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The Cu/ZSM-5, Ce/ZSM-5 and Cu-Ce/ZSM-5 catalysts were prepared and characterized in this investigation and the catalytic activity of carbon monoxide (CO) combustion under these catalysts was determined by temperature-programmed oxidation. The activity for the CO combustion follows the decreasing order: Cu-Ce/ZSM-5 > Cu/ZSM-5 > Ce/ZSM-5, indicated by lower ignition, light-off, extinction temperature and broader hysteresis determined via both heating and cooling feeding process. The CO adsorbed on the copper sites to form Cu + –CO complexes, monodentate and bidentate carbonates was considered to be the crucial step for CO catalytic combustion. At the CO concentration ≥5 vol.%, the CO self-sustained combustion was achieved over the Cu-Ce/ZSM-5 catalyst. One reason is due to formation of Cu 2+ ions incorporated into cerium oxides, which are more reducible than the copper clusters, minicrystals and bulk CuO particles. Another reason is attributable to the formation of Ce 4+ /Ce 3+ redox couple, which facilitates oxygen transport on the catalyst surface. [ABSTRACT FROM AUTHOR]

Highlights: [•] Zirconia introduction favors copper dispersion and inhibits copper crystallization. [•] Zirconia addition is beneficial to enriching copper species on the ZSM-5 surface. [•] The interaction between copper and zirconium enhances the lattice oxygen and site reducibility. [•] The Cu-Zr/ZSM-5 presents a wide activity window within the range of diesel exhaust temperatures. [ABSTRACT FROM AUTHOR]

Self-sustained catalytic combustion is a promising strategy to remove CO from the off-gas produced during steelmaking, where the potential catalysts are bulk copper-cerium-zirconium mixed oxides or those supported on TiO 2 or ZSM-5 substrates. In this study, the effects of the catalyst support on the CO catalytic ignition performance and reaction pathways were investigated by FTIR coupled with a novel in-situ cell, together with the state-of-the-art characterization techniques. The Infrared (IR) transmission cell equipped with a magnetically driven system, could effectively prevent overlaps between active intermediate peaks (Cu+-CO and Cu+(CO) 2) and gaseous CO peaks. The Cu+ cations located at the phase interface are the main active sites. The Cu and Ce interactions lead to the formation of solid solutions of CuCe 0.75 Zr 0.25 O δ (CuCeZr). The monocarbonyls [Cu+-CO] are the dominant species during CO oxidation, and the vacancies in the solid solutions are occupied by oxygen, accelerating the oxygen cycle. The TiO 2 or ZSM-5 supports promote copper dispersion over CuCe 0.75 Zr 0.25 O δ /TiO 2 (CuCeZr/T) and CuCe 0.75 Zr 0.25 O δ /ZSM-5 (CuCeZr/Z) catalysts, which can be attributed to their high surface areas (168.2 and 346.3 m2/g, respectively), while the Cu-Ce interactions are less relevant. Hence, CO oxidation mainly occurs at the phase interface between copper oxide and TiO 2 /ZSM-5. Dicarbonyls [Cu+(CO) 2 ] are the main intermediates for the CuCeZr/T and CuCeZr/Z catalysts, and the Cu2+ species are reduced to form dicarbonyls that also take part in the oxidation process. Although a well copper dispersion enhances the activity of individual copper sites on the CuCeZr/T and CuCeZr/Z catalysts, considering the redshift of the carbonyl bands and the increase in CO adsorption, the close interactions and high contents of Cu and Ce favor the local accumulation of heat and mass transfer over bulk CuCeZr, leading to the ignition of CO at low temperatures. [Display omitted] • CuCe 0.75 Zr 0.25 O δ and CuCe 0.75 Zr 0.25 O δ /TiO 2 and CuCe 0.75 Zr 0.25 O δ /ZSM-5 catalysts were designed. • The structure-activity relationship was obtained. • The self-sustained combustion and stability limit of CO were carried out. • The in-situ IR with a novel magnetically driven IR cell was designed and performed. • The intermediate species and reaction pathways over different catalysts were evidenced. [ABSTRACT FROM AUTHOR]

Catalytic combustion (CC) and chemical looping combustion (CLC) are promising technologies for energy saving and emission reduction of CO 2 in treatment of steelmaking off-gas. This work firstly reports and compares the evolution behavior and quantitative reaction mechanisms of cube Cu 2 O model catalyst for CC and CLC reactions. The Cu 2 O-CC exhibited the higher activity and stability than Cu 2 O-CLC. The typical characterization results suggested that the only surface unstable Cu 2 O was oxidized to CuO, and the excellent synergistic effect of metal-oxide interface (100) between Cu+/Cu2+ and active lattice oxygen species for Cu 2 O-CC reaction. But, for CLC reaction, Cu 2 O structure was collapsed, which caused the agglomeration of CuO x species and gradual decrease of reaction stability. Three different active oxygen species (surface cycle lattice oxygen, bulk lattice oxygen, and adsorbed oxygen) and the detailed reaction pathways were proposed by the in situ IR spectroscopy, isotopic (18O 2) transient exchange experiments and DFT simulation. The intrinsic activity of surface cycle lattice oxygen was higher in terms of TOF (13.5 × 10−3 s−1) and facile formation of C16O18O on the cubic interface of Cu 2 O-CC through adsorbed CO during CC process. The contribution degrees of Mars-van-Krevelen (M-K) and Langmuir–Hinshelwood (L-H) mechanisms for CC and CLC reactions were 76.6% and 23.4% for CC, and 89.7% and 10.3% for CLC on Cu 2 O catalyst, respectively. [Display omitted] • The cube Cu 2 O model catalyst was well prepared by liquid-phase reduction method. • The detailed evolution behavior and structure-activity relationship of cube Cu 2 O was carried out for CC and CLC reactions. • The roles of three different active oxygen species in CC and CLC reactions were clearly distinguished. • The contribution degrees of Mars-van-Krevelen and Langmuir–Hinshelwood mechanisms for CC and CLC reaction were proposed. [ABSTRACT FROM AUTHOR]

CO self-sustaining catalytic combustion tends to be one of potential means to achieve efficient conversion of off-gases from steelmaking. Building model catalysts to investigate the reaction process academically is essential to design optimized catalysts and Cu 2 O exposing (1 0 0), (1 1 1) and (1 1 0) planes are excellent materials. Herein, morphological CeO 2 /Cu 2 O inverse model catalysts were synthesized to reveal the synergistic effect and reaction mechanism. It is demonstrated that the ignition temperature is lowered on the interface by synergistic effect, which dominates the ignition, while the combustion after ignition is controlled by Cu 2 O planes providing abundant lattice oxygen to react with CO. Additionally, exposure of different planes plays a significant role in the reaction since O-termination on (1 0 0) inhibits the interaction, whereas Cu-termination on (1 1 0) surface structure and coordinately unsaturated Cu+ on open (1 1 1) surface respectively contribute to their superior catalytic performance. [Display omitted] ● Inverse model CeO 2 /Cu 2 O catalysts with regular morphology were successfully prepared. ● Synergistic effect on Cu-Ce interface lowered ignition temperature, dominating the ignition. ● The catalytic activity and synergistic effect vary among planes with (1 1 1) performing the best. ● Exposure of crystal planes with higher activity assists in designing optimized catalysts. [ABSTRACT FROM AUTHOR]

• 3D microflowers Fe–NiCoP@C on the nickel foam is synthesized. • Fe dopant modulates the electron conductivity and catalytic properties of Fe-NiCoP. • The carbon layer improves the electron conductivity and stabilizes the electrolyte at the interface. • The HSAB displays a discharge voltage of 2.74 V at 0.01 mA cm−2 and the state-of-the-art power density of 621 mW g−1. Nickel cobalt phosphide (NiCoP) is emerging as a potential electrocatalyst towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, its ORR/OER activities are sluggish. Here, we investigated the roles of iron dopants in the Fe-doped NiCoP (Fe–NiCoP) in order to boost its ORR/OER kinetics. The density functional theory (DFT) calculations reveal that the Fe dopant effectively modulates the electron conductivity of NiCoP and reduces binding energies of the reaction intermediates towards rate-determining steps of ORR and OER. A binder-free 3D microflowers morphology of the Fe–NiCoP embedded in the amorphous carbon layer (Fe–NiCoP@C) catalyst on the nickel foam was prepared as the air cathode for the hybrid sodium-air battery (HSAB). The HSAB displays a discharge voltage of 2.74 V at 0.01 mA cm−2 with excellent round trip efficiency of 93.26 % at the 500th cycle and state-of-the-art power density of 621 mW g−1. [ABSTRACT FROM AUTHOR]

• Room temperature plasma-catalytic methane oxidation to oxygenates was achieved. • The effect of γ-Al 2 O 3 supported metal (Ni, Fe and Cu) catalysts on the reaction was evaluated. • The highest selectivity of oxygenates was 71.5% using plasma catalysis. • Fe/γ-Al 2 O 3 showed the highest methanol selectivity of 36.0% with a methanol yield of 4.7%. • Cu/γ-Al 2 O 3 improved the selectivity of C 2 oxygenates to 9.4%. Direct conversion of methane into chemicals and fuels under mild conditions has been considered as a 'holy grail' of chemistry and catalysis in the 21st century. Plasma-catalytic partial oxidation of methane (POM) to higher-value liquid fuels and chemicals over supported transition metal catalysts (Ni/γ-Al 2 O 3 , Cu/γ-Al 2 O 3 and Fe/γ-Al 2 O 3) has been investigated in a co-axial dielectric barrier discharge (DBD) reactor at room temperature and atmospheric pressure. The selectivity of oxygenates was 58.3% in the plasma POM reaction without a catalyst, while the combination of DBD with the catalysts enhanced the selectivity of oxygenates up to 71.5%. Of the three catalysts, Fe/γ-Al 2 O 3 showed the highest methanol selectivity of 36.0% and a significant methanol yield of 4.7%, while the use of Cu/γ-Al 2 O 3 improved the selectivity of C 2 oxygenates to 9.4%, which can be attributed to the presence of more acid sites on the surfaces of the Cu catalyst. The possible reaction pathways in the plasma-catalytic POM reaction have been explored by combined means of plasma electrical and optical diagnostics, analysis of gas and liquid products, as well as comprehensive catalyst characterization. The plausible reaction routes for the production of major oxygenate (methanol) on the Fe/γ-Al 2 O 3 surfaces have been proposed. The surface CH x species are found to be critical for methanol synthesis; they can be formed through the direct adsorption of CH x radicals generated in the plasma gas-phase reactions or through the dissociation of adsorbed CH 4 on the catalyst surface. [ABSTRACT FROM AUTHOR]