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Oxidative steam reforming (OSR) of methane is investigated under exhaust gas reforming conditions in a wallcoated catalytic microchannel reactor. The process is run over different combinations of Pt-and Rh-based catalysts, namely 0.2% (by weightIn each combination, coated catalysts are locked on the opposite walls of a rectangular microchannel to face each other. Parametric study is conducted in order to observe the effects of feed compositions (molar steam-to-carbon (H 2 O/C) and oxygen-to-carbon (O 2 /C) ratios) and temperature on methane conversion and on product distribution. The results show that methane conversion is enhanced with the increase in temperature and in the amounts of O 2 and H 2 O in the feed stream. When the temperature is raised from 600 to 700 °C, methane conversion is found to improve by ca. 25% in all catalyst configurations. Increasing H 2 O/C and O 2 /C ratios improved methane conversion at most by 7% and by 23%, respectively. H 2 production also increased with temperature, with the highest increase of 5% is observed over the 2%Rh/Al 2 O 3 −2%Rh/Al 2 O 3 combination. Higher O 2 /C ratios improved the extent of methane total oxidation but decreased H 2 production. The catalyst combination involving 2% Rh/Al 2 O 3 coated oppositely onto the inner walls of the microchannel is found to exhibit the best performance in terms of methane conversion and H 2 and CO amounts in the product stream. A 10% increase in methane conversion is observed either by changing the Pt content from 0.2% to 2% or by replacing 2%Pt with 2%Rh. The results show that Rh is superior to Pt in terms of oxidation and steam reforming activities.

Mechanisms for catalytic H 2 −D 2 exchange involving subsurface hydrogen, H′ (D′), have been analyzed to predict the ranges of reaction conditions over which the reaction orders, n H 2 and n D 2 , can be used to distinguish among the various possible mechanisms. Four different mechanisms and combinations thereof have been considered: a Langmuir−Hinshelwood (LH) model, a breakthrough model invoking direct reaction between surface H(D) and subsurface H′ (D′), and two models invoking activation of H (D) by H′ (D′). In parallel, the kinetics of H 2 −D 2 exchange have been measured over 90 Ag x Pd 1−x alloy film samples with a continuous range of compositions: x = 0 → 1. For conditions with P H 2 ≫ P D 2 , the reaction orders are found to be n H 2 ≅ 0 and n D 2 ≅ 1. The value of n H 2 ≅ 0 is inconsistent with an LH mechanism under conditions with a hydrogen coverage of θ ≅ 1. A mechanism in which two subsurface H′ (D′) atoms promote recombinative desorption of H (D) atoms on the surface is consistent with the observed reaction orders under conditions in which the coverages on the surface and in the subsurface are θ ≅ 1 and θ′ ≈ 0, respectively.

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