Reaction preferential oxidation

A further purification step is carried out through the CO preferential oxidation reaction, generally employing precious metal-based catalysts, mostly Pt [10-13]. 

O Connell, M, Kolb, G, Schelhaas, KP, Schuerer, J, Tiemann, D, Ziogas, A, Elessel, V. The development and evaluation of micro-structured reactors for the water-gas shift and preferential oxidation reactions in the 5 kW range. Int. J. Hydrog. Energy 2010 35 2317-2327. 

Both the preferential oxidation reaction and the hydrogen oxidation taking place in parallel are highly exothermic, which can lead to local overheating of fixed catalyst beds [59]. The CO in the reformate needs to be reduced to levels below 100 ppm, which are regarded as acceptable for state-of-the-art reformate-tolerant polymer electrolyte membrane fuel cells (PEMFCs). 

Bimetallic catalysts, mostly combinations of platinum with other metals such as tin [331] and rhodium [324], are promising candidates for the preferential oxidation reaction. Platinum/tin oxide catalysts showed significant reaction rates even at 0 °C [214]. Similar with platinum/rhodium catalysts, an alloy is formed from both metals, which changes the properties of both source metals [214]. Other additive metals, which may improve the activity and selectivity of platinum catalysts, may well be ruthenium and cobalt [329]. 

The kinetics of the preferential oxidation reaction of carbon monoxide (PrOx), for the hydrogen oxidation reaction (H2OX) and for the reverse water-gas shift reaction (RWGS) were provided, which had been determined in the relevant parameter space [398] ... 

Figure 5.49 Effect of the S/C ratio (here expressed as R = S/2C) on the hydrogen yield of an ethanol fuel processor at different operating temperatures, Tref, of the reformer operating temperature of water-gas shift 200°C selectivity of preferential oxidation reaction 90% [440].

The steam reformer was operated at 280 °C, while the preferential oxidation reaction was performed at 180 °C [589]. A vacuum insulation and high infrared reflective gold coating minimised heat losses from the system. The latter was required because the glass had high infrared emissivity. The fuel processor was 22-mm wide, 21-mm long and 10.7-mm thick. It was tested in connection with a miniaturised fuel cell [590]. It achieved 98% methanol conversion. About 2.5 W of electric energy were produced. 

Laguna, Oil, Hemdndez, W.Y., Arzamendi, G., Gandia, L.M., Centeno, MA., and Odriozola, JA. (2014) Gold supported on CuO /CeOj catalyst for the purification of hydrogen by the CO preferential oxidation reaction (PROX). Euel, 118,176 185. 

The production of copper from sulphide minerals is accomplished with a preliminary partial roast of die sulphides before reaction widr air in the liquid state, known as mattes, to form copper metal (conversion). The principal sources of copper are minerals such as chalcopyrite, CuFeSa and bornite CuaFeSa, and hence the conversion process must accomplish the preferential oxidation of non, in the form of FeO, before the copper metal appears. As mentioned before, tire FeO-SiOa liquid system is practically Raoultian, and so it is relatively easy to calculate the amount of iron oxidation which can be canned out to form this liquid slag as a function of the FeO/SiOa ratio before copper oxidation occurs. The liquid slag has a maximum mole fraction of FeO at the matte blowing temperatures of about 0.3, at solid silica saturation. 

A microchannel reactor for CO preferential oxidation was developed. The reactor was consisted of microchannel patterned stainless steel plates which were coated by R11/AI2O3 catalyst. The reactor completely removed 1% CO contained in the Ha-rich reformed gas and controlled CO outlet concentration less than Ippm at 130 200°C and 50,000h. However, CH4 was produced from 180"C and CO selectivity was about 50%. For high performance of present PrOx reactor, reaction temperature should be carefully and uniformly controlled to reach high CO conversion and selectivity, and low CH4 production. It seems that the present microchaimel reactor is promising as a CO removal reactor for PEMFC systems. 

Zeohte Y modified with R-l,3-dithiane-1-oxide/ S-2-phenyl-l,3-dithianeoxide Total conversion of R- and S-butan-2-ol Relative ratio of preferential enantiomeric reaction of R- and S-butan-2-ol... 

Steel making, broadly speaking, is an oxidation process in which impurities such as carbon, silicon, manganese, phosphorus and sulfur present in the pig iron are removed to specified levels. It can be anticipated from the Ellingham diagram that at about 1600 °C, the elements C, Si, and Mn would oxidize preferentially before iron undergoes excessive oxidation. The oxidation reactions may be represented by... 

The initial oxidation of the flavanol components of fresh leaf to quinone structures through the mediation of tea polyphenol oxidase is the essential driving force in the production of black tea. While each of the catechins is oxidizable by this route, epigallocatechin and its galloyl ester are preferentially oxidized.68 Subsequent reactions of the flavonoid substances are largely nonenzymic. 

Oxidation reactions occur on several sites of the acid and alcohol moieties, depending on the chemical structures. For example, the trans methyl of the isobutenyl group in chrysanthemates is preferentially oxidized over the cis methyl group in rats, and the 4 -position of the phenoxy ring is oxidized to a larger extent as compared with other positions [8] (Fig. 1). 

Would the preferential CO oxidation reaction be needed if the proton-exchange membrane fuel cell (PEMFC) with Pt anode catalyst were able to work at temperatures higher than about 403 K ... 

Depending on the reason for converting the produced gas from biomass gasification into synthesis gas, for applications requiring different H2/CO ratios, the reformed gas may be ducted to the water-gas shift (WGS, Reaction 4) and preferential oxidation (PROX, Reaction 5) unit to obtain the H2 purity required for fuel cells, or directly to applications requiring a H2/CO ratio close to 2, i.e., the production of dimethyl ether (DME), methanol, Fischer-Tropsch (F-T) Diesel (Reaction 6) (Fig. 7.6). 

The ideal systems for these media are those which do not require any additional solvent, and in which the substrate is more soluble than the product, leading to preferential rejection of the product from the catalyst phase. For fluorous reactions, this would include oxidation reactions where oxygenated products are typically more polar than the substrates. In ionic liquids it is products less polar than the substrates that will normally be less soluble, although the ability to tune the structure of ionic liquids to match a particular application must... 

Oxidation of Se(0) is unlikely to involve Se isotope fractionation. Se(0) is extremely insoluble and elemental Se precipitates are often found in moderately reducing environments. As solid Se(0) is consumed by an oxidation reaction, any kinetic isotope effect is ultimately negated by mass balance effects. For example, if a strong kinetic isotope effect preferentially removes lighter isotopes from the surface of the solid, the surface becomes enriched in heavier isotopes. Ultimately, the removal of successive layers from the solid requires 100% oxidation of the Se(0) and thus there is no opportunity for any kinetic isotope effect to be expressed. 

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