Simultaneously Enhancing Stability and Activity of Maghemite via Site‐Specific Ti(IV) Doping for NO Emission Control

Abstract

Maghemite (γ‐Fe2O3) is an environmentally benign catalyst for selective catalytic reduction (SCR) of NO with NH3, but its poor stability and low activity hamper its application in real NO emission control. Herein, we developed a stable Ti4+ doped γ‐Fe2O3 catalyst (Ti‐γ‐Fe2O3) by site‐specific Ti4+ doping at the octahedral sites rather than tetrahedral active sites (Fe3+Td), as substantiated by synchrotron room‐temperature X‐ray diffraction (SXRD) data. In situ SXRD and thermogravimetric analysis (TG) data demonstrate that Ti4+ cations occupying part of the octahedral sites lead to enhanced thermal stability of Ti‐γ‐Fe2O3 with respect to γ‐Fe2O3, thus enabling Ti‐γ‐Fe2O3 to stably operate at 400 °C under simulated normal SCR conditions. Fe L3‐edge and O K‐edge X‐ray absorption spectra show that the high‐valence Ti4+ doping lengthens the Fe3+Td‐O bonds, and activates the lattice oxygen species, thus improving the SCR activity. This work provides a feasible strategy for designing environmentally benign Fe2O3‐based SCR catalysts with significant stability and high catalytic activity.

A Multi‐Parametric Catalyst Screening for CO2 Hydrogenation to Ethanol

“…Bulk XRD analysis confirms the presence of α‐Fe 2 O 3 (hematite) in fresh monometallic Fe catalysts with an estimated crystalline domain size of 20.2 nm (Figure S13a). However, in the presence of Rh, the Fe component was found to be stabilized in the form of γ‐Fe 2 O 3 (maghemite) [49,50] . This observation is in line with previous works reporting that doping with transition metal cations enhances the stability of γ‐Fe 2 O 3 .…”

“…However, in the presence of Rh, the Fe component was found to be stabilized in the form of γ-Fe 2 O 3 (maghemite). [49,50] This observa-…”

Promoting effect ofN2calcination onFeCeOxfor selective catalytic reduction ofNOxwithNH3

“…Calcination with N 2 enhanced the redox ability of FeCeO x catalysts. As reported, a high redox ability could always be obtained from metal doping by forming oxygen vacancies 35,36 . Thus, the difference in oxygen vacancies between Fe 9 CeO x ‐N 2 and Fe 9 CeO x ‐air should be tested.…”

“…As reported, a high redox ability could always be obtained from metal doping by forming oxygen vacancies. 35,36 Thus, the difference in oxygen vacancies between Fe 9 CeO x -N 2 and Fe 9 CeO x -air should be tested. XPS was used to characterize the surface species state of Fe 9 CeO x -N 2 and Fe 9 CeO x -air.…”

Effects of Synthesis Conditions on Rare Earth Doped Iron Oxide Catalyst for Selective Catalytic Reduction of NOx with NH3

“…Iron is a low economic cost, and non-toxic transition metal and Fe2O3-based catalysts have attracted wide attention in NH3-SCR process because of good medium-high SCR activity, satisfactory N2 selectivity, excellent thermal stability and prominent SO2-tolerant activity at high temperatures (> 300°C), but the operating temperature window of pure FeOx is narrow (Chen et al, 2018;Han et al, 2019). In recent years, many efforts have been made to develop composite catalyst systems due to the synergetic effects.…”