Catalytic decomposition of pyridine gas with fine particles of metallic iron formed from limonite

•An Australian natural limonite rich in α-FeOOH is employed as a catalyst.•The limonite achieves nearly complete decomposition of 100 ppmv pyridine at 500 °C.•N2 yield upon pyridine decomposition at 500 °C is greater than 80%.•The limonite shows high activity with or without H2 reduction pretreatment.•Iron nitrides may act as intermediates for the conversion of pyridine to N2.

Catalytic decomposition of 100 ppmv pyridine (C5H5N) with an Australian limonite ore, composed mainly of goethite (α-FeOOH), has been examined for hot gas cleanup with a fixed-bed quartz reactor at 300–500 °C under a large space velocity of 51,000 h−1. When α-FeOOH in the limonite is reduced with pure H2 at 500 °C, the transformation into nanoscale particles of metallic iron (α-Fe) occurs, and the catalyst achieves almost complete C5H5N decomposition in inert He at 500 °C and provides an N2 yield greater than 80% for at least 10 h. The limonite also exhibits a high catalytic activity at 500 °C, even without H2 reduction. Based on the results of N 1s X-ray photoelectron spectroscopy and temperature-programmed desorption measurements, it is probable that the limonite-catalyzed formation of N2 from pyridine proceeds through cycle mechanisms involving α-Fe and iron nitride species.

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