pt used in the PEFC industry will be required to be reduced to one-tenth. In more detail, a conventional, present-day automobile is using a precious metal catalyst (Pt) in an amount of about 10 g as an exhaust gas catalyst. On the other hand, the prototypes of current fuel cell vehicles, with fuel cell stacks of about 100 kW,... 

Cerium toxicity has been previously studied in its Ce form, and, more recently, a mechanism of cerium uptake by fibroblasts was proposed. Cerium oxide is indeed used in its nanometric form as an exhaust gas catalyst, and, when the nanoparticles are diluted, they form a dispersion of individual nanoparticles. To study the impact of nanoparticles through a water path and describes the interaction between a water dispersion of nanoparticles and a model bacteria. Thill et al. selected cerium oxide as the model nanoparticles, and E. coli was chosen as a widely used model organism. They found that (1) a large amount of Ce02 NPs can be adsorbed on the E. coli outer membrane (2) the speciation of the NPs is significantly modified after adsorption (3) the adsorption of the NPs and their reduction are associated with a significant bacterial cytotoxicity and (4) the toxicity of the NPs is prevented when they are put into contact with the bacteria in the presence of the growth medium. 

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