Surface structure sensitivity of manganese oxides for low-temperature selective catalytic reduction of NO with NH3

TLDR: In this article, the results of the catalytic tests revealed that both K-Hol and H-Hol with almost same catalytic activities had much higher reaction rates than β-MnO2 under the same conditions, and even at a high gas hourly space velocity of 160,000h−1, KHol obtained more than 90% conversions of NO in a wide temperature window of 100-300°C.

Abstract: Hollandite-type manganese oxides with K+ or H+ cations in the tunnels (K-Hol or H-Hol) were successfully synthesized and investigated in low-temperature selective catalytic reduction of NO by NH3. The results of the catalytic tests revealed that both K-Hol and H-Hol with almost same catalytic activities had much higher reaction rates than β-MnO2 under the same conditions, and even at a high gas hourly space velocity of 160,000 h−1, K-Hol obtained more than 90% conversions of NO in a wide temperature window of 100–300 °C. The high resolution transmission electron microscopy observations showed that both K-Hol and β-MnO2 were tetragonal prism-shaped nanorods with same exposed {1 1 0} planes, and the atoms in the {1 1 0} planes of K-Hol arranged to form semitunnel structures, while the {1 1 0} planes of β-MnO2 were relatively smooth surfaces. The temperature-programmed reduction by H2 and thermal gravimetric analyses indicated that active surface lattice oxygen atoms of K-Hol were around 1.6% with respect to total lattice oxygen atoms. The transition reactions of NH3 demonstrated that K-Hol with special semitunnel structured surface and active surface lattice oxygen showed much stronger ability to efficiently adsorb and activate NH3 molecules than β-MnO2. Hence, both efficient semitunnel structured external surfaces and high active surface lattice oxygen atoms predominantly accounted for the high catalytic activities.