Poisoning sulfur

4 Urea and Urea Deposit Related Catalyst Deactivation 

in the form of an aqueous solution, is used as the source of NH3 for NOx reduction in automotive diesel emission control systems. The solution is injected in front of the SCR component as line droplets, which vaporize and are mixed with 

To minimize urea solution droplets reaching the SCR catalyst, a mixing device is added between the urea injector and the SCR component to further break down the droplets and to facilitate the vaporization process. Engine cahbrations to quickly raise exhaust temperature and thereafter maintain it above a set point are also critical for the SCR catalyst to achieve and maintain high NOx reduction efficiency. With all these advanced engineering approaches, SCR catalyst deactivation caused by urea and urea-related deposits is usually less of a concern. 

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Conditions of hydrogenation also determine the composition of the product. The rate of reaction is increased by increases in temperature, pressure, agitation, and catalyst concentration. Selectivity is increased by increasing temperature and negatively affected by increases in pressure, agitation, and catalyst. Double-bond isomerization is enhanced by a temperature increase but decreased with increasing pressure, agitation, and catalyst. Trans isomers may also be favored by use of reused (deactivated) catalyst or sulfur-poisoned catalyst. 

In contrast to heterogeneous metal catalysts, the chlororhodium complex is not sensitive to sulfur poisoning,thus allowing the saturation of double bonds in the presence of mercapto functions. 

Figure 8.3.1 is a typical process diagram for tlie production of ammonia by steam reforming. Tlie first step in tlie preparation of tlie synthesis gas is desulfurization of the hydrocarbon feed. Tliis is necessary because sulfur poisons tlie nickel catalyst (albeit reversibly) in tlie reformers, even at very low concentrations. Steam reforming of hydrocarbon feedstock is carried out in tlie priiiiiiry and secondary reformers. 

Sulphinol sulpholane, water, di-2-propanolamine sulpholane will decompose and give sulfur poisoning... 

These tests demonstrated that the Lurgi Rectisol process provides an extremely pure synthesis gas which can be charged directly to the metha-nation plant without problems of sulfur poisoning of the nickel catalyst. However, in order to cope with a sudden sulfur breakthrough from Rectisol as a result of maloperation, a commercial methanation plant should be operated with a ZnO emergency catchpot on line. 

The space velocity was varied from 2539 to 9130 scf/hr ft3 catalyst. Carbon monoxide and ethane were at equilibrium conversion at all space velocities however, some carbon dioxide breakthrough was noticed at the higher space velocities. A bed of activated carbon and zinc oxide at 149 °C reduced the sulfur content of the feed gas from about 2 ppm to less than 0.1 ppm in order to avoid catalyst deactivation by sulfur poisoning. Subsequent tests have indicated that the catalyst is equally effective for feed gases containing up to 1 mole % benzene and 0.5 ppm sulfur (5). These are the maximum concentrations of impurities that can be present in methanation section feed gases. 

Figure 9. Relative rate of CO hydrogenation as a function of copper coverage on a Ru(OOOl) catalyst Reaction temperature 575K. Results for sulfur poisoning from Figure 7 have been replotted for comparison.

These results, coupled with the chemisorption titrations, provide evidence that a new phase of palladium is formed with tin under hydrogen that is more resistant to sulfur poisoning. ... 

There are a number of informative reviews on anodes for SOFCs [1-5], providing details on processing, fabrication, characterization, and electrochemical behavior of anode materials, especially the nickel-yttria stabilized zirconia (Ni-YSZ) cermet anodes. There are also several reviews dedicated to specific topics such as oxide anode materials [6], carbon-tolerant anode materials [7-9], sulfur-tolerant anode materials [10], and the redox cycling behavior of Ni-YSZ cermet anodes [11], In this chapter, we do not attempt to offer a comprehensive survey of the literature on SOFC anode research instead, we focus primarily on some critical issues in the preparation and testing of SOFC anodes, including the processing-property relationships that are well accepted in the SOFC community as well as some apparently contradictory observations reported in the literature. We will also briefly review some recent advancement in the development of alternative anode materials for improved tolerance to sulfur poisoning and carbon deposition. 

In the following sections, the electrical conductivity, electrochemical activity toward hydrogen oxidation, and the sulfur poisoning behavior of Ni-YSZ cermet anodes will be discussed in detail, together with the effects of various processing procedures and testing conditions. 

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