Southwest Catalysis Society (swcs)

Distributed hydrogen for the hydrogen economy will require new catalysts and processes. Existing large scale hydrocarbon steam reforming plants can not simply be reduced in size to meet the size, economic, safety, and frequent duty cycle requirements for applications for fuel cells, hydrogen fueling stations, and industrial uses such as hydrogenation reactions, gas turbine cooling, metal processing, etc. Consequently, there is a need to completely reassess how hydrogen can be made for the emerging hydrogen economy. Unlike the catalytic processes in the chemical and petroleum industries that operate at steady state conditions hydrocarbons reformers integrated to fuel cells must operate in a transient mode to follow the power load demand. As the power requirements rapidly change so must the rate of hydrogen delivery. Thus the process and catalyst materials must be designed for large turn-down-ratios especially with regard to space velocity and rapid transients in temperature. The nature of these operations must be factored into the catalyst and system design. A key limitation of traditional base metal (Ni, Cu, Cr, Fe, etc) reforming particulate catalysts used in the chemical industry is their inability to sustain activity and mechanical stability after frequent start and stop tests. During these operations, common for processors integrated to fuel cells, the catalyst is rapidly heated and cooled causing mechanical failure of the catalyst particulate structure. During the cooling process liquid water from the reformate stream condenses on the surface of the reduced catalyst causing it to oxidize and slowly deactivate. Reduced base metals spontaneously oxidize liberating large quantities of heat upon exposure to air generating rendering them unsafe for a consumer application such as a fuel cell. Precious metal catalysts deposited on monolithic substrates are resistant to the deactivation modes experienced by base metals. They can be used without complicated and time consuming reductions required for base metal reforming catalysts. Precious metals are sufficiently robust that they can undergo start and stop modes without loss of activity after air or liquid water exposure. They are sufficiently active that only small amounts deposited on a monolith or heat exchanger wall can be used resulting in reformers with greatly reduced size and weight, lower pressure drop, enhanced mechanical stability, and rapid response to transient operations. For this reason hydrogen fueling stations are being built utilizing precious metal monolith technology (1). In the accompany figure a catalyzed plate heat exchanger is shown. The hydrocarbon-containing process gas is being steam reformed on the process side while the heat of reaction is provided by the catalytic oxidation of fuel and air on the combustion side. This design enhances heat transfer allowing for space velocities up to 10 times higher than traditional packed bed. Catalyzed plate heat exchanger Combustion catalyst Metal plate FUEL + O2 CO2 + H2O + HEAT FUEL + O2 CO2 + H2O + HEAT Steam reforming catalyst HC + H2O + HEAT H2 + CO HC + H2O + HEAT H2 + CO Heat flow