Fast Catalytic Reactions Research Articles

Diffusive catalytic combustion

Catalytic combustion at temperatures down to about 580K is used in commercial heating applications. In this paper the role of the catalyst in diffusive catalytic combustion is discussed for methane and propane as fuels with platinum catalysts. Problems of modelling are discussed for the diffusive-convective flow between catalyst particles and for the diffusion-reaction balance on the active surface. For these catalysts, it is concluded that the Thiele modulus for the reaction is high, the effectiveness factor for the catalyst is low and the reaction is thus diffusion-controlled. These conclusions are supported by experimental results which show for methane that the diffusive-convective flow in the gas between the catalyst particles is barely affected by the very fast catalytic reaction occurring on the surface. Experiment also suggests that cracking of the methane is an important feature of the process. It is suggested that cracking may have two important influences on the combustion: (i) as a source of hydrogen to sensitise the methane oxidation and (ii) as a source of carbon which, in effect, acts as a poison for the catalytic process. A similar picture is provided by the catalytic combustion of propane. Limitations to the potential of catalytic combustion in its present state of development are discussed.