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Selective catalytic reduction (SCR) of NO x with NH 3 has been widely used for the removal of NO x. Because of the inevitable disadvantages of conventional V 2 O 5 -WO 3 (MoO 3)/TiO 2 catalysts such as poor low-temperature SCR activity and toxicity of vanadium, as well as the high-cost and over-strong NH 3 adsorption of zeolite catalysts, the development of efficient and non-toxic metal oxide SCR catalysts is highly demanded. Previously, we have developed an environmentally-benign CeO 2 -SiO 2 mixed-oxide SCR catalyst (CeSi 2), which exhibited superior SO 2 resistance ability. However, the low-temperature SCR activity on CeSi 2 was not that satisfactory. In this work, we proposed a new strategy of Mo doping to improve the low-temperature SCR activity on CeSi 2 , which was very crucial for its practical application. By a simple co-precipitation method, a homogenous Mo-Ce-Si mixed-oxide catalyst was prepared. The Mo doping could significantly enhance the NH 3 -SCR activity on CeSi 2 below 250 °C, and the optimal catalyst was Mo 0.1 CeSi 2 , which could achieve 80% NO x conversion at 200 °C. Mo 0.1 CeSi 2 also exhibited superior N 2 selectivity and resistance to SO 2 /H 2 O poisoning. Via a series of characterizations, it was found that the redox properties and surface acidity on CeSi 2 by Mo doping, which accounted for the enhanced low-temperature NH 3 -SCR activity on Mo 0.1 CeSi 2. The reaction mechanism on Mo 0.1 CeSi 2 was also fully revealed by in situ DRIFTS experiments. This work provided a new insight for the development of efficient low-temperature SCR catalysts with superior SO 2 resistance ability. [Display omitted] • A homogeneous Mo-Ce-Si mixed-oxide catalyst was prepared. • Enhanced low-temperature NH 3 -SCR activity was achieved on Mo doped CeO 2 -SiO 2. • Mo-Ce-Si catalyst exhibited excellent resistance to SO 2 poisoning. • Surface acidity and redox properties of CeO 2 -SiO 2 were promoted by Mo doping. • NH 3 -SCR reaction on Mo-Ce-Si catalyst proceeds through E-R mechanism. [ABSTRACT FROM AUTHOR]

Understanding the nature of active sites on metal oxide catalysts in the selective catalytic reduction (SCR) of NO by NH 3 (NH 3 -SCR) is a crucial prerequisite for the development of novel efficient NH 3 -SCR catalysts. In this work, two CeO 2 -based SCR catalyst systems with diverse acidic metal oxides-CeO 2 interfaces, i.e., Nb 2 O 5 -CeO 2 (Nb 2 O 5 /CeO 2 and CeO 2 /Nb 2 O 5) and WO 3 -CeO 2 (WO 3 /CeO 2 and CeO 2 /WO 3), were prepared and used to reveal the relationship between NH 3 -SCR activity and surface acidity/redox properties. In combination with the results of the NH 3 -SCR activity test and various characterizations, it was found that the NH 3 -SCR performance of Nb 2 O 5 -CeO 2 and WO 3 -CeO 2 catalysts was highly dependent on the strong interactions between the redox component (CeO 2) and acidic component (Nb 2 O 5 or WO 3), as well as the amount of paired redox-acid sites. From a quantitative perspective, an activity-surface acidity/redox property relationship was proposed. For both Nb 2 O 5 -CeO 2 and WO 3 -CeO 2 catalysts systems operated at the more concerned low-temperature range (200 °C), the NH 3 -SCR activity in low NO x conversion region (< 40%) was mainly dominated by the surface acidity of catalysts, while the NH 3 -SCR activity in high NO x conversion region (> 40%) was more determined by redox properties. [Display omitted] • Nb 2 O 5 -CeO 2 and WO 3 -CeO 2 catalysts with tuned redox-acid property were synthesized. • Paired redox-acid sites formed through strong interaction between Nb 2 O 5 /WO 3 and CeO 2. • NH 3 -SCR activity was well controlled by the paired redox-acid sites. • Surface acidity and redox property were investigated from a quantitative perspective. • A clear surface acidity/redox property-activity relationship was established. [ABSTRACT FROM AUTHOR]

Modifying CeO 2 with acid sites is a common strategy for designing efficient catalysts for the selective catalytic reduction of NO x by NH 3 (NH 3 -SCR of NO x). However, the effect of acid metal oxide modification on the SO 2 resistance of CeO 2 has not been well revealed. In this work, it was found that the SO 2 resistance of CeO 2 modified with several acid metal oxides (i.e. , MoO 3 , WO 3 and Nb 2 O 5), followed an order of Mo/CeO 2 ≥ W/CeO 2 > Nb/CeO 2. Further systematic characterizations revealed that Mo-OH and W-OH on CeO 2 as Brønsted acid sites could better inhibit the SO 2 adsorption and the sulfation of active sites than highly dispersed NbO x mainly as Lewis acid sites because NH 4 + coordinated to Brønsted acid sites could help trap SO 2 to form ammonium sulfates rather than metal sulfates. The findings in this work provided important guidance for the design of efficient catalysts with superior SO 2 resistance performance. [Display omitted] • CeO 2 modified with varying acid metal oxides showed different resistance to SO 2. • Highly dispersed MoO 3 or WO 3 could better shield CeO 2 from SO 2 poisoning than Nb 2 O 5. • Mo and W sites as Brønsted acid sites could better inhibit the SO 2 adsorption on CeO 2. • SO 2 could interact with both highly dispersed Nb 2 O 5 and CeO 2 on Nb/CeO 2. • A strategy for designing efficient catalysts with superior resistance to SO 2 was provided. [ABSTRACT FROM AUTHOR]