The catalytic partial oxidation (CPOX) of ethanol-blended fuels is studied over rhodium/alumina coated monoliths with ethanol/iso-octane mixtures as model systems. Blends containing 5–85 vol.% ethanol are investigated, as well as the pure substances. All mixtures show a hydrogen yield of over 80% in millisecond contact times, with the highest yield for a blend with 10 vol.% ethanol. For a high ethanol concentration in the blend, generally a high by-product formation is observed already at fuel lean conditions. The product yields cannot be linearly interpolated from the yields of the pure substances. In addition, the commercial fuels 95 RON gasoline and E85 are studied, revealing similar product yields in CPOX of the commercial fuels and the corresponding ethanol/iso-octane blends. Thus, two-component mixtures can be proposed as model system for the complex compositions of commercial fuel.

Catalytic partial oxidation (CPDX) is a promising technology for reforming of liquid hydrocarbon fuels to hydrogen or synthesis gas for use in fuel cells. The addition of a certain amount of the tail gas of the fuel cell stack to the reformer inlet feed can increase overall efficiency and lead to higher H-2 and CO selectivities and reduce coke formation. The effect of carbon dioxide or steam addition (1, 5, 10, 20, and 30 vol% of the total flow) on the performance of a CPDX reformer operated with isooctane as fuel surrogate is systematically studied over a wide range of C/O feed ratios (0.72-1.79) using a Rh/alumina honeycomb catalyst. The specific impact of the coreactants H2O and CO2 on reformer behavior can be interpreted by the water gas shift (WGS) chemistry. Production of H-2 and CO2 increases with H2O addition at the expense of CO and H2O. Opposite trends are observed in case of CO2 addition. Tail gas recyding reduces formation of soot precursors up to 50% compared to the corresponding fuel feed without coreactants. However, tail-gas recycling shifts the formation of soot precursors toward lower C/O ratios.

This chapter focuses on processing the different fuels for the use in fuel cells, that is, the chemical conversion of different hydrocarbon fuels to hydrogen or hydrogen-rich synthesis gases. Aside from an overview on fuels, fuel processors, and fuel requirements from the perspective of different fuel cells, quantitative modeling and simulation approaches are presented. The models are based on the molecular chemical processes in heterogeneous fuel conversion and describe the interactions of chemical reactions on catalytic surfaces and in the gaseous fluid with mass and heat transport. Reforming of natural gas, gasoline, diesel, and ethanol are discussed.

The significance of gas-phase reactions in catalytic partial oxidation (CPOX) of isooctane at short contact times and high temperatures is studied experimentally and numerically to gain further understanding of hydrogen production by CPOX of logistic fuels for on-board applications. Special attention is given to the formation of coke precursors. CPOX of isooctane over a rhodium coated monolith with a molar inlet C/O ratio of 1.1 is used as reference case for a two-dimensional flow field description coupled with detailed surface and gas-phase reaction mechanisms. The results reveal catalyst coking and formation of coke precursors in the oxygen-free catalyst zone. Taking the product composition of the rich operated CPOX reactors (C/O = 1.0−1.6) as inlet composition, homogeneous conversion in the gas-phase is studied in the temperature range from 873 to 1173 K in a plug flow reactor. Conversion in the gas-phase is modeled by two detailed reaction mechanisms. Results show that most of the by-products and soot precursor species arise from unconverted fuel and not from additionally added hydrocarbons like ethylene. Both mechanisms well-predict all experimentally observed trends in gas-phase composition, both in axial reactor profiles and for different inlet compositions. The amount of soot precursors raises with increasing fuel feed corresponding to an increasing C/O ratio in CPOX experiments.