Novel Ru−Mg−Al−O Catalyst Derived from Hydrotalcite-like Compound for NO Storage/Decomposition/Reduction

Ru-Mg-Al hydrotalcite-like anionic clay (Mg/Al/Ru) 90: 29: 1) was successfully prepared with a constant-pH coprecipitation method. Calcination of a hydrotalcite-like precursor at 600 degrees C in the air gave rise to the well-mixed oxide Ru-Mg-Al-O that possesses a good dispersion of Ru species. Ru-Mg-Al-O catalyst after suitable pretreatment exhibits quite high NOx storage capability in the temperature range of 250-400 degrees C, and the highest NOx storage capability of about 220 mu mol g(-1) is obtained at 350 degrees C with flowing 790 ppm NO and 8% O-2 in N-2 stream. Meanwhile, the decomposition of 25-60% NO to N-2 as well as N2O is clearly observed on the catalyst at 300-400 degrees C. In situ diffuse reflectance Fourier transform ( DRIFT) spectra indicate that NOx is adsorbed and stored on a catalyst mainly in the form of various coordinated nitrites/ nitrates. On the basis of the NOx adsorption-desorption profiles as well as the in situ DRIFTS spectra, we have proposed a schematic outline for NOx storage and NO decomposition. Finally, the reduction of stored NOx species on the catalyst by H-2 was carried out at 350 degrees C, indicating that all adsorbed NOx species can be readily reduced by hydrogen.