Revealing the Excellent Low-Temperature Activity of the Fe_1–xCe_xO_δ-S Catalyst for NH₃-SCR: Improvement of the Lattice Oxygen Mobility

Abstract

The development of selective catalytic reduction catalysts by NH3(NH3-SCR) with excellent low-temperature activity and a wide temperature window is highly demanded but is still very challenging for the elimination of NO x emission from vehicle exhaust. Herein, a series of sulfated modified iron–cerium composite oxide Fe1–x Ce x Oδ-S catalysts were synthesized. Among them, the Fe0.79Ce0.21Oδ-S catalyst achieved the highest NO x conversion of more than 80% at temperatures of 175–375 °C under a gas hourly space velocity of 100000 h–1. Sulfation formed a large amount of sulfate on the surface of the catalyst and provided rich Brønsted acid sites, thus enhancing its NH3 adsorption capacity and improving the overall NO x conversion efficiency. The introduction of Ce is the main determining factor in regulating the low-temperature activity of the catalyst by modulating its redox ability. Further investigation found that there is a strong interaction between Fe and Ce, which changed the electron density around the Fe ions in the Fe0.79Ce0.21Oδ-S catalyst. This weakened the strength of the Fe–O bond and improved the lattice oxygen mobility of the catalyst. During the reaction, the iron–cerium composite oxide catalyst showed higher surface lattice oxygen activity and a faster replenishment rate of bulk lattice oxygen. This significantly improved the adsorption and activation of NO x species and the activation of NH3 species on the catalyst surface, thus leading to the superior low-temperature activity of the catalyst.

Lattice Oxygen Activation Triggered by Ultrasonic Shock Significantly Improves NO Selective Catalytic Reduction

“…Thus, the two high temperature peaks at regions of 350–400 and 500–600 °C can be ascribed to reduction of surface lattice oxygen and bulk lattice oxygen, respectively . It is obvious that after ultrasonic treatment, the profile of α-Fe 2 O 3 exhibited a significant shift to lower temperature, verifying the great promotion of lattice oxygen diffusion due to generation of bulk defects . Meanwhile, according to the quantitative analysis results in Table S2, UT-Fe 2 O 3 shows a hydrogen consumption that is smaller than that of P-Fe 2 O 3 , which can be reasonably attributed to the partial loss of lattice oxygen.…”

“…Nevertheless, one notable issue exhibited by these methods is that they typically suffer from entangled modulation of surface chemisorbed oxygen and bulk lattice oxygen, which brings significant difficulty in approaching the explicit contribution from lattice oxygen. ,,, Meanwhile, for some chemical reactions requiring multiple active sites, such as NH 3 selective catalytic reduction of NO (NH 3 –SCR), the case becomes much more complex. As is well-known, both acidity and redox properties are indispensable for promoting NH 3 –SCR reaction. , In most cases, it is hard to modify redox feature without bringing about an impact on surface acidity. − This adds extra difficulty in understanding the role of lattice oxygen activation in modulating catalytic performance. Therefore, the precise regulation of oxygen species, particularly the sole modulation of lattice oxygen without additional disruption of surface chemisorbed oxygen species, is urgently needed but still a formidable challenge.…”

Iron-Based Catalysts with Oxygen Vacancies Obtained by Facile Pyrolysis for Selective Hydrogenation of Nitrobenzene

“…Combining the results of XPS (Figure g) and EPR (Figure S4), due to the presence of sufficient oxygen vacancies, hydrogen first dissociated at the oxygen vacancies, generating atomic hydrogen, which then overflowed to the surface of the iron oxide. The reduction ability of atomic hydrogen was significantly higher than that of hydrogen molecules, which made the reduction peak appear at a significantly lower temperature. , The oxygen vacancies in catalyst Fe@C-2 enabled an increase in the hydrogen adsorption energy, while greatly reducing the energy barrier associated with hydrogen bond breaking, − which promoted the dissociation and activation of H 2 , resulting in the catalytic performance of catalyst Fe@C-2 being superior to that of the other catalysts.…”

Facet-Dependent Oxygen Mobility and Reaction Pathways for Oxidative Dehydrogenation of 1-Butene over Bi2MoO6

“…Oxygen mobility has been regarded as the decisive factor for 1-butene ODH. 29 The consumption, 42,43 replenishment, 44,45 and migration 46 of lattice oxygen involved in the oxygen mobility process display its unique functions in diverse redox reactions. In this section, a series of experimental and theoretical measurements are O involves the consumption of lattice 16 O, the subsequent replenishment of gaseous 18 O 2 , and the final consumption of lattice 18 O.…”