Platinum surfaces methanation

Fig. 4.25 Arrhenius plot of methane oxidation at a platinum surface.

Noller et a/. 23-725,767,900,952 continued their investigations on the catalytic decomposition of chlorinated and brominated hydrocarbons on Ba, Ca, Mg, A1 oxides and salts studies on these and related surfaces have reported by other workers - - - - - . Decomposition of chlorinated methanes on titanium , on sodium , and on other metal surfaces have been reported by Anderson et al. similar studies on 2-bromobutane with nickel and platinum surfaces have been made by Burwell et Nutt and Carter carried out a molecular beam study of the decomposition of methyl iodide on a hot tungsten filament. 

NH3/O2 reactions should be studied at low pressures on both clean and contaminated platinum surfaces to determine whether the relative reactivities at 1100 °C are in agreement with the hypothesis. Such experiments would also help to determine whether the methane reacts wholly at the surface or not. The balance of evidence reviewed above does slightly favour the reaction of methane solely at the surface, but definitive experiments are desirable on this point. 

Figure V.l. Proposed mechanism for Ihe methane-animonia coupling catalyzed by a platinum surface...

Deng YQ, Neved TG, Ewen RJ, Honeybonme CL, Jones MG (1993) Sulfur poisoning, recovery and related phenomena over supported padadium, rhodiinn and iridium catalysts for methane oxidation. Appl Catal A 101 51-62 Ehrhardt JJ, CoUn L, Jamois D (1997) Poisoning of platinum surfaces by hexamethyldisdoxane (HMDS) application to catalytic methane sensors. Sens Actuators B 40 117-124 Firth JG, Jones A, Jones TA (1973) The principles of the detection of flammable atmospheres by catalytic devices. Combust Flame 21 303-311... 

Dupont V, Zhang SH, Williams A Experiments and simulations of methane oxidation on a platinum surface, Chem Eng Sci 56 2659—2670, 2001. 

During the reaction of the hot catalyst surface with a flammable gas the temperature of the device increases. The Platinum coil itself serves at the same time as a resistance thermometer. The resistance increase of the coil then is a direct measure for the amount of combusted gas. Usually the amount of heat that develops during combustion is small and amounts to 800 kj/mol for methane, for example [8], Therefore the sensor is connected in a bridge circuit to a second resistor which shows the same setup as the pellistor but is catalytically inactive. The bridge voltage is then controlled by the temperature difference of the two sensors (see Fig. 5.34). 

Nickel-platinum bimetallic catalysts showed higher activity during ATR than nickel and platinum catalysts blended in the same bed. It was hypothesized that nickel catalyzes SR, whereas platinum catalyzes POX and, when they are added to the same support, the heat transfer between the two sites is enhanced [59, 60]. Advanced explanations were reported by Dias and Assaf [60] in a study on ATR of methane catalyzed by Ni/y-Al203 with the addition of small amounts of Pd, Pt or Ir. An increase in methane conversion was observed, ascribed to the increase in exposed Ni surface area favored by the noble metal under the reaction conditions. 

It will be noted that on Langmuir s hypothesis the surface becomes saturated when it is covered with a unimolecular thickness of adsorbed gas. By measuring the adsorption of gases on the surface of mica and of platinum Langmuir showed that with the exception of carbon monoxide, gases such as oxygen, nitrogen and methane apparently when adsorbed to a saturation value covered the surface with a unimolecular thickness of gas. 

To date, the only shock tube apparatus equipped to study surface reactions is the KIST facility at ATK GASL in New York. The tests done so far have studied methane oxidation, CFI4 + 2O2 CO2 + 2H2O on the surface of an SCT ferrous-based reactor impregnated with platinum based catalyst. To isolate the effects of the screen and the catalyst on the reaction, three types of tests were run catalyzed screen with combustible gases,... 

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