Lead oxide catalysts

For this reaction, our aim was to improve the known catalytic action of iron oxides to an extent that the high activity of the generally used platinum catalyst would be equalled. Together with Ch. Beck, the author finally found iron oxide-bismuth oxide combinations, and iron oxide-manganese oxide-bismuth oxide combinations which were outstanding catalysts. An iron oxide-lead oxide catalyst proved to be less satisfactory (44). 

It has been found that lead oxide catalysts supported on basic carriers such as MgO or B -AloOj exhibit excellent activity and selectivity for the oxidative coupling of methane. Lattice oxygen is proved to be responsible for the formation of C hydrocarbon. 

The use of lead oxide (PbO) for the conversion of ethyl carbamate (EC) to form diethyl carbonate (DEC) using ethanol has been reported this reaction is the second step in the conversion of urea to DEC by alcoholysis (Scheme 22.15). Of interest is that the catalytic species appears to be a mixture of metallic Pb and PbOj, generated under the reactions conditions from the initially added PbO by reaction with ethanol to generate ethane, acetaldehyde, carbon dioxide and water. This lead oxide catalyst exhibited excellent activity in comparison other metals and high conversion yield (16%), and could be reused up to five times without significant loss in activity. ... 

From the above observations it was concluded that basic solids are more appropriate catalysts than acidic materials. This fundamental assumption was confirmed by the selectivity of the various alkaline earth oxides (see Table 3). Basicity increases from top to bottom along with the selectivity however, the selectivities obtained in the best case are not much better than for the lead oxide catalyst. From Tanabe s [9] work it is well known that surface basicity increases by impregnating such oxides with alkali anions. When using such materials as catalysts, selectivity is increased (see Table 4) this may be considered as a very convincing proof that basicity is a very important feature of successful catalysts. It was fiirther shown that the amount of... 

Lead sesquioxide is used as an oxidation catalyst for carbon monoxide ia exhaust gases (44,45) (see Exhaust control), as a catalyst for the preparation of lactams (46) (see Antibiotics, P-lactams), ia the manufacture of high purity diamonds (47) (see Carbon, diamond-natural), ia fireproofing compositions for poly(ethylene terephthalate) plastics (48), ia radiation detectors for x-rays and nuclear particles (49), and ia vulcanization accelerators for neoprene mbber (50). 

In the other market areas, lead naphthenates are used on a limited basis in extreme pressure additives for lubricating oils and greases. Sodium and potassium naphthenates are used in emulsiftable oils, where they have the advantage over fatty acid soaps of having improved disinfectant properties. Catalyst uses include cobalt naphthenate as a cross-linking catalyst in adhesives (52) and manganese naphthenate as an oxidation catalyst (35). Metal naphthenates are also being used in the hydroconversion of heavy petroleum fractions (53,54) and bitumens (55). 

Salts of neodecanoic acid have been used in the preparation of supported catalysts, such as silver neodecanoate for the preparation of ethylene oxide catalysts (119), and the nickel soap in the preparation of a hydrogenation catalyst (120). Metal neodecanoates, such as magnesium, lead, calcium, and zinc, are used to improve the adherence of plasticized poly(vinyl butyral) sheet to safety glass in car windshields (121). Platinum complexes using neodecanoic acid have been studied for antitumor activity (122). Neodecanoic acid and its esters are used in cosmetics as emoUients, emulsifiers, and solubilizers (77,123,124). Zinc or copper salts of neoacids are used as preservatives for wood (125). 

Either gas- or hquid-phase reactions of ethyleneamines with glycols in the presence of several different metal oxide catalysts leads to predominandy cychc ethyleneamine products (13). At temperatures exceeding 400°C, in the vapor phase, pyrazine [290-37-9] formation is favored (14). Ethyleneamines beating 2-hydroxyalkyl substituents can undergo a similar reaction (15). 

A number of process improvements have been described, and iaclude the use of white mineral oil having a boiling range of 300—400°C (60) or the use of a mixture of cresols (61). These materials act to reduce the reaction mixture s viscosity, thus improving mixing. Higher sebacic acid yields are claimed by the use of catalysts such as barium salts (62), cadmium salts (63), lead oxide, and salts (64). 

Cobalt. Without a doubt cobalt 2-ethyIhexanoate [136-52-7] is the most important and most widely used drying metal soap. Cobalt is primarily an oxidation catalyst and as such acts as a surface or top drier. Cobalt is a transition metal which can exist in two valence states. Although it has a red-violet color, when used at the proper concentration it contributes very Httie color to clear varnishes or white pigmented systems. Used alone, it may have a tendency to cause surface wrinkling therefore, to provide uniform drying, cobalt is generally used in combination with other metals, such as manganese, zirconium, lead, calcium, and combinations of these metals. 

The mechanism of poisoning automobile exhaust catalysts has been identified (71). Upon combustion in the cylinder tetraethyllead (TEL) produces lead oxide which would accumulate in the combustion chamber except that ethylene dibromide [106-93-4] or other similar haUde compounds were added to the gasoline along with TEL to form volatile lead haUde compounds. Thus lead deposits in the cylinder and on the spark plugs are minimized. Volatile lead hahdes (bromides or chlorides) would then exit the combustion chamber, and such volatile compounds would diffuse to catalyst surfaces by the same mechanisms as do carbon monoxide compounds. When adsorbed on the precious metal catalyst site, lead haUde renders the catalytic site inactive. 

An effect which is frequently encountered in oxide catalysts is that of promoters on the activity. An example of this is the small addition of lidrium oxide, Li20 which promotes, or increases, the catalytic activity of dre alkaline earth oxide BaO. Although little is known about the exact role of lithium on the surface structure of BaO, it would seem plausible that this effect is due to the introduction of more oxygen vacancies on the surface. This effect is well known in the chemistry of solid oxides. For example, the addition of lithium oxide to nickel oxide, in which a solid solution is formed, causes an increase in the concentration of dre major point defect which is the Ni + ion. Since the valency of dre cation in dre alkaline earth oxides can only take the value two the incorporation of lithium oxide in solid solution can only lead to oxygen vacaircy formation. Schematic equations for the two processes are... 

Lead and compounds Manganese and compounds SPA Lead oxide Tetraethyl lead (TEL) Batteries Explosives and pyrotechnics Paint Pesticides Petrochemicals Printing Refineries Vehicle exhausts Batteries Catalyst Glass Paint Pyrotechnics... 

All of the Au/metal oxide catalysts deactivate quickly, under the conditions shown in Figure 4. In addition, the deactivation of the Au/metal oxide catalysts appears to be enhanced in the presence of COj. In support of the theory that increased basicity of the metal oxides leads to lower stability, we carried out COj temperature programmed desorption experiments on the various catalysts. The COj TPD data also confirmed that an increase in the basicity of the metal oxides leads to an increase in the amount of COj adsorption on the catalysts. 

Photoreduction of Si02 doped by six valance molybdenum results in decrease of the surface concentration of Mo ions and, as a consequence, reduces the capability of the sample to emit 2. However, such a treatment does not lead to a complete suppression of emission capability because, according to [96], illumination reduces only 30% of Mo ions in molybdenum oxide catalysts deposited on Si02. 

Generally radical acceptors or oxidation catalysts, which effectively remove free radicals formed during milling and mixing procedures. Inter-macromolecular action leads to reduction of the entanglements between polymer molecules. Chemically activated zinc soaps. 

The oxidation catalyst should not be oversized. Otherwise, too much N02 is produced at intermediate temperatures and this will lead to a decrease of the reaction rate of the SCR reaction due to the low rate of the N02-SCR reaction. A way out of the problem would be a kind of controlled oxidation catalyst producing 50% NOz over the entire temperature range [43],... 

Ammonia oxidation catalysts (sometimes called slip catalyst) are conventional oxidation catalysts based on precious metals. The most active types are based on Pt. Then-activity is strongly dependent on the temperature and, thus, relatively large catalyst volumes are required for the ammonia oxidation below 250°C. At rising temperatures, their oxidation power increases and this leads to the formation of N20 and NO. Especially undesired is their strong tendency to form N20 at intermediate temperatures (250-300°C) [2] if the gas coming from the SCR catalyst also contains unreacted NO, which allows for the reaction ... 

A catalytic system Mo-V-Nb-W supported on alumina was prepared by impregnation and investigated for the selective oxidation of propane. The effects of the variation of each metal and of the catalyst preparation were analysed. The results show that Mo and V species supported on alumina can lead to catalysts with high selectivity to propene and reasonable selectivity to acrolein. The presence of Nb and W seems to have little effect. The catalyst can be affected by the method of impregnation. 

The intercalated catalysts can often be regarded as biomimetic oxidation catalysts. The intercalation of cationic metal complexes in the interlamellar space of clays often leads to increased catalytic activity and selectivity, due to the limited orientations by which the molecules are forced to accommodate themselves between sheets. The clays have electrostatic fields in their interlayer therefore, the intercalated metal complexes are more positively charged. Such complexes may show different behavior. For example, cationic Rh complexes catalyze the regioselective hydrogenation of carbonyl groups, whereas neutral complexes are not active.149 Cis-Alkenes are hydrogenated preferentially on bipyridyl-Pd(II) acetate intercalated in montmorillonite.150 The same catalyst was also used for the reduction of nitrobenzene.151... 

A large batch exploded violently (without flame) during vacuum distillation at 90-100°C/20-25 mbar. Since the distilled product contained up to 12% butyroni-trile, it was assumed that the the oxime had undergone the Beckman rearrangement to butyramide and then dehydrated to the nitrile. The release of water into a system at 120°C would generate excessive steam pressure which the process vessel could not withstand. The rearrangement may have been catalysed by metallic impurities [1]. This hypothesis was confirmed in a detailed study, which identified lead oxide and rust as active catalysts for the rearrangement and dehydration reactions [2],... 

The gallium modified zeolites were activated by two successive reduction-oxidation cycles, respectively with hydrogen and air, which, according to the literature [3], lead the catalyst to its most active form. 

The hydrogen-bonding interactions within the complexes W2CI4-(y-OR)2(OR)2(ROH)2 and V Cli y-OR)2(ORT)2(Rf0H)2 may provide the molecular analogues with which to model the structure and reactivities of transition metal oxide catalysts that possess surface hydroxyl groups. The thermal treatment which is often carried out in the pretreatment of metal oxides (leading to the loss of -OH... 

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