Catalytic ammonia oxidation, heat transfer

Instabilities in beds of porous catalysts, for strongly exothermic processes, occur when heat transfer rates from the bed are not adequate, so the temperature rises, increasing reaction rates, and thus producing heat energy. This instability produces hot spots inside the bed and melts or inactivates the catalyst. Besides other solutions, our microcapillary catalytic reactor elements, using very thin porous layers of a catalyst (6-10 pm), attached to the heat-transferring body (glassy carbon), ensure stable exothermal processes, as the ammonia synthesis, or CO oxidation to CO2. 

The catalytic oxidation of ammonia is one of the rare cases where a non-porous solid catalyst is used. To calculate the ammonia conversion and the temperature of the wire we have to recall the equations for the interaction of external mass and heat transfer and a chemical reaction derived in Section 4.5.3. Initially, we consider the ammonia oxidation on a single Pt wire for cross-flow of the gas. 

Similar tests of the fiuidized-bed method have been successful with a variety of molecular adsorbates and catalysts (other zeolites, supported oxides, naphthalene, pyridine, methanol, alkanes, alkenes, acetonitrile, ammonia, etc.) (25). We believe that this fiuidized-bed method is a major step forward for measurements of working catalysts with UV Raman spectroscopy. It should also be a useful method for measurements of catalytic kinetics by reducing heat and mass transfer effects that arise when catalysts are used in the form of pellets. In the limit of low conversions... 

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