Excellent activity and selectivity of Pd/ZSM-5 catalyst in the selective catalytic reduction of NOx by H2

Superior de-NOx activity and N2 selectivity of the Pd/ZSM-5 catalyst was observed at low temperature (<200 degrees C) for the selective catalytic reduction of NOx by H2 (H2-SCR). Various Pd/ZSM-5 catalysts were prepared by calcinating at different temperatures (e.g., 500 degrees C, 650 degrees C, 750 degrees C, and 850 degrees C) and treated at reductive conditions before the H2-SCR reaction was performed. Among the prepared catalysts, the one prepared at the calcination temperature at 750 degrees C resulted in 96.7% NOx conversion and 96.8% N2 selectivity at 150 degrees C. Based on the H2-O2 reaction, the higher activity of the Pd/ZSM-5 catalyst calcined at 750 degrees C was attributed to its superior H2 activation ability for the H2-SCR reaction. The combined X-ray diffraction (XRD), temperature-programmed hydride decomposition (TPHD), and transmission electron microscopy (TEM) results revealed that highly dispersed Pd particles were generated on the catalyst calcined at 750 degrees C, while large Pd agglomerates were formed on the one calcined at 500 degrees C. It can be concluded that the catalytic activity of Pd/ZSM-5 improves by optimizing the calcination temperature, resulting in high Pd dispersion. Moreover, the Pd catalyst calcined at 750 degrees C showed high resistance to CO, maintaining >94% NOx conversion at 175 degrees C under 1000 ppm CO in the feed gas. Therefore, the catalyst calcined at 750 degrees C can be potentially used for industrial applications because of its simple preparation method and high resistance to CO.