| Hydrogen-fed fuel cells represent a superior design for portable power applications due to their high efficiency, high energy density and negligible pollution issues. However, the on-board storage of hydrogen is unsafe and inefficient, and thus production of hydrogen from a liquid fuel in a microreformer would be more desirable [1]. Among the fuels considered, methanol is considered an excellent choice since it is sulfur free and can be reformed at a low temperature (200-250°C) [2]. The low reforming temperature could be a significant advantage since the fuel processor heat recovery will be easier to manage and the required insulation around the processor will be minimized. Also, the low reforming temperature results in low CO concentration in the reformate. This will eliminate the need for a CO clean up reactor, hence, decreasing the weight and volume of the fuel processor. Clearly, the fuel reformer is a critical component since it could greatly affect the gravimetric and volumetric density of the overall fuel cell system [3]. Therefore, reducing the weight and volume of the fuel reformer is a critical engineering issue that involves: (1) Isothermal reactor. (2) Highly active and selective catalyst.; In this study, two reactor configurations will be considered, a micro packed-bed reactor and a wall-coated reactor. The catalyst that shows the highest activity at low temperature is the CuO/ZnO/Al2O3 catalyst, which is also the catalyst used for methanol synthesis and low temperature water gas shift [4]. Cu based catalysts, however, have the disadvantages of fast deactivation, poor thermal stability above 270°C and pyrophoric characteristics. Pd/ZnO have been shown to be a promising catalyst for MSR [5]. Iwasa et al. reported that Pd when supported on ZnO and reduced at temperatures higher than 300°C shows a high activity and selectivity to CO2 and H2 [6]. The high selectivity was attribute to PdZn alloy formation [7].; For the reactor design portion of this study, it is concluded that isothermal operation in a micro packed-bed reactor would require 300mum inner diameter. A wall-coated reactor on the other hand was found to be free from any transport limitations. Thick catalyst coats, up to 100mum, are shown to increase the reformer's volumetric productivity. It is concluded that a multi-channel wall-coated reformer is a better design since the pressure drop would be be minimized compared to 300mum i.d. packed-bed.; For the catalyst design part of this study, the Pd/ZnO catalyst activity and selectivity are shown to be independent from extent of PdZn alloy formation, in contrast to what have been reported in the literature [6, 8]. Particle size was found to have the largest effect on Pd/ZnO catalyst selectivity. On the other hand, methanol conversion was not affected by particle size, which suggested that ZnO might have a role in MSR. MSR reactivity experiments with PdZn/AL2O3 after removal of ZnO were performed. The results showed that PdZn without ZnO has a lower selectivity and lower activity for MSR, which confirms that ZnO is an essential phase in MSR catalyst.; In the future we plan to investigate the role of ZnO in MSR by performing in-situ infrared spectroscopy. Also, in-situ EXAFS would help reveal the structure of the active phase for MSR. |
