III International Conference

PP-II-99surface of metallic substrates was pre-coated with a thin (~ microns) protective low- porouslayer of corundum or zirconia by the unique technology of blast dusting [2]. Activecomponents including both mixed oxides and platinum are supported by successiveimpregnation with appropriate suspensions or solutions followed by drying and calcination.The monolith catalysts were tested in a tubular stainless-steel reactor. The axialtemperature along the monolith was scanned at selected points by thermocouples located inthe central channel. The contact time was varied in the range of 0.2-0.02 s. The feedcomposition was CH 4 (natural gas) - 22-29 vol.%, air – balance. Gas composition wasanalyzed by mass-spectrometric and GC methods.The consumption of methane and oxygen and axial profile of catalyst temperature duringstart-up and steady-state reaction were found to be determined by the inlet gas temperature,contact time, thermal conductivity of substrates. For both catalysts based on corundum andmetallic supports, the scan of the axial monolith temperature along the catalyst during start-upshows that ignition starts in the central or rear zone of a monolith depending on a contacttime. After ignition, a zone of the maximal catalyst temperature moves towards the monolithentrance until the stationary state is attained. The time required to attain the steady state isshorter for metallic monolith catalysts as compared to ceramic ones and decreases at shortercontact times. Hence, the high thermal conductivity of metallic monolith provides fasteffective transfer of heat generated in a zone of exothermic combustion along the monolithinto its rear part where endothermic reforming reactions occur. Such peculiarities of metallicbasedmonolith catalysts are especially important for mobile fuel processors which mustensure a rapid start-up.For the stationary state, at long contact times, a zone of the maximal temperature locatesat the inlet part of monolith and, at decreasing contact time, it shifts to the rear part ofmonolith due to its cooling by incoming gas. In addition, for shorter contact times, thetemperature gradient along the monolith declines due to contribution of the direct POMreaction having mild exothermicity as well as hindering of endothermic reformingreactions.Therefore, the monolith catalysts of different types were shown to be very efficientand stable in the POM at short contact times and temperatures up to 1200 °C. They insure ahigh conversion of methane and high concentration of syngas in a wide range of contact timesand at high gas velocities.References1. C. Song, Catal.Today 77 (2002) 17.2. V.A. Sadykov, S.N. Pavlova et al. Kinetics and Catalysis, Vol. 46, No. 2 ( 2005) 227.344