Collecting spatially resolved gas phase concentration profiles in catalytic monoliths by applying suction probe techniques has become an important tool for understanding the reaction sequence and for optimizing the design of structured catalysts. The impact of the capillary on the data is investigated by means of computational fluid dynamics (CFD) simulations using the exemplary cases of catalytic partial oxidation of methane over rhodium and oxidation of carbon monoxide over palladium. The influence of a suction probe inside a rectangular channel of a monolith on flow field and concentration profiles are discussed. Four different configurations were investigated: probe in center or corner of the channel with insertion from upstream or downstream in each case. If the capillary is located in the corner of the channel, the influence on the data is negligible. For a position in the center, a noticeable impact was observed. A simple analytical model can predict the reduction of the mass flux due to the insertion of the probe. The worst case exhibits a reduction >50 %. The measuring error is dependent on the direction of insertion of the capillary into the channel (upstream or downstream). Additionally, axial diffusion plays a significant role. For any interpretation of the data, the influence of the probe on the measured data has to be considered. The quantification of the error requires threedimensional CFD simulations.
Abstract:The catalytic partial oxidation (CPOX) of several hydrocarbon mixtures, containing n-dodecane (DD), 1,2,4-trimethylbenzene (TMB), and benzothiophene (BT) as a sulfur compound was studied over a Rh/Al 2 O 3 honeycomb catalyst. The in-situ sampling technique SpaciPro was used in this study to investigate the complex reaction system which consisted of total and partial oxidation, steam reforming, and the water gas shift reaction. The mixtures of 83 vol % DD, 17 vol % TMB with and without addition of the sulfur compound BT, as well as the pure hydrocarbons were studied at a molar C/O-ratio of 0.75. The spatially resolved concentration and temperature profiles inside a central channel of the catalyst revealed three reaction zones: an oxidation zone, an oxy-reforming zone, and a reforming zone. Hydrogen formation starts in the oxy-reforming zone, not directly at the catalyst inlet, contrary to methane CPOX on Rh. In the reforming zone, in which steam reforming is the predominant reaction, even small amounts of sulfur (10 mg S in 1 kg fuel) block active sites.
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