Catalytic Combustion of Light Hydrocarbons under Fuel-Rich Conditions

Introduction The integration of fuel processors, the catalytic units that can convert fossil fuels to hydrogen-rich streams, with hydrogen fuel cells is considered as a promising solution to the problems related to the availability, distribution and storage of hydrogen. Recent computer-based studies have demonstrated the possibility of efficient hydrogen production on-board the vehicles through catalytic indirect partial oxidation (total oxidation followed by steam reforming) of propane, a major constituent of LPG [1]. The model catalyst was bimetallic and included Pt (specific for exothermic total oxidation) and Ni (specific for endothermic hydrogen producing steam reforming) metals over the same support in order to drive micro level energy exchange between the reactions, leading to elevated amounts of hydrogen produced. In this work, total oxidation of propane and n-butane (second major hydrocarbon in LPG) are investigated under fuel-rich conditions, i.e. at a set of fuel:oxygen ratios above the stoichiometric values, which can be found from the following reactions as 0.20 for propane and 0.15 for n-butane: C3H8 + 5O2 = 3CO2 + 4H2O n-C4H10 + 6.5O2 = 4CO2 + 5H2O Supported monometallic Pt/Al2O3 and Ni/Al2O3 prepared by incipient-to-wetness impregnation technique and bimetallic Pt-Ni/Al2O3 prepared by sequential impregnation technique are the catalysts of interest. The metal contents are 0.2 per cent (by weight) Pt and 15 per cent Ni. The catalytic activities are monitored through a series of reaction tests conducted in a continuous flow fixed-bed microreactor system equipped with mass flow and temperature controllers. Pretreatment of the catalysts at 500C for 4h under 20 ml/min hydrogen flow is followed by reaction at temperatures increasing from 150C to 385C at a rate of 1C/min. Inlet composition is set as HC:O2:N2 (ml/min)=1:x:139-x and total inlet flow is kept constant at 140 ml/min with x depending on the fuel:oxygen ratio. Product analysis is conducted through two gas chromatographs equipped with Porapak Q and Molecular Sieve 5A columns for hydrocarbon and fixed gas analysis, respectively. The catalyst samples are characterized by electron microscopy studies using a Philips XL30 ESEM-FEG system.