Chromia chemical mechanisms

C -C, on platinum-silica, 30 352 chain termination bed residence time, 39 255-256 probability, CO pressure effects, 39 258 chemical mechanisms for reactions with deuterium, on chromia, 20 73-84 chemisorption, carbon atom complexes, 32 167-167, 175-176 coupling, 27 235-238 double, 27 238, 239 cracking, 39 283 cyclic, catalysis of, 20 309-311 cyclization, 28 295 degree of strain, 25 135 dehydrogenation of, 19 88, 89 deuteration of, 25 140, 141 dimerization, 20 304... 

The derivation of a mechanism for a chemical reaction is by its very nature an uncertain process, being dependent critically on the nature and extent of the experimental evidence. Mechanisms that have at their heart a surface process or processes are even more uncertain and when the constraints imposed by the manipulation of HF are also taken into account, it is not surprising that there have been relatively few mechanistic studies made of heterogeneous catalytic fluorination. However a catalytic process cannot be said to be understood fully without a mechanism based on the experimental evidence available and such studies are helpful in the design of the next generation of catalysts. In most cases the work described below involves chromia or y-alumina based catalysts that have been pretreated according to the methods described above. Studies involving C2 and Q compounds are described in turn. 

Chromia is first reduced eventually Mn-containing oxides are also reduced. According to Reaction (3.3) the surface oxide reacts with the carbon from the alloy at the scale-alloy interface to produce gaseous carbon monoxide. This specific reaction scheme was investigated in the temperature range 800—1000°C using short-term tests under various impure helium atmospheres containing low partial pressures of H2, H2O, CO, and CH4 with online chemical analysis, as shown in Fig. 3.5 [ 14,16]. Model alloys and advanced characterization methods allowed to elucidate the exact reaction mechanism [17]. 

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