Features of Ignition of Mixtures of Hydrogen With Hydrocarbons (C2, C3, C5) Over Rhodium and Palladium at Pressures of 1–2 atm

It is found that the determining factor for the catalytic ignition of mixtures of hydrogen with ethane and ethylene is not only the material of the catalyst but also the chemical nature of the C2 hydrocarbon in the mixture with H2. It is shown that the limits of the catalytic ignition of the synthesis gas over metallic rhodium (Rh) are qualitatively different from the dependences for a hydrogen–hydrocarbon mixed fuel. The dependence of the lower limit of catalytic ignition on temperature has a distinct maximum, which indicates a more complex mechanism of the catalytic process than in the case of hydrogen–methane mixtures; the Arrhenius dependence of ln [H2]lim on 1/T does not hold. Therefore, the interpretation of the upper and lower limits of catalytic ignition (ULCI, LLCI) used in the literature, taking into account catalyst poisoning by CO molecules, needs to be clarified. The relatively long delay periods of the catalytic ignition of hydrogen–n-pentane mixtures (tens of seconds) and the absence of dependence of the delays on the initial temperature allow us to conclude that the catalytic ignition of hydrogen–propane/n-pentane mixtures is determined by the rate of transfer of hydrocarbon molecules to the surface of the catalytic wire. Thus, in the oxidation of hydrogen–hydrocarbon mixtures for “short” hydrocarbons, the main factor determining the catalytic ignition is the oxidation reaction of hydrogen on the catalytic surface. With an increase in the number of carbon atoms in the hydrocarbon, the factors associated with the chemical structure, i.e., the reactivity of the hydrocarbon in catalytic oxidation, begin to play a significant role; and then the rate of oxidation is determined by the rate of transfer of the hydrocarbon molecules to (or within) the catalyst surface.