Promoting Effects of In2O3 on Co3O4 for CO Oxidation: Tuning O2 Activation and CO Adsorption Strength Simultaneously

Pt-Embedded-Co3O4 hollow structure as a highly efficient catalyst for toluene combustion

Pt embedded Co₃O₄ hollow structure nanocomposites (Pt@Co₃O₄) were facilely prepared through metal–organic frameworks (MOFs) sacrificial strategy. Compared with Pt/Co₃O₄ and bare Co₃O₄ catalyst, it shows excellent toluene combustion performance.

Enhancement of propane combustion activity over CoOx catalysts by introducing C2–C5 diols

C₂–C₅ diols effectively promote the degradation of propane by weakening the Co–O bond strength of CoO_x.

Construction of defective cobalt oxide for methane combustion by oxygen vacancy engineering

Defects are pivotal to endow metal oxide catalysts with an efficient catalytic oxidation ability.

Porous hexagonal nanoplate cobalt oxide derived from a coordination polymer as an effective catalyst for activating Oxone in water

As cobalt (Co) represents an effective transition metal for activating Oxone to degrade contaminants, tricobalt tetraoxide (Co₃O₄) is extensively employed as a heterogeneous phase of Co for Oxone activation. Since Co₃O₄ can be manipulated to exhibit various shapes, 2-dimensional plate-like morphology of Co₃O₄ can offer large contact surfaces. If the large plate-like surfaces can be even porous, forming porous nanoplate Co₃O₄ (PNC), such a PNC should be a promising catalyst for Oxone activation. Therefore, a facile but straightforward method is proposed to prepare such a PNC for activating Oxone to degrade pollutants. In particular, a cobaltic coordination polymer with a morphology of hexagonal nanoplate, which is synthesized through coordination between Co²⁺ and thiocyanuric acid (TCA), is adopted as a precursor. Through calcination, CoTCA could be transformed into hexagonal nanoplate-like Co₃O₄ with pores to become PNC. This PNC also shows different characteristics from the commercial Co₃O₄ nanoparticle (NP) in terms of surficial reactivity and textural properties. Thus, PNC exhibits a much higher catalytic activity than the commercial Co₃O₄ NP towards activation of Oxone to degrade a model contaminant, salicylic acid (SA). Specifically, SA was 100% degraded by PNC activating Oxone within 120 min, and the E_a of SA degradation by PNC-activated Oxone is 70.2 kJ/mol. PNC can also remain stable and effective for SA degradation even in the presence of other anions, and PNC could be reused over multiple cycles without significant loss of catalytic activity. These features validate that PNC is a promising and useful Co-based catalyst for Oxone activation.

Crystal Facet Induced Single-Atom Pd/Cox Oy on a Tunable Metal-Support Interface for Low Temperature Catalytic Oxidation

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 Co_x O_y 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.

Comparison of Different Metal Doping Effects on Co3O4 Catalysts for the Total Oxidation of Toluene and Propane

Metal-doped (Mn, Cu, Ni, and Fe) cobalt oxides were prepared by a coprecipitation method and were used as catalysts for the total oxidation of toluene and propane. The metal-doped catalysts displayed the same cubic spinel Co3O4 structure as the pure cobalt oxide did; the variation of cell parameter demonstrated the incorporation of dopants into the cobalt oxide lattice. FTIR spectra revealed the segregation of manganese oxide and iron oxide. The addition of dopant greatly influenced the crystallite size, strain, specific surface area, reducibility, and subsequently the catalytic performance of cobalt oxides. The catalytic activity of new materials was closely related to the nature of the dopant and the type of hydrocarbons. The doping of Mn, Ni, and Cu favored the combustion of toluene, with the Mn-doped one being the most active (14.6 × 10−8 mol gCo−1 s−1 at 210 °C; T50 = 224 °C), while the presence of Fe in Co3O4 inhibited its toluene activity. Regarding the combustion of propane, the introduction of Cu, Ni, and Fe had a negative effect on propane oxidation, while the presence of Mn in Co3O4 maintained its propane activity (6.1 × 10−8 mol gCo−1 s−1 at 160 °C; T50 = 201 °C). The excellent performance of Mn-doped Co3O4 could be attributed to the small grain size, high degree of strain, high surface area, and strong interaction between Mn and Co. Moreover, the presence of 4.4 vol.% H2O badly suppressed the activity of metal-doped catalysts for propane oxidation, among them, Fe-doped Co3O4 showed the best durability for wet propane combustion.

Topological transformation of LDH nanosheets to highly dispersed PtNiFe nanoalloys enhancing CO oxidation performance

Highly dispersed nanoalloys with a tailored metal-oxide interface are pivotal in developing advanced catalysts with superior performance for applications. Herein, a series of highly dispersed Pt/NiFeAl nanoalloys on amorphous supports were successfully fabricated by a topological transformation of layered-double-hydroxide nanosheets. With increasing reduction temperature, samples Pt/NiFeAl-x (x = reduction temperature) showed a progressive transformation from Pt/NiFeAl-LDH to a mixture (Pt, NiFe alloys, FeOy, and NiOy) supported on amorphous Al2O3, which eventually transformed to atomically dispersed PtNiFe alloys supported on amorphous Al2O3. Systematic sample characterization demonstrates that amorphous alumina-supported PtNiFe nanoalloys are merited by excellent redox ability, outstanding O2 activation ability, and moderate CO adsorption strength. When tested as catalysts for CO oxidation, all samples have demonstrated an apparent interfacial effect on catalytic performance, among which Pt/NiFeAl-600 shows a strikingly high CO oxidation activity at low-temperatures coupled with a broader operation temperature window (i.e. CO conversion >99.0%, 100-400 °C). Such a topological transformation strategy has proven applicable for generating atomically dispersed nanoalloys on amorphous supports for catalytic applications.

An efficient defect engineering strategy to enhance catalytic performances of Co3O4 nanorods for CO oxidation

Catalytic oxidation of CO at ambient temperature is an important reaction for many environmental applications. Here, we employed a defect engineering strategy to design an extraordinarily effective Sn-doped Co₃O₄ nanorods (NRs) catalyst for CO oxidation. Our combined theoretical and experimental data demonstrated that Co²⁺ in the lattice of Co₃O₄ were substituted by Sn⁴⁺. Based on a variety of characterizations and kinetic studies, this catalyst was found to combine the advantages of the nanorod-like morphology for largely exposing catalytically active Co³⁺ sites and the promotional effect of Sn dopant for adjusting the textural/redox properties. Additionally, the Sn-substituted Co₃O₄ NRs can be further activated via heat treatment to achieve low-temperature CO oxidation (T₁₀₀ ∼ -100 °C) with excellent stability at ambient temperature. This study reveals the importance of Sn-substitution of inactive Co²⁺ in Co₃O₄ and provides an ultra-efficient catalyst for CO oxidation, making this robust material one of the most powerful catalysts available up to now.

Precise design and synthesis of Pd/InOx@CoOx core-shell nanofibers for the highly efficient catalytic combustion of toluene

In this work, Pd/InO_x@CoO_x core-shell nanofibers, CoO_x@Pd/InO_x core-shell nanofibers and Pd/InO_x/CoO_x nanofibers with different morphologies have been successfully synthesized for the catalytic combustion of toluene. Among them, the Pd/InO_x@CoO_x core-shell sample is novel and composed of Pd/InO_x nanotube cores, CoO_x nanocubes and CoO_x nanoparticle shells derived from ZIF-67. On the contrary, the CoO_x@Pd/InO_x core-shell catalyst is assembled by CoO_x nanocube cores and Pd/InO_x nanotube shells. Finally, the Pd/InO_x/CoO_x nanofibers as references are synthesized by a method similar to the synthesis of the CoO_x@Pd/InO_x core-shell sample. Interestingly, the Pd/InO_x@CoO_x core-shell sample displayed the best activity for toluene oxidation with T₉₀ = 253 °C, good thermal stability and good cyclic stability during three runs. Through some characterizations, it was verified that the Pd/InO_x@CoO_x core-shell sample exhibited the best performance for toluene oxidation reactions due to a larger specific surface area, higher reducibility, more abundant structural defects and oxygen vacancies, higher proportion of Pd⁰ and Co³⁺ species and higher lattice oxygen species than others. Simultaneously, the Pd/InO_x@CoO_x core-shell sample exhibited good thermal stability and cyclic stability, which might be due to the layer of the CoO_x shell to protect the stability of the Pd nanoparticle core.

Atomic-Level Dispersion of Bismuth over Co3O4 Nanocrystals—Outstanding Promotional Effect in Catalytic DeN2O

A series of cobalt spinel catalysts doped with bismuth in a broad range of 0–15.4 wt % was prepared by the co-precipitation method. The catalysts were thoroughly characterized by several physicochemical methods (X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), Raman spectroscopy (µRS), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption analyzed with Brunaer-Emmett-Teller theory (N2-BET), work function measurements (WF)), as well as aberration-corrected scanning transmission electron microscopy (STEM) coupled with energy-dispersive X-ray spectroscopy (EDX) and electron energy-loss spectroscopy (EELS). The optimal bismuth promoter content was found to be 6.6 wt %, which remarkably enhanced the performance of the cobalt spinel catalyst, shifting the N2O decomposition (deN2O) temperature window (T50%) down from approximately 400 °C (for Co3O4) to 240 °C (for the 6.6 wt % Bi-Co3O4 catalyst). The high-resolution STEM images revealed that the high activity of the 6.6 wt % Bi-Co3O4 catalyst can be associated with an even, atomic-level dispersion (3.5 at. nm−2) of bismuth over the surface of cobalt spinel nanocrystals. The improvement in catalytic activity was accompanied by an observed increase in the work function. We concluded that Bi promoted mostly the oxygen recombination step of a deN2O reaction, thus demonstrating for the first time the key role of the atomic-level dispersion of a surface promoter in deN2O reactions.

Nano ferrites (AFe2O4, A = Zn, Co, Mn, Cu) as efficient catalysts for catalytic ozonation of toluene

Nano ferrites (AFe₂O₄, A = Zn, Co, Mn, Cu) were supported on the surface of γ-Al₂O₃ by hydrothermal synthesis to prepare a series of novel catalysts (AFe₂O₄/γ-Al₂O₃) for catalytic ozonation of high concentration toluene at ambient temperature.

Tuning effect of amorphous Fe2O3 on Mn3O4 for efficient atom-economic synthesis of imines at low temperature: improving [O] transfer cycle of Mn3+/Mn2+ in Mn3O4

A novel Fe₂O₃ modified Mn₃O₄ catalyst (Fe₅Mn₅-100) has been prepared by adopting a simple co-precipitation method following low temperature baking. Fe₅Mn₅-100 showed exceptionally high catalytic activity for the production of imine.

Defects-Induced In-Plane Heterophase in Cobalt Oxide Nanosheets for Oxygen Evolution Reaction

Cobalt oxides as efficient oxygen evolution reaction (OER) electrocatalysts have received much attention because of their rich reserves and cheap cost. There are two common cobalt oxides, Co₃ O₄ (spinel phase, stable but poor intrinsic activity) and CoO (rocksalt phase, active but easily be oxidatized). Constructing Co₃ O₄ /CoO heterophase can inherit both characteristic features of each component and form a heterophase interface facilitating charge transfer, which is believed to be an effective strategy in designing excellent electrocatalysts. Herein, an atomic arrangement engineering strategy is applied to improve electrocatalytic activity of Co₃ O₄ for the OER. With the presence of oxygen vacancies, cobalt atoms at tetrahedral sites in Co₃ O₄ can more easily diffuse into interstitial octahedral sites to form CoO phase structure as revealed by periodic density functional theory computations. The Co₃ O₄ /CoO spinel/rocksalt heterophase can be in situ fabricated at the atomic scale in plane. The overpotential to reach 10 mA cm^-2 of Co₃ O₄ /CoO is 1.532 V, which is 92 mV smaller than that of Co₃ O₄ . Theoretical calculations confirm that the excellent electrochemical activity is corresponding to a decline in average p-state energy of adsorbed-O on the Co₃ O₄ /CoO heterophase interface. The reaction Gibbs energy barrier has been significantly decreased with the construction of the heterophase interface.

Oxygen Vacancy-rich Porous Co3O4 Nanosheets toward Boosted NO Reduction by CO and CO Oxidation: Insights into the Structure-Activity Relationship and Performance Enhancement Mechanism

Oxygen vacancy-rich porous Co₃O₄ nanosheets (OV-Co₃O₄) with diverse surface oxygen vacancy contents were synthesized via facile surface reduction and applied to NO reduction by CO and CO oxidation. The structure-activity relationship between surface oxygen vacancies and catalytic performance was systematically investigated. By combining Raman, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and O₂-temperature programmed desorption, it was found that the efficient surface reduction leads to the presence of more surface oxygen vacancies and thus distinctly enhance the surface oxygen amount and mobility of OV-Co₃O₄. The electron transfer towards Co sites was promoted by surface oxygen vacancies with higher content. Compared with the pristine porous Co₃O₄ nanosheets, the presence of more surface oxygen vacancies is beneficial for the catalytic performance enhancement for NO reduction by CO and CO oxidation. The OV-Co₃O₄ obtained in 0.05 mol L^-1 NaBH₄ solution (Co₃O₄-0.05) exhibited the best catalytic activity, achieving 100% NO conversion at 175 °C in NO reduction by CO and 100% CO conversion at 100 °C in CO oxidation, respectively. Co₃O₄-0.05 exhibited outstanding catalytic stability and resistance to high gas hour space velocity in both reactions. Combining in situ DRIFTS results, the enhanced performance of OV-Co₃O₄ for NO reduction by CO should be attributed to the promoted formation and transformation of dinitrosyl species and -NCO species at lower and higher temperatures. The enhanced performance of OV-Co₃O₄ for CO oxidation is due to the promotion of oxygen activation ability, surface oxygen mobility, as well as the enhanced CO₂ desorption ability. The results indicate that the direct regulation of surface oxygen vacancies could be an efficient way to evidently enhance the catalytic performance for NO reduction by CO and CO oxidation.

Enhanced Electrocatalytic Performance through Body Enrichment of Co-Based Bimetallic Nanoparticles In Situ Embedded Porous N-Doped Carbon Spheres

Extending available body space loading active species and controllably tailoring the d-band center to Fermi level of catalysts are of paramount importance but extremely challenging for the enhancement of electrocatalytic performance. Herein, a melamine-bridged self-construction strategy is proposed to in situ embed Co-based bimetallic nanoparticles in the body of N-doped porous carbon spheres (CoM-e-PNC), and achieve the controllable tailoring of the d-band center position by alloying of Co and another transition metal M (M = Ni, Fe, Mn, and Cu). The enrichment and exposure of the active sites in the body interior of porous carbon spheres, and the best balance between the adsorption of OH species and the desorption of O₂ induced by optimizing the d-band center position, collectively enhance the oxygen evolution reaction (OER) performance. Meanwhile, the relationship of d-band center position and OER activity is found to exhibit the volcano curve rule, where the CoNi-e-PNC catalyst shows optimal OER performance with an overpotential of 0.24 V at 10 mA cm^-2 in alkaline media, outperforming those of the ever-reported CoNi-based catalysts. Besides, CoNi-e-PNC catalyst also demonstrates high OER stability with slight current decrease after 100 h.

Designed Formation of Hybrid Nanobox Composed of Carbon Sheathed CoSe2 Anchored on Nitrogen-Doped Carbon Skeleton as Ultrastable Anode for Sodium-Ion Batteries

Research on sodium-ion batteries (SIBs) has recently been revitalized due to the unique features of much lower costs and comparable energy/power density to lithium-ion batteries (LIBs), which holds great potential for grid-level energy storage systems. Transition metal dichalcogenides (TMDCs) are considered as promising anode candidates for SIBs with high theoretical capacity, while their intrinsic low electrical conductivity and large volume expansion upon Na⁺ intercalation raise the challenging issues of poor cycle stability and inferior rate performance. Herein, the designed formation of hybrid nanoboxes composed of carbon-protected CoSe₂ nanoparticles anchored on nitrogen-doped carbon hollow skeletons (denoted as CoSe₂ @C∩NC) via a template-assisted refluxing process followed by conventional selenization treatment is reported, which exhibits tremendously enhanced electrochemical performance when applied as the anode for SIBs. Specifically, it can deliver a high reversible specific capacity of 324 mAh g^-1 at current density of 0.1 A g^-1 after 200 cycles and exhibit outstanding high rate cycling stability at the rate of 5 A g^-1 over 2000 cycles. This work provides a rational strategy for the design of advanced hybrid nanostructures as anode candidates for SIBs, which could push forward the development of high energy and low cost energy storage devices.

Effect of Preparation Method of Co-Ce Catalysts on CH4 Combustion

Transition metal oxides have recently attracted considerable attention as candidate catalysts for the complete oxidation of methane, the main component of the natural gas, used in various industrial processes or as a fuel in turbines and vehicles. A series of novel Co-Ce mixed oxide catalysts were synthesized as an effort to enhance synergistic effects that could improve their redox behavior, oxygen storage ability and, thus, their activity in methane oxidation. The effect of synthesis method (hydrothermal or precipitation) and Co loading (0, 2, 5, and 15 wt.%) on the catalytic efficiency and stability of the derived materials was investigated. Use of hydrothermal synthesis results in the most efficient Co/CeO2 catalysts, a fact related with their improved physicochemical properties, as compared with the materials prepared via precipitation. In particular, a CeO2 support of smaller crystallite size and larger surface area seems to enhance the reducibility of the Co3O4/CeO2 materials, as evidenced by the blue shift of the corresponding reduction peaks (H2-TPR, H2-Temperature Programmed Reduction). The limited methane oxidation activity over pure CeO2 samples is significantly enhanced by Co incorporation and further improved by higher Co loadings. The optimum performance was observed over a 15 wt% Co/CeO2 catalyst, which also presented sufficient tolerance to water presence.

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.

Strong metal–support interactions of Co-based catalysts facilitated by dopamine for highly efficient ammonia synthesis: in situ XPS and XAFS spectroscopy coupled with TPD studies

We report a new strategy for strengthening metal–support interaction and stabilizing Co nanoparticles at high temperature.

The synergistic effects between Ce and Cu in CuyCe1−yW5Ox catalysts for enhanced NH3-SCR of NOx and SO2 tolerance

Non-manganese-based metal oxides are promising catalysts for the NH₃-SCR (selective catalytic reduction) of NO_x at low temperatures.

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).

Synthesis of catalytically active bimetallic nanoparticles within solution-processable metal–organic-framework scaffolds

Bimetallic alloy nanoparticles are synthesized by in situ reduction of mixed metal ions inside CD-MOFs.