(547a) Ni3Al Foil as a Catalyst Precursor for Methanol Decomposition

Efficient and low-cost hydrogen production from alcohols or hydrocarbons is a very important part of fuel cell technologies [1]. Microreactors are highly promising for this process because of high surface to volume ratio and high rates of mass and heat transfer compared with conventional reactors [2]. One of the key issues is to develop efficient and inexpensive heterogeneous catalysts. The catalysts are usually coated on microchannel-structured metal sheets in the microreactors by a complex process [3]. Ni₃Al is known to be an excellent high-temperature structural material [4]. Its brittleness at ambient conditions, as with many other intermetallic compounds, used to be a serious problem. We have overcome this problem by directional solidification [5] and have succeeded in cold-rolling this compound into thin foils 23 mm in thickness [6]. Recently, we also found that intermetallic compound Ni₃Al powder showed high catalytic activity and selectivity for methanol decomposition (CH₃OH ® 2H₂ + CO) after alkali-leaching treatment [7]. These results suggest a possibility of the Ni₃Al foils to be used both as catalysts and as structural sheets in the microreactors. However, the catalytic properties of the Ni₃Al foils have not been investigated, yet. In this study, we examined the catalytic properties of cold-rolled Ni₃Al thin foils for the methanol decomposition in the temperature range of 633-793 K. It was found that the methanol decomposition was effectively catalyzed over the Ni₃Al foils in the temperature range of 713-793 K. The catalytic activity rapidly increased during the initial several hours of reaction at 793 K, and then stabilized at a high value (about 98% of methanol conversion) during the subsequent reaction. Furthermore, the Ni₃Al foils showed almost no loss of activity through the whole range of reaction time, displaying an excellent catalytic stability. Surface analyses by BET, SEM, XRD, and TEM revealed that porous structure of carbon nanofibers containing fine Ni particles were formed on the Ni₃Al foils during the reaction at 793 K. These surface products, i.e., fine Ni particles and carbon nanofibers, are supposed to serve as a catalyst and a catalyst support for the methanol decomposition, respectively. The results demonstrate that the Ni₃Al foils can be used both as catalyst precursors and as structural materials of microreactors for hydrogen production.

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