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CuO/CeO2 catalysts were widely studied as an alternative to precious metal catalysts, and the Cu–Ce synergy was essential to improve the catalytic performance. In this paper, the effects of CuO loading on Cu–Ce synergy in CuO/CeO2 nanorod catalysts and their performance in toluene combustion were systematically investigated. It was found that non-equilibrium plasma facilitated the dispersion of CuO active species on the CeO2 surface. With the increase of the CuO loading from 1 wt% to 4 wt%, the Cu–Ce synergistic effect was gradually improved, which generated Cu+/Cu2+ and Ce3+/Ce4+ redox electron pairs. The highest oxygen vacancy concentration and Cu+ content of CuCe-4 (4 wt%) resulting from strong Cu–Ce synergy accelerated the activation of chemisorbed oxygen and consequently improved the efficiency of toluene catalytic combustion. [ABSTRACT FROM AUTHOR]

Plasma catalysis is recognized as a promising technology for the elimination of diluted volatile organic compounds (VOCs). In this study, a hybrid process was carried out using dielectric barrier discharge (DBD) and MCeZr/TiO2 (M = Cu, Mn, Ni, and Co) catalysts for the degradation of VOCs. The plasma-catalytic system demonstrated a substantial improvement in toluene conversion and CO2 selectivity compared to the plasma-only system owing to the synergistic effects of plasma and thermal catalysis on toluene degradation. The performance of toluene removal follows the sequence of CuCeZr/T > NiCeZr/T > CoCeZr/T > MnCeZr/T in plasma catalysis. The CuCeZr/T catalyst demonstrated the highest toluene conversion of 99.0% and a CO2 selectivity of 91.0% at a discharge power of 30 W. Energetic electrons and reactive species generated by plasma actively participate in toluene activation in the gas phase and facilitate adsorption on the catalyst surface. The redox properties between Ce4+/Ce3+ and Cu+/Cu2+ species dictated the reducibility of the CuCeZr/T catalyst, promoting oxygen cycling during toluene oxidation and leading to enhanced catalytic performance. The pathways of toluene destruction in the plasma-catalysis system are discussed based on the analysis results of GC–MS, optical emission spectroscopy and calculations of the electron-impact reactions. [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]

• Discern the distinct functions of superficial oxygen and lattice oxygen during the combustion of propane and soot. • Isotopic oxygen exchange experiments provide evidence for lattice oxygen migration in catalysts. • Cu-Ce solid solution at phase interface as portholes for the migration of active oxygen. • Direct evidence of M-K mechanism in propane and soot catalytic combustion is provided. Determining the migration rules of oxygen species in catalytic combustion, especially for catalysts composed of transition metal oxides, is essential yet challenging. This study hydrothermally synthesized nanosphere-structured cerium dioxide (CeO 2) and its copper-loaded catalysts (Cu/CeO 2) to identify the distinct functions of superficial oxygen species (O) and lattice oxygen (O2–). The presence of Cu-Ce solid solution at the Cu/CeO 2 interface lowered the apparent activation energy for the catalytic combustion of propane and soot. The catalytic combustion of propane followed the Mars-van Krevelen mechanism, with O2– serving as the dominant reactive phase while O played a subordinate role. The solid–solid reaction between soot and superficial oxygen of the catalyst was responsible for catalyzed soot combustion. The O species produced by surface defective sites exhibited higher activity than O2–, which drained easily at the beginning of the reactions. The isotopic oxygen exchange tests revealed the mechanism of metal oxide (CuO/CeO 2) interactions for active oxygen species migration, with the results demonstrating the solid solution at the phase interface as portholes for oxygen migration, thus increasing oxygen mobility between the gaseous phase and the surface by lowering the migration activation energy. In situ, infrared results showed that the reaction path of soot catalytic combustion was single, without any intermediate production formation, compared to multiple paths in the propane oxidation process. This study provided an easily implemented and widely applicable method, which deepens our understanding of the characterization of the function and migration of predominant oxygen species in diverse combustion reactions involving oxide-based catalysts. Additionally, this study clarified differences and similarities between the reaction mechanisms of solid–solid and solid–gas catalysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synergy of Cu-Ce interface and SSZ-13 promotes NH 3 -SCO reaction. • –NH mechanism dominates the low-temperature reaction with key imide –HNO. • NH x species tend to form crucial N 2 H 4 intermediates with temperature rising. • i-SCR reaction at high temperature can improve NO x reduction and N 2 selectivity. • Cu site migrates from 8-MRs to 6-MRs enhancing lattice oxygen transfer. The selective catalytic oxidation (SCO) has proved to be one of the most effective strategies for NH 3 removal, and the corresponding reaction mechanism remains a key and challenging issue. This study provides the NH 3 -SCO reaction pathways at different reaction stages on Cu-Ce/SSZ-13 catalysts mainly based on kinetic experiments and quantitative analysis of active sites. Mars-van Krevelen (M−K) mechanism is determined to dominate the whole SCO reaction by the kinetic model. At low-temperature, the dehydrogenated NH 3 (NH x) reacts with lattice oxygen first to generate the key imide –HNO (–NH pathway), whereas, NH x species tend to be coupled on the catalyst surface to form N 2 H 4 (hydrazine pathway) with temperature rising. i-SCR reaction at high temperature reduces NO x production and improves nitrogen selectivity. Ce ions can promote the migration of Cu2+ in SSZ-13 skeleton from [Cu2+(OH)]+-Z in eight-membered rings to Cu2+-2Z in six-membered rings which facilitates the N 2 selectivity at high temperature. [ABSTRACT FROM AUTHOR]

The CuMn/ZSM-5 (CM/Z), CuMn/Beta (CM/B), and CuMn/SSZ-13 (CM/S) catalyst samples were prepared via an excess impregnation method to investigate the metal-support effect. The results show that the activity at 550 °C for NO direct decomposition follows the order of CM/Z (53.4%) > CM/B (49.2%) > CM/S (7.9%). The good activity and stability of CM/Z are attributed to a strong support effect including forming more active copper sites of the (Cu2+-O2--Cu2+)2+ and (Cu+-□-Cu+)2+ dimers, which have higher redox activity, capacity of oxygen mobility, and NO sorption capability. The competitive adsorption between NO and O 2 on the oxygen vacancy of dimers over CM/Z results in the activity decrease from 53.4% to 40.3% at 550 °C after adding 1 vol% O 2. The reaction mechanism over CM/Z was discussed based on the in situ DRIFT and isotopic (18O 2) experiments. Two NO adsorbs firstly on (Cu+-□-Cu+)2+ to form N 2 O, and N 2 O is activated to produce N 2 , followed by the NO adsorption on (Cu2+-O2--Cu2+)2+ to form nitrite and nitrate species and decomposition to NO and O 2. [Display omitted] ● The support effect of ZSM-5, Beta, and SSZ-13 supported CuMn is examined. ● CuMn/ZSM-5 exhibits a high NO to N 2 conversion of 53.4% at 550 °C. ● The intermediate species and competitive adsorption of NO and O 2 are discussed. ● The reaction pathways for NO direct decomposition are proposed. [ABSTRACT FROM AUTHOR]

Chemical looping combustion (CLC) and catalytic combustion (CC), which are potential technologies to promote CO→CO 2 efficient conversion and energy conservation for the steelmaking off-gas, are investigated in reaction activity, structure evolution catalysts/oxygen carriers (OCs) and energy recovery using Cu/CeO 2 materials. Activity results suggest that the rod-shaped samples with well-defined (100) crystal faces exhibit higher activity than the sphere-shaped samples with (111) crystal faces, obtaining the optimized copper content of 3 wt%. IR spectra confirmed the proposed reaction pathway that the CO adsorbed on copper sites (Cu+–CO) at the Cu–Ce interface reacts with adjacent surface lattice oxygen. The gaseous oxygen continuously migrates to the external surface of materials, thus resulting in strongly exothermic CO self-sustained combustion during CC. Such a violent reaction does not cause obvious evolution of chemical composition, crystalline phase and structure. Since the active lattice oxygen is gradually consumed but not replenished by external gaseous O 2 in time, CO combustion is not self-sustained during CLC. Therefore, the reduction cycle is no longer confined to the surface of the material but penetrates deep into its body, which accelerates Cu+ enrichment at the surface and leads to irreversible sintering and agglomeration of the material. • The activity of nanorod and nanosphere Cu/CeO 2 was compared. • CLC reaction is more exergy efficiency when burning. • The reason of catalyst deactivation in CLC was investigated. • The migration of active oxygen species in CC and CLC was compared. [ABSTRACT FROM AUTHOR]

• Ea of intermediate species is calculated during toluene oxidation. • Relationship between the activation energy of the overall and primitive reaction. • Transient response experiments of isotopically labeled oxygen. • M−K mechanism dominates in the oxidation of toluene. Catalytic properties of multiple metals deposited on TiO 2 nanoparticles were investigated in the oxidation of toluene. Isovolume impregnation method prepared the catalysts containing Cu, Mn, Ni, Co, and Fe deposited on TiO 2 , including CeO 2 and ZrO 2. The effects of loaded metal oxides on the structure and activity of initial catalysts were investigated using various characterization techniques. Toluene's removal efficiency and CO 2 selectivity in the catalyst system were classified as follows: CuCeZr/T > MnCeZr/T > NiCeZr/T > CoCeZr/T > FeCeZr/T. Presence of water vapor exhibits an inhibitory effect on the conversion of toluene, which diminishes at higher temperatures. One contribution of this paper is to obtain the oxidation pathway of toluene and the relationship between the activation energy of all-inclusive and elementary reactions based on the variation of infrared spectrum using Freeman-Carroll method. Another contribution is to clarify the share of Langmuir-Hinshelwood and Mars-van Krevelen mechanisms during the oxidation of toluene over CuCeZr/T catalyst by transient response experiments of isotopically labeled oxygen. These findings provide a feasible method for the design and synthesis of transition metal oxide catalysts for industrial applications. [ABSTRACT FROM AUTHOR]

Self-sustained catalytic combustion is a sustainable approach to deal with exhaust gas with high concentration CO, and revealing its reaction process is necessary and challenging. Herein, cube (Cu 2 O-C), octahedron (Cu 2 O-O) and dodecahedron (Cu 2 O-D) exposing different crystal planes were used to explore the catalytic combustion mechanism. The catalytic combustion can be self-sustained on the Cu 2 O surface and the activities decrease in the order of Cu 2 O-O > Cu 2 O-D > Cu 2 O-C, contributing to the different exposing planes with (1 1 1), (1 1 0) and (1 0 0), respectively. In-situ DRIFTS results prove that the catalytic combustion of CO to CO 2 on Cu 2 O is prone to follow the MvK mechanism. Comparing with Cu 2 O-D and Cu 2 O-C, the relatively open surface of Cu 2 O-O plane composed of unsaturated copper and oxygen atoms facilitates the CO adsorption on Cu (I) and the mobility of lattice oxygen, leading to the highest low temperature reducibility and catalytic activity. [Display omitted] • CO self-sustained catalytic combustion were achieved on cube, octahedron and dodecahedron Cu 2 O. • Octahedron Cu 2 O with (1 1 1) planes exhibits the best activity for high concentration CO. • Coordination unsaturated Cu and O on the (111) and (110) planes promote CO oxidation. • Catalytic combustion reaction of CO on Cu 2 O mainly follows the MvK mechanism. [ABSTRACT FROM AUTHOR]