Poisons thermal stability

PH3 is an extremely poisonous, highly reactive, colourless gas which has a faint garlic odour at concentrations above about 2 ppm by volume. It is intermediate in thermal stability between NH3 (p. 421) and ASH3 (p. 557). Several convenient routes are available for its preparation ... 

Mercury (Quicksilver, Hydrargyrum), Hg, at wt 200.61, silvery liq, mp —38.87°, bp 356.9°, d 13.546g/cc at 20°. Insol in w, HC1, ale and eth sol In nitric acid. Sometimes found native poisonous. Can be prepd by heating the ore cinnabar (HgS) either in air or with lime. Forms numerous salts, some of which are very expl, eg, Hg fulminate, Hg azide, etc. The presence of Hg in expls, even in minute quants, is unde-sireable because it affects the result of thermal stability tests. Marshall (Ref 1) describes various tests used in Engl and Ger for its detection in different expls and propints Refs 1) Marshall 2, 708-12(1917) 2) Mellor... 

Thus, if the incorporation of some metal oxides indicated a notable improvement in the catalytic activity (permitting it to operate at lower reaction temperatures),the incorporation of metals, especially Pt and working in the presence of H2, has prolonged the hfe of the catalysts. However, new catalyst formulations have recently increased the resistance of these catalysts to such poisons as water or sulfur during the isomerization of n-C5 and n-C6 paraffins. Nevertheless, the use of other anions, by supporting WO3 or MoOf or heteropolyacids,which have higher thermal stability, can also be interesting alternative routes to develop new catalytic systems. 

Thermal Stability. Lithium-ion batteries can be poisoned by water, and so materials going into the cell are typically dried at 80 °C under vacuum. Under these conditions, the separator must not shrink significantly and definitely must not wrinkle. Each battery manufacturer has specific drying procedures. The requirement of less than 5% shrinkage after 60 min at 90 °C (in a vacuum) in both MD and TD direction is a reasonable generalization. 

Alberti et al. investigated the influence of relative humidity on proton conductivity and the thermal stability of Nafion 117 and compared their results with data they obtained for sulfonated poly(ether ether ketone) membranes over the broad, high temperature range 80—160 °C and RHs from 35 to 100%. The authors constructed a special cell used in conjunction with an impedance analyzer for this purpose. Data were collected at high temperatures within the context of reducing Pt catalyst CO poison-... 

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. 

To conclude this section, it is necessary to state that Pd and Pd-based membranes are currently the membranes with the highest hydrogen permeability and selectivity. However, the cost, availability, their mechanical and thermal stabilities, poisoning, and carbon deposition problems have made the large-scale industrial application of these dense metal membranes difficult, even when prepared in a composite configuration [26,29,33-37],... 

Electronic promoters, for example, the alkali oxides, enhance the specific activity ofiron-alnmina catalysts. However, they rednce the inner snrface or lower the thermal stability and the resistance to oxygen-containing catalyst poisons. Promoter oxides that are rednced to the metal during the activation process, and form an alloy with the iron, are a special group in which cobalt is an example that is in industrial use. Oxygen-containing compounds such as H2O, CO, CO2, and O2 only temporarily poison the iron catalysts in low concentrations. Sulfur, phosphorus, arsenic, and chlorine compounds poison the catalyst permanently. 

In order to suggest an efficient catalyst system for automotive emission control, Pd-W03 and Pd-La203 catalysts were characterized before and after thermal aging and phosphorous contact, li was found that deactivation of Pd-W03 involves severe metal vaporization during ihermal aging. On the other hand, Pd-La203 has exceptional thermal stability while it is poisoned by 1-5 wi. phosphorous,... 

It is the polynuclear aromatic system and the heteroatom species that pose the greatest limitation to resid conversion. The polynuclear aromatic and heteroatom species 1) have high thermal stability 2) poison catalysts by deposition of heteroatoms and metals and 3) readily form coke that deposits on the catalyst and detracts from liquid production. 

Two different cerium oxide promoted zirconias were prepared and tested as supports for Pd catalysts for the catalytic oxidation of methane, alone and in presence of a strong catalyst poison (SO2). The introduction of cerium oxide was carried out by incipient wetness of zirconium hydroxide or zirconium oxide, followed by calcination. Both catalysts present very different properties, the first method producing a catalyst with better performance, and thermal stability markedly higher than the unmodified zirconia support. However, the addition of cerium does not lead to any enhancement of the catalyst performance in presence ofSC>2,... 

On the other hand, cerium has been shown to be an effective oxygen reservoir, enhancing the activity of many oxidation catalysts. Due to this property, cerium oxide is also considered to potentially enhance the thioresistance of the catatysts. This aspect is of great practical importance, since the use of palladium catalysts is hindered by the poisonous effect of sulphur compoimds, often present in off gases. Most works dealing with ceria-zirconia catalysts have been carried out with catalysts prepared by coprecipitation methods, whereas in this work an ahemative procedure, based on the incipient wetness technique is used to incorporate ceria to the zirconia support. The aim is to maintain the advantages of zirconia supports, especially the thermal stability. 

Since the discovery by three groups working independently that Cu-ZSM-5 catalyses the catalytic reduction of NO by various hydrocarbons, much research has been carried out with this material [234]. However, these catalysts present major problems in terms of their thermal stabilities and sensitivities to water [5]. Another important system that is also being studied intensively is Pt/Al203, and generally Pt on different metal oxide supports [6], since this is already used in conventional (stoichiometric) exhaust gas cleanup and has proven stability and tolerance to typical potential poisons in the engine exhaust. Other systems such as Co-ZSM-5, Ga-ZSM-5, Cu-Zr02 and H-ZSM-5 have been found to be active [7], but their industrial application has not been achieved yet. 

In addition, catalysts must have high thermal stability to resist sintering, particularly where there is a need for periodic regeneration by combustion of coke deposited on the catalyst. A further desirable characteristic is the ability to resist deactivating influence of poisons, notaby sulfur compounds, which are often present in reactant streams. 

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. 

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