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[Display omitted] • A class of Ru-Co single-atom alloy catalysts (marked as Ru x Co 1 SAA, x stands for Ru/Co molar ratio) were prepared. • The electronic structure of Ru x Co 1 SAA could be effectively tuned by regulating the Ru/Co molar ratio. • A moderate ratio of Ru/Co (1.7:1) favors superior NH 3 synthesis rate. • The excess Ru destroys the SAA structure, resulting in the diminution of SAA advantages. Rational design of efficient catalysts for ammonia (NH 3) synthesis at mild conditions is of paramount importance for the development of electrolysis driven Haber-Bosch (e HB) process. Ammonia synthesis is a structure sensitive reaction, and any small change of electronic structure could result in dramatic change of catalytic activity, especially for the Ru-based NH 3 synthesis catalysts. Electronic structure modulation of the Ru-based catalysts could provide desirable catalytic activity. Herein, we explore a class of Ru-Co single-atom alloy catalysts (marked as Ru x Co 1 SAA, x stands for Ru/Co molar ratio), in which Co single atoms are located on Ru nanoclusters to form Co-Ru coordination, and then electronic structure of Ru x Co 1 SAA could be effectively tuned by regulating the Ru/Co molar ratio. Our studies show that a moderate ratio of Ru/Co (1.7:1) favors superior NH 3 synthesis rate and low activation energy. Using a suite of elaborate characterizations, we have observed that the outstanding performance over Ru 1.7 Co 1 SAA can be attributed to the electron redistribution between Ru and Co atom, resulting in an upshift of d band center and lowering of work function. However, there is decrease of NH 3 synthesis rate when Ru/Co molar ratio is 2, due to the partial detachment of Ru entities from SAA structure, and the formed individual Ru nanoparticles (NPs) overlay the surface of catalyst. In such a case, N 2 activation behavior over Ru 2 Co 1 is alike that of Ru NPs catalysts. The present study demonstrates that the Ru/Co ratio in SAA structure can effectively regulate the electronic structure of catalyst for NH 3 synthesis rate enhancement. [ABSTRACT FROM AUTHOR]

• ε-MnO 2 with abundant structure defects was applied in CO oxidation. • Acid washing highly improved catalytic activity of ε-MnO 2. • Enriched surface hydroxyl is the intrinsic reason for the catalytic improvement. • Bicarbonate intermediate desorbs CO 2 faster than carbonate intermediate. Herein, we synthesize the hydroxyl-enriched ε-MnO 2 catalyst (MnO 2 -AT) by simple acid washing. Acid washing destroys the sphere structure into fragments with abundant structure defects and maintains the crystal and pore structure of ε-MnO 2. MnO 2 -AT exhibits the high activity and selectivity for preferential oxidation of CO in the H 2 -rich stream, as well as the high activity for CO total oxidation. It can completely converts CO in preferential and total oxidation of CO at 170 °C and 90 °C, respectively, with a good stability. The acid washing treatment highly increases the surface hydroxyl groups on MnO 2 -AT. Our results demonstrate that with the aid of surface hydroxyl groups CO can easily form bicarbonate intermediates, which are more thermally unstable than carbonate intermediates. The faster CO 2 desorption from bicarbonates than carbonates promotes the CO oxidation process. [ABSTRACT FROM AUTHOR]

• A dynamic N- and H-involved cyclic reaction pathway proposed for NH 3 production. • A dual-path mechanism including chemical looping and thermal catalysis illustrated. • Bottleneck of direct N N dissociation bypassed. The synthesis of ammonia via the Haber-Bosch process using Fe-derived catalysts requires harsh reaction conditions. It is hence meaningful to develop catalysts for low-temperature synthesis of ammonia for industrial application. Herein for the first time, we report that with the synergy between LaN and Ru/ZrH 2 , NH 3 can be synthesized via a dual-path mechanism. The LaN-promoted Ru/ZrH 2 catalyst shows exceptionally high NH 3 synthesis rate (up to 305 mmol NH3 g Ru −1 h−1) at 350 °C under 1 MPa and remarkable durability (tested for 200 h). The outcomes of isothermal surface reaction and a suite of 15N 2 and D 2 isotopic labeling experiments reveal that the N3− of LaN reacts with H− ions to produce NH 3 , leaving behind N and H vacancies. The initial state of Ru/xLaN/ZrH 2 can be restored by having the N and H entities replenished under the atmosphere adopted for NH 3 synthesis. Moreover, based on the results of N 2 reaction order, nitrogen K-edge NEXAFS, in situ XPS as well as in situ DRIFTS analyses under a 25%N 2 -75%D 2 atmosphere, it is reckoned that the direct dissociation of N 2 does not occur on the LaN-promoted Ru/ZrH 2 catalyst while N 2 hydrogenation takes place via an associative pathway under mild conditions. For the hydrogenation of N 2 , an appropriate amount of LaN would induce a synergic effect on the Ru active sites, leading to facile activation and hydrogenation of N 2 to *N 2 H 2. Nonetheless, an excess amount of LaN would result in blocking of Ru sites, consequently hindering the formation of *N 2 H 2 and decreasing the catalytic activity. Following the associative and chemical looping pathways, the LaN-promoted Ru/ZrH 2 catalyst bypasses the bottleneck of N 2 direct dissociation, making the synthesis of NH 3 at mild conditions possible. [ABSTRACT FROM AUTHOR]

• Cu-SAPO-44 is synthesized in one-pot using a copper-amine complex. • Cu-SAPO-44 exhibits excellent NH 3 -SCR activity over a wide temperature window. • Isolated Cu2+ ions are active sites. • A Cu2+↔ Cu+ redox cycle is confirmed by in situ XAFS. A small-pore Cu-chabazite zeolite, Cu-SAPO-44 was synthesized using a one-pot approach by combination of cyclohexylamine template and copper-amine complex. The Cu-SAPO-44 zeolite obtained exhibits excellent activity over a wide temperature window from 200 to 500 °C for the selective catalytic reduction of NO x with ammonia (NH 3 -SCR). The copper-amine complex allowed direct introduction as well as a high dispersion of extra-framework Cu species in the chabazite structure. In situ X-ray absorption fine structure (XAFS) confirmed the isolated Cu2+ ions and Cu2+ ↔ Cu+ cycle. Temperature-programmed reduction with H 2 (H 2 -TPR) and in situ FTIR of CO adsorption demonstrated that a variety of isolated Cu2+ ions inside the large cages and in or near the six-membered rings of the chabazite structure are responsible for the wide temperature window of activity. Cu-SAPO-44 has shown to be a promising candidate as a SCR catalyst with great potential in after-treatment systems for either mobile or stationary sources. [ABSTRACT FROM AUTHOR]

Identification of catalytically active species and reaction pathway in catalytic solid (catalyst)-solid (reactant) reactions is a nontrivial task as exemplified in diesel soot oxidation (combustion), the technology for control of diesel particulate emissions. A physical contact between catalytically active species and solid soot is usually deemed necessary. Herein, thermally-stable hollandite-type α-MnO 2 (K x Mn 8 O 16 ) nanorod catalysts have been synthesized with one-dimensional tunnel structures partially filled with relatively mobile K cations. These tunnel-confined quasi free K cations are revealed to be responsible for the catalytic soot oxidation activity, proving that physical contact between soot and K cations is unnecessary for solid-solid reaction. A novel catalyst, K y Ti 8 O 16 has been successfully designed to boost the catalytic activity in TiO 2 toward soot oxidation by engineering a K-contained hollandite-type isostructure. [ABSTRACT FROM AUTHOR]

Herein, we report the high catalytic activity of the potassium-promoted Co 3 O 4 nanowires supported on the monolithic three-dimensional macroporous (3-DM) nickel foam substrate (xKCo-NW) for soot combustion. The 3-DM structure of Ni foam and the space among these nanowires can extremely improve the contact efficiency between soot and catalysts. Loading of potassium provides the new active sites for soot oxidation, improves catalyst-soot contact as a molten salt and increases the number of the surface adsorbed oxygen species. The 5KCo-NW catalyst loaded with 5% potassium shows the highest catalytic performance, as well as a high water resistance. There are two types of potassium species in the catalysts, most potassium species is in the form of separate phases, and few interacts with cobalt oxide. The interaction between potassium species and cobalt oxide stabilizes a part of potassium species, and the stabilized potassium species can promote the catalytic activity for the consecutive soot combustion cycle. Moreover, our results show that the chemisorbed NO x species on the 5KCo-NW catalyst are more active than the gaseous NO 2 for soot oxidation. In the presence of O 2 , soot combustion is accelerated to react with the chemisorbed NO x species; whereas the formed nitrate/nitrite species are catalytically inert. [ABSTRACT FROM AUTHOR]

Development of efficient electrocatalysts requires construction of catalytic surfaces with moderate H adsorption energy. Here, we address this challenge by Br-induced formation of P-poor defective nickel phosphide and show that the H adsorption energy can be optimized by regulating the vacancy concentration. We show that when such defective Ni 12 P 5−x Br x nanoparticles are distributed on the surface of Ni 2 P nanosheets (Ni 12 P 5−x Br x /Ni 2 P NS), excellent catalytic activity for water splitting is obtained in alkaline media. Density functional theory computations revealed that Br doping induce the formation of a P-poor nickel phosphide with vacancies, leading to an optimal H adsorption strength with a volcano-type relationship. This is the best reported for a non-precious metal phosphide at present: the overpotential for HER is 18 mV at 10 mA cm−2 and 155 mV for OER. This leads to an exceptionally low cell voltage requirement of only 1.44 V to drive overall water splitting in an alkaline electrolyzer. [Display omitted] • Br-induced nickel phosphide formation energy change achieves P-poor defective phase configuration. • Multi-level regulation of vacancy content, morphology and catalytic performance by temperature is achieved. • DFT calculations show that Ni 12 P 5−x Br x shows a volcano-type relationship related to vacancy content. [ABSTRACT FROM AUTHOR]

Two typical K-supported oxides (K/Al 2 O 3 and K/TiO 2 ) were selected as catalysts for diesel soot combustion in order to evaluate the relationship between activity and stability. The surface species were first characterized by X-ray powder diffraction (XRD), X-ray absorption fine-structure (XAFS), infrared analysis (IR), X-ray photoelectron spectroscopy (XPS), in situ IR of CO 2 adsorption and temperature-programmed desorption of CO 2 (CO 2 -TPD). Then the activity was studied by temperature-programmed oxidation (TPO), temperature-programmed reduction with soot (Soot-TPR) and in situ IR of soot combustion reactions. Lastly, the stability of the catalyst was checked by washing with water and analysis for K. This showed that K/TiO 2 displayed negligible activity due to the immobilization of K + ions in TiO 2 to form K 2 Ti 6 O 13 . However, K/Al 2 O 3 exhibited superior activity owing to the presence of active free K + ions on the surface. The downside is the leaching of K + ions into the effluent containing some water vapor, resulting in its poor stability – the other side of the coin for the highly active free K species. One of the suggested strategies for making a balance between activity and stability is encapsulating active K species in the channel of the catalyst as demonstrated by the tunneled cryptomelane. [ABSTRACT FROM AUTHOR]

Highlights: [•] The controllable preparation of active Au/NiOx for CO oxidation was presented. [•] [Cl−] during the washing of catalyst precusors is an indicator for the activity. [•] CO total oxidation can be realized below 0°C if the [Cl−] was >4 but <8ppm. [•] The active nano-Au catalyst possesses nano-Au with smaller particle. [•] The Au–Au coordination number in the active catalyst is 7.66. [Copyright &y& Elsevier]

[Display omitted] • Developing the coordinative unsaturation (Fe-N 2) with nitrogen vacancies. • Nitrogen vacancies and Fe-N 2 active site for boosting electrochemical artificial N 2 fixation. • In situ environmental TEM directly visualize N 2 adsorption on FePcTa-PPy. • Fe-N 2 -opp possesses lower overpotential and excellent dynamics stability for ENRR. The construction of definitive correlation between structure and catalytic properties for electrochemical artificial N 2 fixation is still challenging yet significative. Herein, we have explored the coordinative unsaturation (Fe-N 2) in isolated Fe atoms with nitrogen vacancies (V N, which are located at the opposite coordination sites of the Fe atom) on interconnected carbon for electrocatalytic ammonia synthesis. Benefiting from dual active centers (Fe-N 2 and V N) and the spin density on both of them, the novel catalyst exhibits a synergistic improvement of catalytic activity, selectivity, and stability. This work guides the design of the catalyst theoretically and synergistically and combines the advantages of Fe-N 2 with V N structure creation, defect and spin-state engineering introduction toward the concurrent fulfillment of effective N 2 adsorption and activation. We believe our strategy will incite more investigation into designing high-performance catalysts with well-defined coordinative unsaturation single-atom active sites for ambient ammonia synthesis and other energy conversion system. [ABSTRACT FROM AUTHOR]

A novel structure of Fe-doped NiO coupled Ni cluster hollow nanotube arrays (Fe-NiO-Ni CHNAs) composed of defect-rich NiO phase and Ni clusters anchored on outside of nanotubes is presented. The d-band downshifted by Fe-doping, coupled of Ni clusters and defect-rich nature greatly improve electrocatalytic performances of Fe-NiO-Ni CHNAs toward oxygen evolution reaction. • A multi-level structure of Fe-doped NiO coupled Ni cluster hollow nanotube arrays (Fe-NiO-Ni CHNAs) was synthesized as a catalyst for OER. • Fe-NiO-Ni CHNAs exhibits overpotential of 245 mV at 10 mA cm−2 and outstanding durability that surpasses most of transition metal oxides. • The improved OER activity is mainly because Fe doping downshifts the d-band of metal sites. • Fe-NiO-Ni CHNAs obeyed the adsorbate evolution mechanism with a nonconcerted proton-electron transfer pathway. Herein we present a novel multi-level structure of Fe-doped NiO coupled Ni cluster hollow nanotube arrays (Fe-NiO-Ni CHNAs) grown on carbon fiber cloth as an efficient catalyst for oxygen evolution reaction. In this multi-level structure, rocksalt-type Fe-doped NiO phase hybrids with Ni clusters coupled into the nanospheres anchored to the outside of nanotube, forming a unique 3D corn-like structure. This novel multi-level structure represents a large specific area for catalytic reaction. X-ray absorption fine structure indicates that the defect-rich Fe-doped NiO phase has abundant coordinative unsaturated sites as active sites, and Fe doping downshifts the d-band of metal sites, which is the main contribution to the improved oxygen evolution reaction catalytic activity. The OER of Fe-NiO-Ni CHNAs obeys the adsorbate evolution mechanism with the nonconcerted proton-electron transfer pathway as a rate-determining step. Thus Fe-doped NiO CHNAs exhibits excellent OER performance and outstanding durability that surpasses most of transition metal oxides. [ABSTRACT FROM AUTHOR]