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[Display omitted] • Hierarchical ordered MnFe 1-δ Co δ O x ternary oxide catalysts were prepared. • Co doping can enhance the low-temperature performance of the NH 3 -SCR reaction. • The enhanced performance depends on the increased acidity and redox of Hierc-MnFe 1-δ Co δ O x. • Co doping can retard the sulfuration rates of Hierc-MnFe 1-δ Co δ O x catalysts. Manganese (Mn)-based mixed oxides are considered the most efficient catalysts for low-temperature ammonia selective catalytic reduction of nitrogen oxides (NO x) (NH 3 -SCR of NO x). Water resistance and sulfur tolerance, especially the SO 2 tolerance of Mn-based catalysts, are the main obstacles preventing their practical application. Therefore, in this study, a series of cobalt (Co)-doped MnFeO x ternary mixed oxides catalysts with a hierarchically ordered structure (Hierc-MnFe 1-δ Co δ O x , δ = 0.2, 0.4 and 0.6) were developed and applied for NH 3 -SCR of NO x at low temperature. Compared with Hierc-MnFeO x , Hierc-MnFe 1-δ Co δ O x catalyst exhibited enhanced low-temperature activity and a broadened temperature window (NO x conversion above 80% was between 90 and 343 °C over Hierc-MnFe 0.6 Co 0.4 O x), as well as better H 2 O resistance and SO 2 tolerance. The enhanced low-temperature activity was attributed to a larger amount of active oxygen species, a higher proportion of Mn4+, Fe3+ and Co3+ content, and the improvement of surface acidity, which can facilitate the adsorption and activation of NO and NH 3. Additionally, the Hierc-MnFe 0.6 Co 0.4 O x catalyst exhibited superior soot tolerance due to its special hierarchically ordered architecture. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed that the Co-modified Hierc-MnFe 1-δ Co δ O x ternary oxide catalyst could efficiently protect nitrate species on Hierc-MnFe 0.6 Co 0.4 O x from the poisoning effect of SO 2 , thereby boosting its SO 2 tolerance. This study provides a good candidate for low-temperature de NO x application with enhanced SO 2 and soot tolerance. [ABSTRACT FROM AUTHOR]

• Cobalt oxide was deposited on two ceria nanoshapes with various metal precursors. • Nanorod-supported catalysts prepared with Co(acac) are most active for NO reduction. • Activity is dependent on cobalt dispersion and presence of defects. The speciation and catalytic activity of ceria supported transition metal oxides synthesized via incipient wetness impregnation are highly dependent on synthesis parameters such as the choice of metal precursor and the concentration of defects such as oxygen vacancies in the support. Here, cobalt oxide domains were synthesized on cerium oxide nanorods and commercial nanopowder via incipient wetness impregnation of cobalt (II) nitrate hexahydrate, cobalt (II) acetate, cobalt (III) acetylacetonate, and disodium cobalt (II) ethylenediaminetetraacetic acid at surface densities below monolayer coverage. Their reactivity was tested in the catalytic reduction of NO by CO. The steady-state deNOx activity at 250 °C of the catalyst prepared with cobalt (III) acetylacetonate and ceria nanorods was nearly three times greater than that of the control catalyst. From X-ray absorption spectroscopy it was seen that as-deposited cobalt precursors on a nanorod support were more highly coordinated than were cobalt precursors on comparable commercial ceria nanoparticles, possibly indicating anchoring at defects on the nanorods. A relationship was found between catalyst activity and the cobalt oxidation state of the fully calcined catalysts that suggests that deNOx activity is separately dependent on the cobalt oxide distribution and the presence of defects in the support. Overall, here it is shown that the two critical synthesis parameters of ligand choice and defected supports combine additively to improve reactivity of the supported cobalt oxide. [ABSTRACT FROM AUTHOR]

• Alkali co-cations Na+ and K+ stabilize SSZ-13 during hydrothermal aging. • Alkaline earth co-cation Ca2+ destabilizes SSZ-13 during hydrothermal aging. • Repulsive interactions between Cu ions and co-cations prevents Cu overloading. • At optimized co-cation and Cu ratios, both SCR performance and catalyst stability improve substantially. Cu,M/SSZ-13 (M = Na+, K+ and Ca2+) selective catalytic reduction (SCR) catalysts with Si/Al = 6 and M/Cu ratios varying from 0.1 to 1.0 are prepared by solution ion exchange, followed by slurry drying and hydrothermal aging at 800 °C. The catalysts are characterized with X-ray diffraction and N 2 adsorption isotherms to probe their textural properties; 27Al and 29Si nuclear magnetic resonance and NH 3 temperature-programmed desorption to probe their acidity properties and levels of dealumination; and electron paramagnetic resonance and H 2 temperature-programmed reduction to quantitatively explore the nature of Cu moieties in the catalysts. These studies are followed by density functional theory calculations to elucidate Cu and co-cation interactions at an atomic level and SCR reaction tests to reveal correlations between the chemical and physical properties of the catalysts and their SCR performance. Through these comprehensive investigations, it is discovered that alkali metal co-cation addition can be used for the synthesis of highly stable, and highly active and selective Cu/SSZ-13 catalysts with relatively high Al content. In catalysts with optimal alkali incorporation, dealumination of the SSZ-13 substrate is largely inhibited, allowing high concentrations of SCR-active isolated Cu ions. At the same time, repulsive interactions between Cu ions and alkali metal co-cations preclude excessively high isolated Cu-ion loadings. Interplay between and optimization of these two factors is considered the underlying origin for this successful catalyst synthesis strategy. On the other hand, the alkaline earth co-cation Ca2+ fails to demonstrate any beneficial effects, since it destabilizes isolated Cu ions via site competition. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Cobalt oxide was deposited via incipient wetness impregnation on three ceria nanoshapes. • Nanorod supported catalysts are most active for NO reduction at range of Co surface densities (0.1–11 Co nm−2). • Co oxidation state of fully oxidized catalyst correlates with NO reduction activity. • Oxygen vacancy defects in ceria may partially reduce and stabilize Co, leading to improved activity. Abstract When using nanocrystalline oxides as catalytic supports, different nanoshapes have different numbers of oxygen vacancy defects, surface energies, and surface terminations; these properties may affect the dispersion, oxidation state, and therefore catalytic activity of a second supported metal oxide. Here, cobalt oxide domains were synthesized on cerium oxide nanorods, nanocubes, and commercial nanopowder via incipient wetness impregnation of cobalt (II) nitrate hexahydrate at several surface coverages. The resulting materials were examined for their reducibility under CO and H 2 and their reactivity in the catalytic reduction of NO by CO from 200 to 450 °C. Activity per total mass of catalyst is highest at intermediate loadings, while activity per Co atom is maximized at the lowest loadings, implicating highly dispersed Co-O-Ce sites as the active species. Across all Co loadings, catalysts with nanorod supports have higher activity than catalysts made with ceria nanoparticles or nanocubes. From X-ray absorption spectroscopy, it was found that the more-active nanorod supports are better able to maintain Co in a partially reduced state under reaction conditions after initial calcination. This stabilization appears to be further correlated with the high number of defects on the ceria nanorods observed via Raman spectroscopy, rather than with properties of the exposed crystal plane, as has been traditionally reported for these materials. These insights may lead to new generations of selective catalysts based on nanocrystal-supported oxides for emissions abatement and other important reactions. [ABSTRACT FROM AUTHOR]

Three Fe-ZSM-5 catalysts (0.15-0.46 wt.% Fe) prepared via different routes with Fe ions present in extra-framework single sites as well as in oxidic clusters have been catalytically tested and monitored by operando EPR and UV-vis spectroscopy under standard and fast SCR conditions. In both cases, Fe ions in single α positions and oxidic clusters remain essentially trivalent while significant differences are evident for the remaining sites. During standard SCR, Fe sites in β positions are completely, and those in γ positions are partly reduced to inactive FeII, which is not able to catalyze the oxidative activation of NO being essential for its subsequent reduction to N2. During fast SCR, the same β and γ sites are effectively reoxidized by NO2 and are thus kept in a redox-active state. The high reaction rates in fast SCR already at low temperatures are therefore assigned to those sites. [ABSTRACT FROM AUTHOR]

Highlights: [•] Fe-ZSM-5 is strongly activated for NO oxidation by previous contact with SCR feed. [•] Rates of NO oxidation to NO2 and of standard SCR are uncorrelated. [•] NO2 formation is not a mechanistic step of standard SCR. [•] Under conditions of standard SCR, NO oxidation is inhibited by NH3. [ABSTRACT FROM AUTHOR]

Abstract: A high-throughput approach, aided by multi-objective experimental design of experiments based on a genetic algorithm, was used to optimize the combinations and concentrations of a noble metal–free solid catalyst system active in the selective catalytic reduction of NO with C3H6. The optimization framework is based on PISA [S. Bleuler, M. Laumanns, L. Thiele, E. Zitzler, Proc. of EMO''03 (2003) 494], and two state-of-the-art evolutionary multi-objective algorithms—SPEA2 [E. Zitzler, M. Laumanns, L. Thiele, in: K.C. Giannakoglou, et al. (Eds.), Evolutionary Methods for Design, Optimisation and Control with Application to Industrial Problems (EUROGEN 2001), International Center for Numerical Methods in Engineering (CIMNE), 2002, p. 95] and IBEA [E. Zitzler, S. Künzli, Conference on Parallel Problem Solving from Nature (PPSN VIII), 2004, p. 832]—were used for optimization. Constraints were satisfied by using so-called “repair algorithms.” The results show that evolutionary algorithms are valuable tools for screening and optimization of huge search spaces and can be easily adapted to direct the search towards multiple objectives. The best noble metal free catalysts found by this method are combinations of Cu, Ni, and Al. Other catalysts active at low temperature include Co and Fe. [Copyright &y& Elsevier]

Abstract: A multistep mechanism has been elucidated for the reduction of NOx in the presence of ethanol over silver-exchanged zeolite Y (Ag/Y). Ethanol reacts with O2 and/or NO2 to form acetaldehyde at temperatures as low as 200 °C. Surface acetate ions, formed from the oxidation of acetaldehyde, react with NO2 to yield nitromethane, a critical intermediate in subsequent deNOx chemistry. CN−, NC−, and NCO− are intermediates likely bound to silver ions. Both CN− and NC− are stable toward reaction under experimental conditions. A significant difference exists between the catalytic activities of Ag/Y and Ag/γ-Al2O3; oxidation of ethanol to acetate at low temperature is significantly faster over Ag/Y than over Ag/γ-Al2O3, and both NO2 and O2 are effective oxidants over Ag/Y. With Ag/Y, pretreatment with either O2 or H2 does not affect the yield of N2, which approaches 60% and remains constant for at least 5 h, making this catalyst promising for NOx reduction. [Copyright &y& Elsevier]