Rich surface Co(iii) ions-enhanced Co nanocatalyst benzene/toluene oxidation performance derived from Co(II)Co(III) layered double hydroxide

Investigation of catalytic methane oxidation over Ag/Co2MOx (M = Co, Ni, Cu) catalysts with varying interfacial electron transfer

Atom-doped Co3O4 catalysts loaded with Ag were examined as cost-effective catalysts for methane oxidation. The synthesized Ag/Co2NiOx catalysts exhibited distinctive surface characteristics in contrast with Ag/Co3O4 and Ag/Co2CuOx catalysts prepared using a similar method. Characterization results unveiled that Ag/Co2NiOx featured a higher presence of active surface oxygen species, lattice defects, a larger surface area, and enhanced reducibility. A methane oxidation catalytic performance followed the sequence: Ag/Co2NiOx > Ag/Co3O4 > Ag/Co2CuOx. The investigation delved into methane degradation pathways on the surfaces of three catalysts, examining their behavior under both aerobic and anaerobic atmospheres through in-situ DRIFTS analysis. Furthermore, introducing Ag showed a marked positive effect on Co-Ni mixed oxide, inducing electron transfer and a more active electron system, whereas it exhibited an inverse impact within the surface of Co-Cu mixed oxide. This work provides innovative perspectives on the development of forthcoming environmental catalysts.

Preparation of three-dimensional ordered macroporous Ag/LaFeO3 and heterogeneous photo-Fenton degradation of penicillin G potassium

3DOMLaFeO3 was prepared by template method combined with sol-gel method using monodisperse polystyrene (PS) microspheres as template, and Ag/3DOMLaFeO3 perovskite catalyst was prepared by impregnation method combined with sodium borohydride reduction method. The catalysts were characterised by means of TG, XRD, SEM, BET, XPS, UV-vis DRS, etc. The photo-Fenton catalytic performance, stability and catalytic reaction mechanism of Ag/3DOMLaFeO3 were studied with penicillin G potassium (PEN G) as the model pollutant. The results indicated that the as-prepared Ag/3DOMLaFeO3 exhibited a three-dimensional ordered macroporous (3DOM) structure, and the light capture and mass transfer were enhanced through abundant pores and large specific surface area. Based on the surface plasmon resonance effect (SPR), Ag loading enhanced the absorption of the material in the visible light region, and inhibited the recombination of photogenerated carriers, which improved the photocatalytic performance of 3DOMLaFeO3 under visible light. Under the conditions of hydrogen peroxide dosage of 1.5 mL·L-1, initial pH of 5, PEN G initial concentration of 100 mg·L-1, catalyst dosage of 300 mg·L-1, xenon lamp irradiation, the degration ratio of PEN G and the removal rate of TOC reached 99.99% and 85.45% within 120 min, respectively. In addition, it had a wide range of pH application, excellent stability and practical application value. The quenching experiment and ESR test showed that ·OH and ·O2- were the reasons for high catalytic degradation. The least square method was used to fit the experimental data, and the results displayed that the degradation of PEN G was approximately in line with the first-order kinetic reaction.

Al-Incorporated Cobalt-Layered Double Hydroxides for Enhanced Oxygen Evolution through Morphology and Electronic Structure Regulation

Layered double hydroxides (LDHs) are promising electrocatalytic materials for the oxygen evolution reaction (OER) due to their tunable composition and low cost. Here, we construct ultrathin Al-incorporated Co LDH nanosheets on carbon cloth (CC) by a facile hydrothermal strategy. Compared to Co LDH/CC, the optimized Co₂Al₁ LDH/CC displays significantly improved OER performance, characterized by low overpotentials of only 171 and 200 mV to reach current densities of 10 mA cm^-2 in alkaline and neutral media, respectively, as well as good stability over an extended period. The introduced Al³⁺ and CC support play a synergistic role in steering the morphology of Co₂Al₁ LDH/CC while also increasing the electrochemical active sites. X-ray absorption fine spectra (XAFS) analyses uncover the critical role of Al in regulating the coordination environment of Co atoms, with evidence affording highly active Co oxidation states. Moreover, density functional theory (DFT) calculations confirmed that the Al³⁺ incorporated into Co LDH/CC can efficaciously modulate the electronic density of states of the d-band center of Co atoms, optimize the Gibbs free energies of intermediates toward OER, and thus accelerate the O₂ evolution rate.

Enhanced CO oxidation with cobalt-impregnated porous single-crystal manganese oxides

In this work, Mn2O3, Mn3O4 and MnO single crystals are prepared by using MnCO3 as the precursor. In addition, Co element is loaded on the three manganese oxide single crystals for the CO oxidation reaction.

Non-thermal plasma-enhanced catalytic activation of Mn-Zr-La/Al2O3 catalyst for meta-xylene degradation: Synergetic effects and degradation mechanism

The LaMnO₃ catalysts doped with transition metal (Zr, Co, Fe) were prepared. The influencing factors (the catalyst type, the initial concentration, the gas flow, and oxygen content) on the degradation efficiency by the non-thermal plasma synergistic the LaMnO₃ catalysts doped with Zr, Co and Fe were investigated systematically. The degradation mechanism of the meta-xylene degradation by the non-thermal plasma synergistic Mn-Zr-La/Al₂O₃ was researched. The results showed that the Mn-Zr-La/Al₂O₃ catalyst in the four catalysts had the best degradation efficiency for meta-xylene, which was 99.6% at the applied voltage of 44 kV. The by-product ozone concentration was low, and the NO_x was not detected. Meanwhile, the XPS characterization analysis study revealed that the proportion of Mn⁴⁺ element and the proportion of O_sur in the Zr-doped Mn-Zr-La/Al₂O₃ catalyst were both the highest. The degradation efficiency decreased with the increasing of the initial concentration and gas flow, but first increased and then decreased with the increasing of oxygen content. The fresh and used Mn-Zr-La/Al₂O₃ were characterized by SEM, XRD, BET, FT-IR, O₂-TPD, and the tail gas was treated by GC-MS. Then synergistic degradation mechanism for the meta-xylene by the non-thermal plasma over the Mn-Zr-La/Al₂O₃ catalyst are proposed.

N-doped CoAl oxides from hydrotalcites with enhanced oxygen vacancies for excellent low-temperature propane oxidation

A series of nitrogen-doped CoAlO (N-CoAlO) were constructed by a hydrothermal route combined with a controllable NH₃ treatment strategy. The effects of NH₃ treatment on the physico-chemical properties and oxidation activities of N-CoAlO catalysts were investigated. In comparison to CoAlO, a smallest content decrease in surface Co³⁺ (serving as active sites) while a largest increased amount of surface Co²⁺ (contributing to oxygen species) are obtained over N-CoAlO/4h among the N-CoAlO catalysts. Meanwhile, a maximum N doping is found over N-CoAlO/4h. As a result, N-CoAlO/4h (under NH₃ treatment at 400°C for 4 hr) with rich oxygen vacancies shows optimal catalytic activity, with a T₉₀ (the temperature required to reach a 90% conversion of propane) at 266°C. The more oxygen vacancies are caused by the co-operative effects of N doping and suitable reduction of Co³⁺ for N-CoAlO/4h, leading to an enhanced oxygen mobility, which in turn promotes C₃H₈ total oxidation activity dominated by Langmuir-Hinshelwood mechanism. Moreover, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) analysis shows that N doping facilities the decomposition of intermediate species (propylene and formate) into CO₂ over the catalyst surface of N-CoAlO/4h more easily. Our reported design in this work will provide a promising way to develop abundant oxygen vacancies of Co-based catalysts derived from hydrotalcites by a simple NH₃ treatment.

Solution combustion derived oxygen vacancy-rich Co3O4 catalysts for catalytic formaldehyde oxidation at room temperature

Fabricating abundant oxygen vacancies is crucial for non-noble metal oxides to catalyze formaldehyde (HCHO) oxidation at room temperature. Here, a simple one-pot preparation method via solution combustion was found to produce oxygen vacancy-rich Co₃O₄ catalysts, avoiding delicate defect engineering. The catalyst was evaluated to result in 52% HCHO conversion in a dynamic flow reaction with ∼6 ppm HCHO, which was higher as compared to some other Co₃O₄ catalysts prepared in three methods of sol–gel, deposition precipitation and thermal decomposition. The optimal catalyst also exhibited high durability with steady HCHO conversion (∼47%) for more than 50 h. The catalyst characterizations revealed that the explosive solution combustion brought out two particular features of Co₃O₄, namely, the porous network structure with nano-holes and the abundant oxygen vacancies. The latter was demonstrated to increase the reactive oxygen species and to improve the reducibility and the oxygen transport capacity of Co₃O₄. The two features and the derived properties are beneficial to the activity and durability of Co₃O₄. The solution combustion method can serve as a simple and feasible way to fabricate abundant oxygen vacancies to provide room-temperature activity of Co₃O₄ for HCHO elimination at room temperature.

The rich oxygen vacancies in porous Co₃O₄ were generated in solution combustion, offering high room-temperature activity for formaldehyde oxidation.

Synergistic effects in Mn-Co mixed oxide supported on cordierite honeycomb for catalytic deep oxidation of VOCs

A series of Co-Mn mixed oxide catalyst supported on a cordierite monolith was facilely synthesized by ultrasonic impregnation. Its catalytic performance was evaluated in the combustion of toluene, ethyl acetate and its mixture. It was observed that with incorporating Mn into Co₃O₄, the formation of solid solution with spinel structure could significantly improve the catalytic activity of pure phase Co₃O₄. And the monolithic Co_0.67Mn_0.33O_x catalyst showed the best catalytic performance in the catalytic oxidation of toluene and ethyl acetate which could be completely oxidized at 220 and 180°C respectively under the reaction velocity (WHSV) about 45,000 mL/(g•hr) and pollutant concentration of 500 ppmV. The total conversion temperature of the VOCs mixture was at 230°C (500 ppmV toluene and 500 ppmV ethyl acetate) and determined by the temperature at which the most difficult molecule was oxidized. The excellent catalytic performance of monolithic Co_0.67Mn_0.33O_x was attributed to the higher content of Mn³⁺, Co³⁺, surface adsorbed oxygen and better redox ability. The prepared catalyst showed the good mechanical stability, reaction stability, and good adaptability to different reaction conditions.

Metal-organic frameworks-derived hierarchical Co3O4/CoNi-layered double oxides nanocages with the enhanced catalytic activity for toluene oxidation

The development of active transition-metal oxide (TMO) catalysts for the abatement of volatile organic compounds (VOCs) remains a great challenge. Controllable synthesis of TMOs with specific morphology and suitable composition is a promising way for acquiring efficient oxidation catalysts. Herein, a series of hierarchical Co₃O₄/CoNi-layered double oxides (CoNi-LDO) nanocages covered by interlaced nanosheets were synthesized using a cobalt metal-organic framework (Co-MOF)-based strategy. The textural properties, morphology, surface chemical state, and reducibility of the CoNi-LDO catalysts were systematically characterized by various techniques. The catalytic activity toward toluene oxidation and the stability performance was investigated. Results demonstrated that the morphology, composition, and textual properties can be controlled by tuning the post-synthetic etching reaction conditions. Benefiting from the structural and compositional merits, as well as the superior low-temperature reducibility, the CoNi-LDO-1 catalyst (Ni/Co molar ratio was 0.39) with core-shell structure exhibited excellent activity toward toluene oxidation. Our work offers a new strategy for the design of high-performance oxidation catalysts for the abatement of VOCs.

Understanding the Evolution of Cobalt-Based Metal-Organic Frameworks in Electrocatalysis for the Oxygen Evolution Reaction

Metal-organic frameworks (MOFs) have attracted increasing attention as a promising electrode material for the oxygen evolution reaction (OER). Comprehending catalytic mechanisms in the OER process is of key relevance for the design of efficient catalysts. In this study, two types of Co based MOF with different organic ligands (ZIF-67 and CoBDC; BDC=1,4-benzenedicarboxylate) are synthesized as OER electrocatalysts and their electrochemical behavior is studied in alkaline solution. Physical characterization indicates that ZIF-67, with tetrahedral Co sites, transforms into α-Co(OH)₂ on electrochemical activation, which provides continuous active sites in the following oxidation, whereas CoBDC, with octahedral sites, evolves into β-Co(OH)₂ through hydrolysis, which is inert for the OER. Electrochemical characterization reveals that Co sites coordinated by nitrogen from imidazole ligands (Co-N coordination) are more inclined to electrochemical activation than Co-O sites. The successive exposure and accumulation of real active sites is responsible for the gradual increase in activity of ZIF-67 in OER. This work not only indicates that CoMOFs are promising OER electrocatalysts but also provides a reference system to understand how metal coordination in MOFs affects the OER process.

Effect of Cr doping in promoting the catalytic oxidation of dichloromethane (CH2Cl2) over Cr-Co@Z catalysts

A core-shell catalyst which consists of a Co₃O₄ core and ZSM-5 shell, was prepared by microwave hydrothermal method and subjected for dichloromethane (DCM) oxidation. Chromium, cerium, niobium, and manganese species were separately introduced into the core-shell catalyst using the wet precipitation method and denoted as M-Co@Z (M = Cr, Ce, Nb, Mn). The catalytic activity of the Cr-Co@Z catalyst was significantly increased due to the interaction between Cr₂O₃ and Co₃O₄. The results of Raman spectra indicated the incorporation of chromium into the Co₃O₄ lattice and revealed the existence of the interaction between Cr₂O₃ and Co₃O₄. The synergistic effect between Cr₂O₃ and Co₃O₄ might be conducive to the generation of highly defective structure and increase the ratio of Co³⁺/Co²⁺ of the sample, leading to its better oxygen mobility. The dechlorination ability of Cr-Co@Z was also promoted due to the enhanced mobility of lattice oxygen. Based on in situ DRIFT studies, a possible reaction route of CH₂Cl₂ oxidation over Cr-Co@Z catalyst was proposed.

Facile Synthesis of Two-Dimensional Iron/Cobalt Metal-Organic Framework for Efficient Oxygen Evolution Electrocatalysis

A facile synthesis is reported of two-dimensional (2D) bimetallic (Fe/Co=1:2) metal-organic frameworks (MOF, ca. 2.2 nm thick) via simple stirring of the reaction mixture of Fe/Co salts and 1,4-benzene dicarboxylic acid (1,4-BDC) in the presence of triethylamine and water at room temperature. The mechanism of the 2D, rather than bulk, MOF was revealed by studying the role of each component in the reaction mixture. It was found that these 2D MOF-Fe/Co(1:2) exhibited excellent electrocatalytic activity for the oxygen evolution reaction (OER) under basic conditions. The electrocatalytic mechanism was disclosed via both experimental results and density functional theory (DFT) calculation. The 2D morphology and co-doping of Fe/Co contributed to the superior OER performance of the 2D MOF-Fe/Co(1:2). The simple and efficient synthetic method is suitable for the mass production and future commercialization of functional 2D MOF with low cost and high yield.

Bimetal oxide CuO/Co3O4 derived from Cu ions partly-substituted framework of ZIF-67 for toluene catalytic oxidation

A MOF-templated method is developed to prepare bimetal oxide CuO/Co₃O₄ by in situ pyrolysis of Cu²⁺ partly-substituted ZIF-67 precursor. The physicochemical properties of CuO/Co₃O₄ are studied by various characterizations such as X-ray diffraction, Raman analysis, transmission electron microscope, scanning electron microscope, N₂ adsorption-desorption measurement, X-ray photoelectron spectroscope, O₂ temperature-programmed desorption, H₂ temperature-programmed reduction, etc. Comparison with CuO, Co₃O₄ and Mix-CuO/Co₃O₄, 90 % of both toluene conversion and mineralization over CuO/Co₃O₄ are fulfilled at around 229 °C under the condition of 1000 ppm toluene and weight hour space velocity =20,000 mL/(g h), which is promoted more than 40 °C. The better catalytic performance of CuO/Co₃O₄ attributes to high mutual dispersion of two oxides, porous structure, lower temperature reducibility, abundant lattice defects, more active oxygen species, higher Co³⁺/Co²⁺ and O_latt/O_ads molar ratios. Meanwhile, CuO/Co₃O₄ exhibits a better catalytic stability at different conversions and a good tolerance to 10 vol.% of water vapour. The investigation of temperature-dependent active oxygen species and in-situ DRIFTS results reveal that toluene oxidation on CuO/Co₃O₄ obeys Mars van Krevelen mechanism.

Bimetallic Pt-Co Nanoparticle Deposited on Alumina for Simultaneous CO and Toluene Oxidation in the Presence of Moisture

Carbon monoxide (CO) and hydrocarbons (HCs) generally have competitive adsorption on the active site of noble-metal nano-catalysts, thus developing an effective way to reduce the passivation of competitive reaction with each other is an urgent problem. In this study, we successfully synthesized transition metal-noble metal (Pt-M) alloys via introducing inexpensive metal elements (M = Ni, Co and Cu) into Pt particles and then deposited on alumina support to form Pt-based catalysts. Subsequently, we choose CO and toluene as polluting gases to evaluate the catalytic activities of Pt-M/Al2O3 catalysts. Introducing inexpensive metal elements (M = Ni, Co, and Cu) significantly changed the physicochemical properties and catalytic activities of these Pt-based catalysts. It can be found that the Pt-Co/Al2O3 catalyst exhibited outstanding catalytic activity for CO and toluene oxidation under mixed gas atmosphere, compared with other Pt-based catalysts, which is due to the higher dispersity, more surface adsorption oxygen, and well redox ability. Surprisingly, H2O could promote the catalytic activities for CO/toluene co-oxidation over the Pt-Co/Al2O3 catalyst. Thus, the present synthetic strategy not only opens an avenue towards the synthesis of noble metal-based catalysts, but also provides an excellent tolerance to H2O in the catalytic process.

Enhancement of catalytic toluene combustion over Pt-Co3O4 catalyst through in-situ metal-organic template conversion

A Pt-Co₃O₄ catalyst named Pt-Co(OH)₂-O was prepared by metal-organic templates (MOTs) conversion and used for catalytic oxidation of toluene. Through the conversion, the morphology of catalysts transformed from rhombic dodecahedron to nanosheet and the coated Pt nanoparticles (NPs) were more exposed. The Binding energy shift in XPS test indicates that the strong metal-support strong interaction (SMSI) has enhanced, and the physicochemical changes caused by it are characterized by other techniques. At the same time, Pt-Co(OH)₂-O showed the best catalytic performance (T₅₀ = 157 °C, T₉₀ = 167 °C, E_a = 40.85 kJ mol^-1, TOF_Pt = 2.68 × 10^-3 s^-1) and good stability. In addition, the in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) studies have shown that because SMSI weakened the Co-O bond, the introduction of Pt NPs can make the migration of oxygen in the catalyst easier. The change of binding energy change and the content of various species in the quasi in situ XPS experiment further confirmed that the Pt-Co(OH)₂-O catalyst has stronger SMSI, resulting in its stronger electron transfer ability and oxygen migration ability, which is conducive to catalytic reactions. This work provides new ideas for the development of supported catalysts and provides a theoretical reference for the relevant verification of SMSI.

Preparation of MnO2 decorated Co3Fe1Ox powder/monolithic catalyst with improved catalytic activity for toluene oxidation

In this paper, KMnO₄ was used to pre-treat Co₃Fe-layered double hydroxides (LDH) precursor to prepare MnO₂ decorated Co₃Fe₁O_x catalyst. The toluene oxidation performance of the catalyst was investigated systematically. The optimized 0.1MnCF-LDO catalyst exhibited the best catalytic performance, and the temperatures of 50% and 90% toluene conversion (T₅₀ and T₉₀) were 218 and 243°C, respectively. The apparent activation energy (E_a) was 31.6 kJ/mol. The characterization results showed that the pre-redox reaction by KMnO₄ could increase the specific surface area, Co³⁺ species amount and oxygen defect concentration of the catalyst, which are the main reason of the improved toluene catalytic activity. Besides, this method was also applied to enhance toluene oxidation of iron mesh based monolithic catalyst. The 0.1MnCF-LDO/Iron mesh (IM) catalyst showed a 90% toluene conversion at around 316°C which was much lower than that of without MnO₂ addition (359°C). In addition, the water resistant of all the catalysts was studied as well, all the samples showed relatively good water resistance. The toluene conversion still remained to be over >80% even in the presence of 10 vol.% water vapor.

A Lamellar MWW Zeolite With Silicon and Niobium Oxide Pillars: A Catalyst for the Oxidation of Volatile Organic Compounds

In this work, an MWW-type zeolite with pillars containing silicon and niobium oxide was synthesized to obtain a hierarchical zeolite. The effect of niobium insertion in the pillaring process was determined by combining a controllable acidity and accessibility in the final material. All pillared materials had niobium occupying framework positions in pillars and extra-framework positions. The pillared material, Pil-Nb-4.5 with 4.5 wt % niobium, did not compromise the mesoporosity formed by pillaring, while the increase of niobium in the structure gradually decreased the mesoporosity and ordering of lamellar stacking. The morphology of the pillared zeolites and the niobium content were found to directly affect the catalytic activity. Specifically, we report on the activity of the MWW-type zeolites with niobium catalyzing the gas-phase oxidation of volatile organic compounds (VOCs), which is an important reaction for clean environmental. All produced MWW-type zeolites with niobium were catalytically active, even at low temperatures and low niobium loading, and provided excellent conversion efficiencies.

Toluene oxidation over Co3+-rich spinel Co3O4: Evaluation of chemical and by-product species identified by in situ DRIFTS combined with PTR-TOF-MS

Series of Co³⁺-rich spinel Co₃O₄ catalysts were synthesized and evaluated by toluene catalytic oxidation. An outstanding activity was achieved over Co₃O₄-N utilizing Co(NO₃)₂·6H₂O as precursor (T₅₀ = 211 °C, T₉₀ = 217 °C at conditions: 1000 ppm(v), WHSV = 60 000 mL g^-1 h^-1). Results of comparative characterizations demonstrated that such excellent performance was mainly attributed to large surface area, high reducibility at low temperature, high abundance of Co³⁺ ions and structure defects, as well as highly active surface oxygen. The results of in situ DRIFTS revealed that in the air or N₂ atmosphere, the by-products were almost the same. The reaction pathway of toluene oxidation can be described as follow: transformation of toluene from benzyl alcohol, benzaldehyde, benzoate, benzene, phenol, benzoquinone, maleic acid and to final products, which were fully confirmed by PTR-TOF-MS. Besides, ring opened by-products, such as acetone, acetic acid, acetaldehyde, etc. were also detected. In this work, the combination of in situ DRIFTS and PTR-TOF-MS provided a promising approach for further understanding of the mechanism of VOCs elimination.

Macroscopic Hexagonal Co3O4 Tubes Derived from Controllable Two-Dimensional Metal-Organic Layer Single Crystals: Formation Mechanism and Catalytic Activity

Macroscopic Co₃O₄ hexagonal tubes were successfully synthesized using hollow two-dimensional (2D) MOL (metal-organic layer) single crystals as sacrificial templates. The hollow 2D MOL single crystals were prepared under hydrothermal conditions with acetonitrile (MeCN) as an interference agent. The formation of hollow-structured 2D MOL single crystals was tracked by time-dependent experiments, and two simultaneous paths-namely, the crystal-to-crystal transformation in solution and the dissolution + migration (toward the external surface) of inner crystallites-were identified as playing a key role in the formation of the unique hollow structure. The calculated change in Gibbs free energy (ΔG = -1.18 eV) indicated that the crystal-to-crystal transformation was spontaneous at 393 K. Further addition of MeCN as an interference agent eventually leads to the formation of macroscopic hexagonal tubes. Among all of the as-synthesized Co₃O₄, Co-MeCN-O with a hexagonal tube morphology exhibited the best catalytic performance in toluene oxidation, it achieved a toluene conversion of 90% (T₉₀) at ∼227 °C (a space velocity of 60 000 mL g^-1 h^-1) and the activity energy (E_a) is 69.5 kJ mol^-1. A series of characterizations were performed to investigate the structure-activity correlation. It was found that there are more structure defects, more adsorbed surface oxygen species, more surface Co³⁺ species, and higher reducibility at low temperatures on the Co-MeCN-O than on other Co₃O₄ samples; these factors are responsible for its excellent catalytic performance. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) characterization showed that, when there is no oxygen in the atmosphere, the lattice oxygen may be involved in the activation of toluene, and the gas-phase oxygen replenished by the oxygen vacancies was essential for the total oxidation of toluene on the surface of the Co-MeCN-O catalysts, it also proves the importance of oxygen vacancies. Moreover, for the Co-MeCN-O catalysts, no obvious decrease in catalytic performance was observed after 120 h at 220 °C and it is still stable after cycling tests, which indicates that it exhibits excellent stability for toluene oxidation. This study sheds lights on the controllable synthesis of macroporous-microporous materials in single-crystalline form without an external template, and, thus, it may serve as a reference for future design and synthesis of hollow porous materials with outstanding catalytic performance.

Self-Templating Synthesis of 3D Hierarchical NiCo2O4@NiO Nanocage from Hydrotalcites for Toluene Oxidation

Rational design LDHs (layered double hydroxides) with 3D hierarchical hollow structures have generated widespread interest for catalytic oxidation due to the high complexity in shell architecture and composition. Herein, we reported a handy two-step method to construct a 3D hierarchical NiCo2O4/NiO nanocage. This synthetic strategy contains a partial in situ transformation of ZIF-67 (zeolitic imidazolate framework-67) into Co-NiLDH yolk-shelled structures following ethanol etching, and a structure-preserved transformation from Co-NiLDH@ZIF-67 to a biphase nanocage following calcination. CoNi-yh-T (varied reaction time and calcination temperature) nanocages were investigated systematically by Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS), H2- temperature-programmed reduction (TPR), NH3-temperature-programmed desorption (TPD) and studied for toluene oxidation. The CoNi-6h-350 sample showed much higher activity with 90% toluene conversion (T90) at 229 °C at a high space velocity (SV = 60,000 mL g−1 h−1) than other catalysts (T90 >240 °C). Abundant surface high valence Co ions caused by the novel hierarchical nanostructures, together with adsorbed oxygen species and abundant medium-strength surface acid sites, played a key role for catalytic activities.

Leaf-like Co-ZIF-L derivatives embedded on Co2AlO4/Ni foam from hydrotalcites as monolithic catalysts for toluene abatement

Herein, a series of distinctively monolithic catalysts were first synthesized by decorating leaf-like Co-ZIF-L derivatives on Co₂AlO₄ coral-like microspheres from CoAl layered double hydroxides (LDHs), which were coated on three-dimensional porous Ni foam. As a proof of concept application, toluene was chosen as a probe molecule to evaluate their catalytic performances over the as-synthesized catalysts. As a result, the L-12 sample derived from Co₂AlO₄@Co-Co LDHs displayed an excellent catalytic performance, cycling stability and long-term stability for toluene oxidation (T₉₉ = 272 °C, 33 °C lower than that of Co₂AlO₄ sample), where leaf-like Co-ZIF-L served as a sacrificial template to synthesize Co-Co LDHs. The improved catalytic performance was attributed to its distinctive structure, in which leaf-like Co-ZIF-L derivatives on Co₂AlO₄ resulted in its higher specific surface area, lower-temperature reducibility, rich surface oxygen vacancy and high valence Co³⁺ species. This work thus demonstrates a feasible strategy for the design and fabrication of hybrid LDHs/ZIFs-derived composite architectures, which is expected to construct other novel monolithic catalysts with hierarchical structures for other potential applications.

Co3O4-CuCoO2 Nanomesh: An Interface-Enhanced Substrate that Simultaneously Promotes CO Adsorption and O2 Activation in H2 Purification

Nanomaterials are widely used as redox-type reaction catalysts, while reactant adsorption and O₂ activation are hardly to be promoted simultaneously, restricting their applications in many important catalytic fields such as preferential CO oxidation (CO-PROX) in H₂-rich stream. In this work, an interface-enhanced Co₃O₄-CuCoO₂ nanomesh was initially synthesized by a hydrothermal process using aluminum powder as a sacrificial agent. This nanomesh is systematically characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N₂ adsorption, X-ray photoelectron spectroscopy, UV-vis absorption spectroscopy, Raman spectroscopy, X-ray absorption near-edge spectroscopy, hydrogen temperature-programmed reduction, and oxygen temperature-programmed desorption. It is demonstrated that the nanomesh possesses high-density nanopores, enabling a large number of CO adsorption sites exposed to the surface. Meanwhile, electron transfer from O^2- to Co³⁺/Co²⁺ and the weakened bonding strength of Co-O bond at surfaces promoted the oxygen activation and redox ability of Co₃O₄. When tested as a catalyst for CO-PROX, this nanomesh with an optimized pore structure and a surface electronic structure, exhibits a strikingly high catalytic oxidation activity at low temperatures as well as a broader operation temperature window (i.e., CO conversion >99.0%, 100-200 °C) in the CO selective oxidation reaction. The present finding should be highly useful in promoting the quest for better CO-PROX catalysts, a hot topic for proton exchange membrane fuel cells and automotive vehicles.

Macroporous Ni foam-supported Co3O4 nanobrush and nanomace hybrid arrays for high-efficiency CO oxidation

Herein, we reported the synthesis of well-defined Co₃O₄ nanoarrays (NAs) supported on a monolithic three-dimensional macroporous nickel (Ni) foam substrate for use in high-efficiency CO oxidation. The monolithic Co₃O₄ NAs catalysts were obtained through a generic hydrothermal synthesis route with subsequent calcination. By controlling the reaction time, solvent polarity and deposition agent, these Co₃O₄ NAs catalysts exhibited various novel morphologies (single or hybrid arrays), whose physicochemical properties were further characterized by using several analytical techniques. Based on the catalytic and characterization analyses, it was found that the Co₃O₄ NAs-6 catalyst with nanobrush and nanomace arrays displayed enhanced catalytic activity for CO oxidation, achieving an efficient 100% CO oxidation conversion at a gas hourly space velocity (GHSV) 10,000hr^-1 and 150°C with long-term stability. Compared with the other Co₃O₄ NAs catalysts, it had the highest abundance of surface-adsorbed oxygen species, excellent low-temperature reducibility and was rich in surface-active sites (Co³⁺/Co²⁺=1.26).