The formation of the intermetallic diffusion barrier layer by the controlled in-situ oxidation method for Pd and Pd/alloy porous stainless steel composite membranes was investigated. SEM and EDS results showed the existence of an oxide layer as the intermetallic diffusion barrier for oxidation temperatures higher than 600°C. At oxidation temperatures lower than 600°C, there might still be an oxide layer at the membrane-substrate interface although it was too thin to be detected by SEM and EDS. The alloy formation study showed that annealing at 500°C under helium atmosphere did not produce alloys with uniform compositions either for Pd/Ag or Pd/Cu membranes. However, annealing at 600°C gave a uniform Pd/Cu-porous stainless steel (PSS) composite membrane, with no detectable presence of elements from the PSS substrate, further demonstrating the oxide layer as an effective intermetallic diffusion barrier.

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A mathematical steady-state modeling framework for the isothermal operation of a membrane reactor for methane steam reforming is developed, and a comparative performance assessment of the catalytic membrane reactor (CMR) versus a conventional packed bed reactor (PBR) is accordingly conducted. A detailed literature benchmarking suggests that the models developed in the present study predict total methane conversion levels within 99% of the experimental values reported in the literature. The proposed Pd-and Pd/Au-based CMR model is utilized for the aforementioned performance analysis under a broad range of reactor operating conditions such as temperature (350-750 C), pressure (2-30 bars), steam to methane ratio (1-15), membrane thickness (1-50 mm), and permeate-side sweep ratio (1-100). In all simulation runs conducted, the superior performance of both the Pd-and Pd/Aubased CMR over the PBR was amply demonstrated. Furthermore, within the proposed CMR modeling framework, an index-based analysis is conducted that concretely quantifies progress towards the attainment of key process intensification objectives. In particular, by appropriately defining the D-index, which explicitly captures potential performance and process intensification benefits associated with attainable total CH 4 conversion levels under different reactor operating conditions, it is shown that the optimum CMR performance is achieved at high pressure and low temperature operating conditions, which was particularly suitable for the attainment of key process intensification objectives as well as optimum performance target levels.

The surface interactions and associated phase changes of the annealed electroless plated Pd and Ag on porous stainless steel (PSS) supports were investigated in the temperature range of 500-800 °C. The complete miscibility of the Pd and Fe binary solid solutions was verified by the X-ray phase analysis. The Fe segregation into the Pd matrix was as high as 59 wt % upon annealing at 800 °C for 20 h in H 2 . It was further shown that the solid solutions of Fe and Ag were immiscible for the temperature range investigated. In the case of the ternary phase analysis, it was found that both the Pd/Fe and Pd/Ag alloy formations took place on the support surface, in which both alloy compositions became richer in Pd with decreasing annealing temperature.