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Synthesis

Mining waste displays catalytic prowess

Simple process turns toxic red mud from aluminum processing into an active catalyst for generating hydrogen from ammonia

by Mitch Jacoby
September 5, 2016 | APPEARED IN VOLUME 94, ISSUE 35

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Credit: Alper Uzun
Abundant and hazardous, red mud (background) can serve a useful function: converting ammonia (left) to hydrogen and nitrogen (right).
Credit: Alper Uzun
Abundant and hazardous, red mud (background) can serve a useful function: converting ammonia (left) to hydrogen and nitrogen (right).

In a laboratory demonstration of the old adage “one man’s trash is another man’s treasure,” researchers in Turkey have shown that red mud, a hazardous by-product of aluminum processing, can be converted simply and inexpensively to a catalyst that liberates hydrogen from ammonia (Sci. Rep. 2016, DOI: 10.1038/srep32279). The finding might lead to a more practical way to safely store and generate enough hydrogen for fuel-cell vehicles to enable long-distance driving between refueling stops. Red mud is the highly alkaline sludge formed by sodium hydroxide digestion of bauxite ore. Known as the Bayer process, this bit of caustic chemistry, which is the main method for extracting aluminum from the ore, globally generates more than 100 million metric tons of the mud per year, which remains rich in iron and other heavy metals. Samira Fatma Kurtoğlu and Alper Uzun of Koç University report that treating the sludge with hydrochloric acid and exposing it to ammonia at 700 °C converts iron in the material to a catalytically active iron nitride species, ɛ-Fe2N. Tests show that the treated mud decomposes NH3 to H2 and N2 nearly as well as costly ruthenium catalysts, which are often used for this application, and better than any other non-precious-metal catalyst.

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