Platinum surfaces temperature

Data for 2,2-dimethylpropane are plotted in Figure 7 for comparison with n-hexane and 2,2-DMB because 2,2-dimethylpropane gave the highest ion yield of the hydrocarbons studied. Little oxidation of 2,2-dimethylpropane in 60% 02 occurred until the platinum surface temperature... 

Platinum is unaffected by most organic compounds, although some compounds may catalytically decompose or become oxidised on a platinum surface at elevated temperatures, resulting in an etched appearance of the metal. Carbon and sulphur do not attack platinum at any temperature up to its melting point. Molten platinum may dissolve carbon, but the solubility of the latter in solid solution is virtually zero. 

The platinum surface is intensively covered with adsorbed CO, especially at low temperatures and high concentration of CO where the Hinshelwood mechanism may dominate... 

Figure 7.7. Temperature-programmed desorption measurements corresponding to zero-, first-, and second-order kinetics of silver from ruthenium, CO from a stepped platinum surface, and N2from rhodium, respectively (data adapted from [J.W. Niemantsverdriet,...

Platinum serves as the catalyst for the oxidation of CO and hydrocarbons. It is relatively insensitive to contamination by lead or sulfur. At high temperatures it is not known to dissolve in the washcoat, but sintering into larger particles may lead to a substantial loss of platinum surface area with dramatic consequences for the overall oxidation activity. 

Chemisorption of oxygen at Pt(lll) has been studied in detail by Ertl s group25 and the STM evidence is for complex structural features present in the temperature range 54M60K (Figure 4.14). The limitations of the Langmuir model, frequently invoked for reactions at platinum surfaces, is obvious from... 

Subsequent to the discovery of skeletal rearrangement reactions on plati-num/charcoal catalysts, the reality of platinum-only catalysis for reactions of this sort was reinforced with the observation of the isomerization of C4 and C5 aliphatic hydrocarbons over thick continuous evaporated platinum films (68,108, 24). As we have seen from the discussion of film structure in previous sections, films of this sort offer negligible access of gas to the substrate beneath. Furthermore, these reactions were often carried out under conditions where no glass, other than that covered by platinum film, was heated to reaction temperature that is, there was essentially no surface other than platinum available at reaction temperature. Studies have also been carried out (109, 110) using platinum/silica catalysts in which the silica is catalytically inert, and the reaction is undoubted confined to the platinum surface. 

Chemistry studies of alkanes on platinum surfaces under UHV conditions are limited by the very weakly bound molecularly chemisorbed state(59). The low surface temperatures required to... 

An instrument for measuring temperatures, in the rubber industry the term is usually applied to an instrument for determining the surface temperature of mill and calender rolls, moulds, etc. The instrument is usually based on thermocouples or, where higher accuracy is required, platinum resistance thermometers. Infrared (IR) techniques are now used which have the advantage of non contact but require careful calibration for the emissivity of the surface. 

The simulations are further conducted under the experimental conditions of Inada et al. (1985). In their experiments, 4.0 mm water droplets impact on a heated platinum surface at a temperature up to 420 °C. The subcooling degree... 

Glucose oxidase was first adsorbed onto the platinum surface at a controlled potential. The protein adsorption varied depending on several factors as electrode potential, glucose oxidase concentration, pH and temperature. The effects of these factors on protein adsorption were carefully investigated. 

A spark generates many radical species in the spark gap, and these can propagate radicals throughout the vessel. A platinum surface catalyzes the reaction (H2 and O2 readily dissociate on a R catalyst surface to begin the reaction), and the surface reaction then heats the R to a high temperature, where homogeneous reaction begins rapidly. 

Potentiometric techniques have been used to study autonomous reaction rate oscillations over catalysts and carbon monoxide oxidation on platinum has received a considerable amount of attention43,48,58 Possible explanations for reaction rate oscillations over platinum for carbon monoxide oxidation include, (i) strong dependence of activation energy or heat of adsorption on coverage, (ii) surface temperature oscillations, (iii) shift between multiple steady states due to adsorption or desorption of inert species, (iv) periodic oxidation or reduction of the surface. The work of Sales, Turner and Maple has indicated that the most... 

At room temperature H2 molecules striking those crystallites of a platinum surface which have the highest work function (I) decompose into atoms. If a pure platinum surface is contacted by hydrogen, crystallites I will be covered by H atoms, those with a low work function, II, by H2 molecules, because the decomposition of H2 molecules on crystallites II requires a higher energy of activation than on crystallites I. The work function of crystallites I is lowered by the polarized H atoms that of crystallites II will not be changed essentially. All effects combined, the photoelectric emission therefore increases if hydrogen is adsorbed on a pure platinum surface. 

Fig. 31. Fowler curves of platinum surface covered with copper-phthalocyanine molecules as in Fig. 30 at room temperature (I) and at low temperature (II) [according to (77a)].

As an illustration, consider the stagnation flow over a catalytic surface during an ignition event. The inlet flow is steady, but the surface temperature increases as power through the platinum-foil surface increases. At a certain temperature the catalytic ignition occurs very rapidly. The flow configuration and conditions, which are taken from Deutschmann [101], are u n — 8 cm/s, Tln = 300 K, with an inlet mixture of 3% CH4, 3% O2, and 94% N2. The inlet-to-surface separation is L = 5 cm, and the surface Pt sites are initially covered... 

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