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The deployment of fuel cell electric vehicles is constrained by the paucity of hydrogen fueling stations and price, which is dominated by the costs of hydrogen storage and transportation. With more hydrogen per volume than liquid H2 and an extensive distribution infrastructure in place, ammonia is a promising vector for efficient hydrogen distribution. In this talk we describe the development of innovative catalytic membrane reactor (CMR) technology for the delivery of high purity H2 from ammonia cracking.
The CMR integrates state-of-the art catalysts with thin metal membranes in an innovative design. Conventionally, the catalyst is supplied to CMRs in the form of a packed bed either in the interior of the support or in the annulus surrounding the membrane. In our design a dense palladium membrane a few microns in thickness is formed by electroless deposition on an asymmetric ceramic support. The catalyst is impregnated within the mesoporous layer adjacent to the membrane, and excellent dispersion maximizes its activity. The use of alkali promoters is found to further enhance the kinetics.
The intimate proximity of the catalyst to the hydrogen permeable membrane provides a number of advantages over conventional systems. Radial transport limitations are mitigated, dramatically enhancing H2 recovery. Ammonia decomposition is inhibited by H2, but the efficient removal of H2 in the CMR enables temperature reductions by up to 200 ºC and decreases catalyst loading requirements by a factor of 3. Similar improvements in volumetric productivity over leading reports are obtained, reducing footprint requirements. We have developed a detailed axisymmetric model that captures the reactor performance with high fidelity, and this is used for the analysis and design of these systems.