Design and Pilot-Scale Tests of Monolithic Catalysts for Autothermal/Steam Reforming of Natural Gas and Biofuels

Transformation of fuels (fossil fuel, biofuels) into syngas or hydrogen is one of the most important tasks of catalysis in the energy-related fields. Catalysts comprised of precious metals and/or Ni supported on complex oxides with a high lattice oxygen mobility are known to be very efficient and stable to coking in autothermal/steam reforming of a variety of fuels including oxygenates. Monolithic substrates with a good thermal conductivity are promising for providing an efficient heat transfer within the reactor to prevent emergence of hot spots/cool zones deteriorating performance. This work presents results of research aimed on design of such catalysts and characterization of their performance parameters at the pilot-scale level.

Several types of heat-conducting substrates including compressed Ni-Al foam, fechraloy foil or gauze protected by corundum layer (either segregated by controlled oxidation or supported via blast dusting) and Cr-Al-O microchannel cermets were used. Stacked flat and corrugated bands of foil were winded into the Arkhimed spiral forming triangular channels. After spark-welding of tungsten rods as electrical current inlets, such a monolithic substrate was used for evaporation of liquid fuels sprayed via a nozzle. Monolithic substrates of planar or cylindrical shapes were washcoated with a slurry of Lnx(Ce0.5Zr0.5)1-xO2-y mixed oxides (Ln = La, Pr, or Sm, x=0-0.3) prepared via Pechini route with addition of peptizers and surfactants (loading up to 10-20 wt.%). Precious metals (up to 1 wt.% of Pt, Pd, Ru), and/or Ni (up to 10 wt. %) with respect to Ln-Ce-Zr-O were supported by incipient wetness impregnation.

Monolithic catalysts were tested in a pilot tubular stainless steel reactor equipped with the electric current heated fuel/water evaporation unit and heating coils to change the catalyst temperature in the reactions of autothermal (ATR)/steam (SR) reforming of natural gas, acetone, ethanol, anisol and sunflower oil. The molar ratios of H2O/C and O2/C in the feeds were varied in the range of 1-7 and 0-0.5, respectively; the gas flow rate was up to 2 m3/h (contact times 5-70 ms) and temperature measured at the end of monolith was changed from 500 to 900 oC.

At a proper optimization of feed composition, in ATR or SR of all fuels at 600- 800 0C, for developed catalysts a stable performance without coking for days-long tests was observed. The highest yield of syngas from oxygenates (up to 80% of the sum of H2 +CO content in the converted feed) was achieved for systems with Pr-La-Ce-Zr-O complex oxide promoted by Ni and Pt, only CH4 being observed as by-product. No spallation or cracking of the active components supported on metallic substrates was revealed. In general, compressed Ni-Al foam substrates provide the highest performance due to a higher loading of active component.

Hence, pilot-scale tests of structured catalysts on heat-conducting metal/cermet substrates with supported doped ceria-zirconia complex oxides promoted by precious metals and/or Ni in the reactor equipped with an original evaporator/mixer of water and liquid biofuels revealed their high and stable performance. This provides new possibilities for transformation of a broad range of a variety of fossil and biofuels into syngas for the fuel cell application.

This work was supported by INTAS 05-1000005-7663, INTAS YSF 06-1000014-5773, SOFC 600 FP6 EC Projects and Integration project 57 of SB RAS –Belarus National Academy of Sciences.