Selective catalytic reduction of NOx by methane over Co/ZrO2 catalysts

The effect of the preparation on the catalytic performances of Co/ZrO2 cata lysts in the selective catalytic reduction of nitrogen oxides with methane was studied. The samples were prepared by grafting and impregnation with di fferent solutions of cobalt salts. X-ray photoelectron spectroscopy analysi s showed that the cobalt oxidation state is 2+ in all samples. It was found that a high cobalt dispersion favours nitrogen selectivity, especially at temperatures below 350 degreesC. All samples show a maximum NO conversion i n the temperature interval 300-350 degreesC, but the nitrogen selectivity d ecrease at this temperature range. The Fourier transform infrared spectrosc opic studies showed that although the surface nitrates formed on bare zirco nia are highly inert, the nitrates on cobalt particles fully interact with methane at 300 degreesC to produce an organic nitrogen-containing deposit t hat is known to react with NOx to form nitrogen. Compared with the referenc e Co-ZSM-5 catalyst, the nitrates on Co/ZrO2 samples react with methane at a higher temperature, which accounts for their catalytic performances. Copy right (C) 2001 John Wiley & Sons, Ltd.