Carbon monoxide oxidation silver oxide catalyst

Promoters are often needed in addition to the actual catalyst itself. In general promoters increase the rate of a desired reaction this can occur because of a general increase in reaction rates or because of an increase in selectivity towards one product by comparison to others. Most promoters tend to be specific to a particular reaction and catalyst but some promoters can accelerate different reactions. For example potassium (usually added as K2O) promotes the silver catalyzed ethylene oxidation to ethylene oxide (Section 2.4), and also promotes carbon monoxide hydrogenation over Fe catalysts (Section 4.8). 

Figure 6.4. The rate enhancement of catalytic reactions with catalyst potential. At left the oxidation of methane on platinum to carbon dioxide at right the oxidation of carbon monoxide on silver particles. Reprinted from C. G. Vayenas, S. Bebelis, I. V. Yentekakis, and H. G. Lintz. Catalysis Today 11, 303. Copyright (1992). With permission from Elsevier Science.

Carbon monoxide oxidation over catalysts prepared by in situ activation of amorphous gold-silver-zirconium and gold-iron-zirconium alloys, A. Baiker, M. Maciejewski, S. Taghaferri, and P. Hug, J. Catal, 1995, 151, 407. 

The most successful class of active ingredient for both oxidation and reduction is that of the noble metals silver, gold, ruthenium, rhodium, palladium, osmium, iridium, and platinum. Platinum and palladium readily oxidize carbon monoxide, all the hydrocarbons except methane, and the partially oxygenated organic compounds such as aldehydes and alcohols. Under reducing conditions, platinum can convert NO to N2 and to NH3. Platinum and palladium are used in small quantities as promoters for less active base metal oxide catalysts. Platinum is also a candidate for simultaneous oxidation and reduction when the oxidant/re-ductant ratio is within 1% of stoichiometry. The other four elements of the platinum family are in short supply. Ruthenium produces the least NH3 concentration in NO reduction in comparison with other catalysts, but it forms volatile toxic oxides. 

Ethylene is selectively oxidized to ethylene oxide using a silver-based catalyst in a fixed-bed reactor. Ethylene and oxygen are supplied from the gas phase and ethylene oxide is removed by it. The catalyst is stationary. Undesired, kinetically determined by-products include carbon monoxide and water. Ideally, a pure reactant is converted to one product with no by-products. 

Cuesta A, Lopez N, Gutierrez C. 2003. Electrolyte electroreflectance study of carbon monoxide adsorption on polycrystalline silver and gold electrodes. Electrochim Acta 48 2949-2956. Date M, Hamta M. 2001. Moisture effect on CO oxidation over Au/Ti02 catalyst. J Catal 201 221-224. 

The use of equation (3.2) to study the behaviour of catalysts is known as solid electrolyte potentiometry (SEP). Wagner38 was the first to put forward the idea of using SEP to study catalysts under working conditions. Vayenas and Saltsburg were the first to apply the technique to the fundamental study of a catalytic reaction for the case of the oxidation of sulfur dioxide.39 Since then the technique has been widely used, with particular success in the study of periodic and oscillatory phenomena for such reactions as the oxidation of carbon monoxide on platinum, hydrogen on nickel, ethylene on platinum and propylene oxide on silver. 

In a separate investigation MargeHs and Roginekii1107 carried nut catalytic oxidation of ethylene at 350° over vanadium pentoxidc. reportedly similar to metallic silver in catalytic properties. TVv asoertainod that carbon dioxide was formed faster from, ethylene oxide, or from acetaldehyde under comparable conditions, than from ethylene itself. Further, they noted the formation of carbon monoxide, and determined that its rate of formation was considerably greater than that of carbon dioxide, increasing still more in the presence of adtk-d ethylene oxide. The addition of ethylene oxide also appeared to depro both ethylene oxide and acetaldehyde formation. They concluded that reactions leading to carbon dioxide and water did not proceed by wav of ethylene oxide, but by way of some other intermediates, and tlmt-this process could occur either on the catalyst surface or in the gas phase. 

Rival Kinetic Models in the Oxidation of Carbon Monoxide over a Silver Catalyst by the Transient Response Method... 

The oxidation of carbon monoxide by nitrous oxide and oxygen over a silver catalyst at 20°C was analysed by both the Hougen -Watson procedure and the transient response method. The rival models derived from both procedures were clearly distinguished by the mode of the transient response curves of C02 or N caused by the concentration jump of CO, 02 or N20. 

Let us associate the graph R in Fig. 1.7 with the mechanism of oxidation of nitrogen oxides by carbon monoxide over a silver catalyst (41). The reaction proceeds along two stoichiometrically independent routes ... 

Introduction.—The oxidative dehydrogenation of alcohols to aldehydes and ketones over various catalysts, including copper and particularly silver, is a well-established industrial process. The conversion of methanol to formaldehyde over silver catalysts is the most common process, with reaction at 750—900 K under conditions of excess methanol and at high oxygen conversion selectivities are in the region 80—95%. Isopropanol and isobutanol are also oxidized commercially in a similar manner. By-products from these reactions include carbon dioxide, carbon monoxide, hydrogen, carboxylic acids, alkenes, and alkanes. 

Heterogeneous catalysis is activated when the catalyst slides against itself or other materials, e.g. ceramics. Oxidation reactions of hydrogen, carbon monoxide and methane were demonstrated as being enhanced by rubbing platinum, palladium and silver, respectively [29-31], and the reduction of carbon dioxide is enhanced by the rubbing of iron oxide [32],... 

These results are to be contrasted with tho.se obtained with solid catalysts such as copper, copper oxide, silver oxide, barium peroxide, platinum oxide, and active charcoal in which only very small amounts of hydrogen and carbon monoxide were obtained. From the fact that rather high yields of oxygenated compounds could also be obtained with the gaseous catalyst, it would seem that decomposition of these compounds played ail important part in the production of the hydrogen and carbon monoxide. 

Catalytic reductions have been carried out under an extremely wide range of reaction conditions. Temperatures of 20 C to over 300 C have been described. Pressures from atmospheric to several thousand pounds have been used. Catal3rsts have included nickel, copper, cobalt, chromium, iron, tin, silver, platinum, palladium, rhodium, molybdenum, tungsten, titanium and many others. They have been used as free metals, in finely divided form for enhanced activity, or as compounds (such as oxides or sulfides). Catalysts have been used singly and in combination, also on carriers, such as alumina, magnesia, carbon, silica, pumice, clays, earths, barium sulfate, etc., or in unsupported form. Reactions have been carried out with organic solvents, without solvents, and in water dispersion. Finally, various additives, such as sodium acetate, sodium hydroxide, sulfuric acid, ammonia, carbon monoxide, and others, have been used for special purposes. It is obvious that conditions must be varied from case to case to obtain optimum economics, yield, and quality. 

Methylisocyanate Chemistry. The chemistry involved in manufacturing methylisocyanate, the largest volume monoisocyanate, is phosgena-tion of monomethylamine to yield carbamoyl chloride. The carbamoyl chloride is then decomposed to methylisocyanate and hydrochloric acid. Methylamine can also be reacted directly with carbon monoxide to give N-methylformamide. N-methylformamide can be oxidized with pure oxygen in the presence of a silver catalyst to yield methylisocyanate. 

---