The superior performance of CoMnOx catalyst with ball-flowerlike structure for low-temperature selective catalytic reduction of NOx by NH3

Preparation of Mesoporous Mn–Ce–Ti–O Aerogels by a One-Pot Sol–Gel Method for Selective Catalytic Reduction of NO with NH3

“…The decrease of the total H 2 consumption beyond 600 • C can be caused by the growth of crystallite size due to sintering and the decrease of the number of available reducible species. As the total H 2 consumption of the MCTO-600 exhibited the largest of 1.80 mmol g −1 , therefore, its low-temperature NH 3 -SCR activity was the highest among the four samples, indicating that the reducibility of active species favored the improvement of the NH 3 -SCR activity [14,18,38]. It has been generally confirmed that the adsorption and activation of NH3 on the acid sites of the catalyst surface is a key step in the NH3-SCR, so the NH3-TPD test was used to study the number and the strength distribution of acid sites over the catalysts.…”

“…This difference could be caused by sintering and motion of primary nanoparticles in calcination, which caused different accessibilities for X-rays for different samples. It has been proved that Mn 4+ species and their redox cycle can accelerate the conversion of NO to NO 2 , thereby enhancing the low-temperature NH 3 -SCR performance via the "fast-SCR" path (2NH 3 [18], which displays a reaction rate 10 times higher than that of the standard SCR process [42]. The proportion of Ce 3+ /Ce and absolute Ce 3+ content on the surface of the MCTO-600 reached 24.0% and 0.41%, respectively, which were the highest among the four catalysts investigated.…”

“…Ce 3+ could generate a charge imbalance to form oxygen vacancies and unsaturated chemical bonds on the surface of the catalysts and promote the migration of oxygen from the bulk to the surface, thus accelerating the oxidation of NO to NO 2 to facilitate the SCR reaction [22,23]. It has been widely reported that O α species are more active than O β species due to their higher mobility, and a high O α /(O α + O β ) ratio favors the oxidation of NO to NO 2 in NH 3 -SCR to enhance the low-temperature activity of the catalyst [18,43]. It is noted that the percentage of O α species was the highest for the MCTO-400 among the catalysts, which may be due to the smallest crystallite sizes at the lowest calcination temperature.…”

“…The NH 3 -SCR process on the MCTO-600 catalyst follows both the Eley-Rideal (E-R) mechanism and the Langmuir-Hinshelwood (L-H) mechanism.In addition, the V-based catalysts have some inevitable disadvantages, such as the toxicity of VO x , a narrow operating temperature window (300-400 • C), and a low N 2 selectivity [6,14,15]. Therefore, it is of great practical importance to develop catalysts with high catalytic activity and good SO 2 resistance under low-temperature conditions (<200 • C).The MnO x -based catalysts have been considered as promising candidates for NO removal by the NH 3 -SCR method owing to their inherent environmentally benign nature and superior catalytic activity [13][14][15][16][17][18][19][20][21]. As an additive, CeO 2 can further enhance the catalytic activity of MnO x in the low temperature range because of its unique oxygen storage capacity and redox performance [22,23].…”

“…The MnO x -based catalysts have been considered as promising candidates for NO removal by the NH 3 -SCR method owing to their inherent environmentally benign nature and superior catalytic activity [13][14][15][16][17][18][19][20][21]. As an additive, CeO 2 can further enhance the catalytic activity of MnO x in the low temperature range because of its unique oxygen storage capacity and redox performance [22,23].…”