Development of spinel bimetallic oxides as low‐cost and high‐efficiency catalysts for catalytic oxidation is highly desired. However, rational design of spinel oxides with controlled structure and ...components still remains a challenge. A general route for large‐scale preparation of spinel CoFe2O4/C nanocubes transformed from organometal‐encapsulated metal–organic frameworks (MOFs) via exchange–coordination and pyrolysis combined method is reported. Strong confinement effect between organometallics and MOFs realizes reconstruction of crystal phase and composition, but not simple metallic oxides support by Co2+ introduction. Compared with Co3O4‐Fe2O3/C, MOFs‐derived cubic nano‐CoFe2O4/C with higher surface area (115.7 m2 g−1) and favorable surface chemistry exhibits excellent catalytic activity (100% CO conversion at 105 °C) and competitive water‐resisting stability (total conversion at 145 °C for 20 h). Turnover frequency of CoFe2O4/C reaches 4.26 × 10−4 s−1 at 90 °C, two orders of magnitude higher than commercial Co3O4 . Theoretical models show that oxygen vacancies (17.7%) at exposed {112} facet on the carbon interface take superiority in nanocubic spinel phase, which allows reactive species to be strongly adsorbed on nanostructured catalysts' surface and plays key roles in hindering deactivation under moisture rich conditions. The progresses offer a promising way in the development of novel spinel oxides with tailored architecture and properties for vast applications.
Confined transformation of organometal‐encapsulated metal–organic frameworks (MOFs) into novel spinel CoFe2O4/C nanocubes is achieved via an innovative methodology combining exchange–coordination and pyrolysis. Strong interaction between the organometallic guest and MOF host leads CoFe2O4/C nanocubes to exhibit superior activity for low temperature oxidation (100% CO conversion at 105 °C) and very competitive water‐resisting stability.
Display omitted
•Oxygen vacancy in ceria for toluene oxidation was regulated by Co incorporation.•Oxygen vacancy accelerated oxygen migration and redox recycles of Co3+/Co2+ and Ce4+/Ce3+.•Oxygen ...defects facilitate the initial activation and aromatic ring broken of toluene.
Herein, we developed a series of self-assembled cobalt-cerium oxides (CoCe-x) with the regulated oxygen vacancies, to enhance the decontamination of air pollution with low-temperature catalytic oxidation, in which the typical volatile organic pollutant (VOCs), toluene, acted as the target. The oxygen vacancies in catalyst was tuned by the efficient incorporation of Co atoms into the lattice structure of ceria, and therefore improved the migration of oxygen species, the formation of surface adsorbed oxygen with high activity, as well as the redox recycles of Co3+/Co2+ and Ce4+/Ce3+. Due to the abundant oxygen vacancies, the CoCe-5 (Co loading of 5 wt%) catalyst exhibited the significantly enhanced performance in the low-temperature catalytic oxidation of toluene, on which the conversion temperature of toluene (T90) shifted to 192 °C, reduced by 23% compared with the ceria. From in situ DRIFT results, the surface adsorbed oxygen and lattice oxygen with high mobility played key roles in the excellent performance of CoCe-5 catalyst, which promoted the adsorption, activation and oxidation of toluene significantly, especially accelerating the rate-determining step of toluene oxidation, the breakage of aromatic ring.
Atomic dispersed metal sites in single‐atom catalysts are highly mobile and easily sintered to form large particles, which deteriorates the catalytic performance severely. Moreover, lack of criterion ...concerning the role of the metal–support interface prevents more efficient and wide application. Here, a general strategy is reported to synthesize stable single atom catalysts by crafting on a variety of cobalt‐based nanoarrays with precisely controlled architectures and compositions. The highly uniform, well‐aligned, and densely packed nanoarrays provide abundant oxygen vacancies (17.48%) for trapping Pd single atoms and lead to the creation of 3D configured catalysts, which exhibit very competitive activity toward low temperature CO oxidation (100% conversion at 90 °C) and prominent long‐term stability (continuous conversion at 60 °C for 118 h). Theoretical calculations show that O vacancies at high‐index {112} facet of CoxOy nanocrystallite are preferential sites for trapping single atoms, which guarantee strong interface adhesion of Pd species to cobalt‐based support and play a pivotal role in preventing the decrement of activity, even under moisture‐rich conditions (≈2% water vapor). The progress presents a promising opportunity for tailoring catalytic properties consistent with the specific demand on target process, beyond a facile design with a tunable metal–support interface.
Single‐atom catalysts are achieved on tunable cobalt‐based nanoarrays through crystal facet induced atom trapping. By precisely controlling the metal–support interface, favorable surface chemistry can be provided to create configured heterogeneous Pd/CoxOy catalysts, which exhibit superior activity for low‐temperature oxidation (100% CO conversion at 90 °C) and prominent long‐term stability.
Display omitted
•Metal oxide-based catalysts and carbon-based catalysts used for low temperature H2S-SCO were reviewed.•Internal and external factors jointly affect the desulfurization performance of ...the catalyst.•Carbon-based catalysts rely on O* for H2S catalytic oxidation, while MO-based catalysts rely on the properties of different metals.•Thermal regeneration, CS2, and ammonium hydroxide solution washing are effective methods for regenerating spent catalysts.
H2S has become a significant environmental problem because of its high toxicity, corrosiveness, and low olfactory threshold. Therefore, the high-performance removal of H2S has become a research focus. Low-temperature (<180 °C) H2S selective catalytic oxidation (H2S-SCO) technology has the advantages of high desulfurization accuracy and no secondary pollution. This technology is especially suitable for effectively removing H2S, and the catalysts play a critical role. Metal oxide (MO)-based catalysts (single metal oxides catalysts, mixed metal oxides catalysts, oxide-supported catalysts), and carbon-based catalysts (activated carbon, carbon nanofibers, carbon nanotubes, graphene-based materials, and alkaline mesoporous carbon) used for H2S removal are comprehensively discussed. This review summarizes the research progress of various catalysts for H2S-SCO, and compares their advantages and disadvantages. The influencing factors including internal factors such as basic surface/groups, structural defects, sulfur storage space, and external factors such as humidity, temperature, O2, GHSV of catalysts performance, and possible catalytic oxidation mechanisms of catalysts are systematically expounded. Out of all the catalysts reviewed, oxide-supported catalysts have shown desirable effects in H2S removal. The regeneration methods for different catalysts are also reviewed and it was found that the high porosity of catalysts with large specific surface areas is crucial for maintaining good regeneration capacity. Compared with thermal regeneration, CS2, and ammonium hydroxide solution washing regeneration are more cost-effective and worthy of further research as regeneration methods. Finally, it is recommended that additional investigation is required to understand the mechanism of interaction between H2S, and catalysts and to identify the effects of H2S, organic sulfur, ammonium hydroxide, and CO2 on catalyst activity.
Spherical cerium dioxide (CeO2–S) nanoparticles were successfully prepared using a solvothermal method, and their performances in catalytic oxidation reactions were studied. The CeO2–S catalyst ...showed superior low-temperature catalytic activity for styrene removal (T90 = 118 °C, GHSV = 18,000 h−1) compared with commercial CeO2. The characterization results showed that there were numerous oxygen defects in CeO2–S that were key to its catalytic performance at low temperatures, high redox properties, and high adsorption capacity for the reaction gases (O2 and styrene). Moreover, the catalytic performance of CeO2–S was highly stable (132 h), and the particles were reusable. FTIR and in-situ DRIFTS results showed that the type of intermediates formed during the oxidation of styrene determined the CeO2 catalytic stability, and the main intermediates were bidentate carbonate species that accumulated on the surface of deactivated CeO2–S and were not thermally stable. Moreover, the soft carbon that also deposited on CeO2–S during the reaction was easily decomposed at higher temperatures. The role of the oxygen vacancies on the CeO2–S catalyst was further revealed by correlating the concentration of oxygen vacancies and the accumulation of coke on the catalyst surface.
Display omitted
•Defect-rich CeO2–S shows super Low-temperature catalytic degradation of gas phase styrene (T90 = 118 °C).•CeO2–S catalyst exhibits excellent catalytic stability (132 h) and reusability.•Identify the main intermediates (carbonate) during styrene oxidation process by in-situ DRIFTS.•A quantitative correlation between the concentration of oxygen vacancy and coke accumulation is established.
Display omitted
•Copper-manganese layered double hydroxide precursor is successfully synthesized by a simple coprecipitation method.•CMO-400 exhibits high catalytic activity and stability for ...catalytic oxidation of toluene.•The oxidation reduction cycle of Mn3++Cu2+=Mn4++Cu+ promotes surface electron transport on the catalysts.•The reaction mechanism and intermediates of catalytic oxidation of toluene are investigated by in-situ DRIFTS.
A series of CuMn mixed oxides catalysts (CMO-T) were prepared by calcination of CuMn layered double hydroxides (CuMn-LDH) for catalytic oxidation of toluene. The obtained CMO-400 catalyst exhibited a high catalytic activity with T50 and T90 of 210 and 231 °C (WHSV = 30000 mL·g−1·h−1). Meanwhile, the CMO-400 exhibited high stability and durability even at 20 vol% water vapor. The effects of calcination temperature on the texture and structural properties were investigated systematically, which proved the formation of copper-manganese solid solution with abundant multiple-phase interfaces. In addition, the strong interaction between Cu and Mn could lead to more surface adsorbed oxygen due to oxidation reduction cycle of Mn3++Cu2+=Mn4++Cu+. Accordingly, for CMO-500 catalyst, the formation of spinel Cu1.5Mn1.5O4 phase prevented good dispersion of the manganese-oxide phases and weakened the reducibility and oxygen mobility. In-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) revealed that the intermediates accumulated continuously were difficult to be oxidized rapidly without the replenishment gaseous oxygen. Moreover, the complete transformation of the intermediate benzoate may be the key rate-controlling step in the reaction. The Facile method of preparing mixed-metal solid solution from LDH precursor system could be widely developed for the design of transition metals in catalytic oxidation of toluene.
This work reports the enhanced catalytic performance of Ag/ZSM-5 and investigates the effect of water on the decreased catalytic activity of Ag/ZSM-5 for ethylene oxidation at room temperature.
...Display omitted
•This is the first time to report on ethylene oxidation over microporous catalysts at or below room temperature.•Ag/ZSM-5 catalysts exhibit high catalytic activities and stabilities for ethylene oxidation at or below room temperature.•The reasons for Ag/ZSM-5 catalyst deactivation was comprehensively studied.•These results are helpful to seek meaningful and effective environmental materials for ethylene elimination.
Ag/ZSM-5 catalysts with different SiO2/Al2O3 ratios were prepared and evaluated for ethylene oxidation at 25 °C. Ethylene can be completely oxidized into CO2 by all the Ag/ZSM-5 catalysts at 25 °C. It is found that SiO2/Al2O3 ratio of ZSM-5 has a significant effect on catalytic stability. Ag/ZSM-5 with SiO2/Al2O3 ratio of 38 exhibits enhanced catalytic stability compared with other Ag/ZSM-5 catalysts. The conversion of ethylene with Ag/ZSM-5 (SiO2/Al2O3 = 38) remained approximately 100% for 405 min at 25 °C, and then the ethylene conversion gradually decreased to zero in the following 450 min. It is revealed that Brønsted acid sites are the C2H4 adsorption sites and the inhibition of C2H4 adsorption sites by H2O vapor is one of the crucial reasons of the activity loss for ethylene oxidation. H2O adsorption-desorption kinetics results demonstrate that slow adsorption and fast desorption characters of H2O on Ag/ZSM-5 with SiO2/Al2O3 ratio of 38 contribute to its good catalytic stability for ethylene oxidation. Taking into account the elucidation of the negative effect of H2O adsorption on Brønsted acid sites on the catalytic stability of Ag/ZSM-5 catalysts for ethylene oxidation, this work will provide new insights into designing high-performance catalysts for ethylene elimination at room temperature.
This study presents detailed experimental and theoretical investigation of manganese-based metal oxides, MnMOx (M: Fe, Ni, Cu) as potential catalysts for the low-temperature toluene oxidation. The ...first part of the paper deals with the detailed characterization of the prepared catalysts and testing of their catalytic activity and stability in the fixed-bed reactor. The MnFeOx exhibited superior and stable catalytic activity for toluene oxidation (T90 = 419–446 K), comparable with the activity of the commercial Pt–Al2O3 catalyst (T90 = 393–423 K). Among the studied catalysts the following order of catalytic activity was determined: MnFeOx > MnNiOx ≈ MnCuOx > MnOx. The one-dimensional (1D) pseudo-homogeneous model was applied to describe behavior of the fixed bed reactor for the low temperature toluene oxidation over prepared MnFeOx catalysts. The second part of the paper is focused on theoretical investigation of toluene interaction on the surface of the single metal oxides (Mn2O3, MnO2, Fe2O3, NiO and CuO) in the oxygen atmosphere using the ReaxFF method, since they were individual dominant phases in the prepared catalysts. A good correlation between the predicted binding energy of toluene adsorption on the surface of studied metal oxide phases and experimentally determined catalytic activities was observed.
Oxygen vacancy defect (OVD) engineering has been recognized as an effective strategy to prepare high-performance catalysts for the oxidation of volatile organic compounds (VOCs) because the generated ...oxygen-deficient sites can lead to an unbalanced electronic structure, resulting in rapid electron transfer, reducing the reaction temperature. Herein, the latest technologies used to increase the OVDs on the catalysts have been introduced and discussed based on the possible catalytic oxidation mechanism, especially the relationship between OVD and catalytic activity for gaseous VOC oxidation. Four approaches to generate OVDs have been summarized: (i) Control over the synthesis and/or calcination temperature, (ii) atom substitution (isovalent-substitution and aliovalent-substitution), (iii) surface modification (noble metal doping and transition metal doping), and (iv) in situ surface treatment (chemical etching and surface reduction). The novel and advanced characterization methods (HRTEM, STM, XPS, Raman, EPR, PALS, EELS, and XAFS) used to understand the existence of OVDs have been summarized. Furthermore, the potential future research on OVD engineering based on amorphous structure generation has been discussed. This review is expected to provide guidance for the design and fabrication of more effective catalysts used for VOC oxidation at lower temperatures.
