Temperature effect, partial oxidation

The constraint of thermodynamic equilibrium for the butene dehydrogenation reaction is effectively removed since hydrogen is converted to water by oxidation. Equilibrium yields then approach 100% over the complete temperature and partial pressure range of interest. 

Partial oxidation of methane to syngas over Ni and Co catalysts was effected by use of microwave irradiation, and compared with conventional heating [73]. Although the same conversion levels and H2/CO ratio (2.0 0.2) were observed, the temperature of the catalyst bed was much lower (200 K) when microwave irradiation was used than with conventional heating. Under both activation modes the Ni-based... 

Recently, such a temperature oscillation was also observed by Zhang et al (27,28) with nickel foils. Furthermore, Basile et al (29) used IR thermography to monitor the surface temperature of the nickel foil during the methane partial oxidation reaction by following its changes with the residence time and reactant concentration. Their results demonstrate that the surface temperature profile was strongly dependent on the catalyst composition and the tendency of nickel to be oxidized. Simulations of the kinetics (30) indicated that the effective thermal conductivity of the catalyst bed influences the hot-spot temperature. 

In combustion processes the reaction is also highly exothermic, and, combined with the high effective activation energy of combustion processes, leads to large temperature dependence. The overall reaction products can also vary (partial oxidation versus total oxidation), and this factor must also be considered when dealing with combustion processes. 

Activity Measurements. To test catalytic properties of various samples partial oxidation of methanol to formaldehyde was studied in a flow micro-reactor operating under normal atmospheric pressure (10). For each run about 0.2 g of catalyst sample was used and the activities were measured at 173 C in the absence of any diffusional effects. The feed gas consisted of 72, 2 and by volume of nitrogen, oxygen and methanol vapor respectively. Reaction products were analysed with a 10% Carbowax 20 M column (2m long) maintained at 60 C oven temperature. 

From these experiments, one can see that the direct partial oxidation of CH4 to synthesis gas over catalytic monoliths is governed by a combination of transport and luetic effects, with the transport of gas phase species governed by the catalyst geometry and flow velocity and the lanetics determined by the nature of the catalyst and the reactor temperature. Under the conditions utilized here, the direct oxidation... 

Propene to acrolein. Hildenbrand and Lintz87,88 have used solid electrolyte potentiometry to study the effect of the phase composition of a copper oxide catalyst on the selectivity and yield of acrolein during the partial oxidation of propene in the temperature range of 420-510°C. Potentiometric techniques were used to determine the catalyst oxygen activity, and hence the stable copper phase, under working conditions. Hildenbrand and Lintz used kinetic measurements to confirm that the thermodynamically stable phase had been formed (it is known that propene is totally oxidised over CuO but partially oxidised over ). 

Production of ammonia requires large quantities of hydrogen, most of which comes from the partial oxidation of hydrocarbons with water or oxygen. A simple and important example is the so-called methane-steam gas reaction, which is favorable only at very high temperatures because of the entropy effect in the formation of H2 (see Section 4-4B) ... 

In general, as discussed earlier, the chemical properties of small particles may be different from the properties of the corresponding bulk samples. An investigation of this effect in oxidation reactions was made by Tops0e et al. (237) in the study of the room temperature oxidation of Fe304 particles 40 nm in size. The Mossbauer spectra of several partially oxidized samples and that of magnetite are shown in Fig. 37, in which it can be seen that oxidation is reflected in the ratio S of octahedral to tetrahedral spectral areas (see Section III, A, 2). Specifically, the value of S for stoichiometric magnetite... 

Raman and Mossbauer studies.97 Thus the compounds are partially oxidized and should be more correctly expressed as [M(DPG)2KIs)o.2 with the nickel in a formal oxidation state of 2.20.97 The electrical conductivity in the Ni atom chain direction is 10-2 fi 1 cm-1, 105 times that of the unoxidized parent compound.97 98 The temperature dependence of the conductivity indicates that the compound is a semiconductor with AE = 0.19+0.01 eV. Table 3 indicates that changing the halide has little effect on the conductivity but that the Ni complex is more conducting than the Pd analogue. 

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