Experimental and Theoretical Investigation of Interfacial Engineering in Fe2O3/NiFe2O4 Heterostructures toward the Cycloaddition of CO2 with Styrene Oxide.

The chemical fixation of CO2 into epoxides for the synthesis of cyclic carbonates is an appealing solution to both reduce global CO2 emission and produce fine chemicals, but it is still a prime challenge to develop a low-cost, earth-abundant, yet efficient solid catalyst. Herein, Fe2O3/NiFe2O4 heterostructures are facilely constructed for the highly efficient cycloaddition of CO2 with styrene oxide (SO) to produce styrene carbonate (SC). Both experimental findings and density functional theory (DFT) calculations substantiate the prominent electron transfer and charge redistribution within the heterointerfaces between the biphasic components, which induce a unique interfacial microenvironment that can facilitate the adsorption and activation of SO. This endows the biphasic catalyst with a substantially higher reactivity than the individual components. This study sheds new insights into the establishment of heterostructured catalysts consisting of transitional metal oxides for the high-efficiency production of SC from the cycloaddition of CO2 with SO.

Manipulation of Electronic Effect and Assembly Architecture to Invoke Oxidation of Ethylbenzene by Hierarchical Co3O4 Wreaths.

A high-performance transition-metal oxide catalyst can be designed by appropriately integrating the concepts of morphology regulation and electronic structure modulation. In this work, hierarchical Co3O4 wreaths (CCW) enriched with oxygen vacancies (Ov) were facilely constructed for the selective oxidation of ethylbenzene (EB) to acetophenone (AP). Under the screened optimal reaction conditions, the CCW catalyst can offer a 79.1% conversion of EB (ri = 0.244 mol gcat-1 h-1) accompanied by a selectivity of 92.3% to AP. The good reaction performance can be attributed to the cooperation of defect engineering and architecture design, which can synergistically facilitate the EB oxidation performance by augmenting the intrinsic reactivity and accessibility of active sites. This work presents a reliable route to construct a high-performance transitional metal oxide catalyst via manipulation of electronic effect and assembly architecture for the selective oxidation of EB and beyond.

Hexavalent Chromium Reduction Mediated by Interfacial Electron Transfer over the Co@NC Nanosheet-Assembled Microflowers.

The reductive transformation of Cr(VI) into Cr(III) mediated by formic acid with efficient, stable, and cost-effective catalysts is a promising strategy for remediating Cr(VI) contamination. Herein, we report the facile construction of uniform Co@NC nanosheet-assembled microflowers for the reduction of Cr(VI). Both experimental results and density functional theory (DFT) calculations reveal the vital role of the intensive interfacial electronic interaction between Co nanoparticles and the N-doped carbon layer in facilitating the anchoring and dispersion of Co nanoparticles within the carbon framework. The interfacial electron transfer from Co to NC contributes to the interaction with Cr2O72- ions, promoting the subsequent H-transfer reaction. A Langmuir-Hinshelwood kinetic model has been established for the Cr(VI) reduction catalyzed by the CNCF2 (pyrolyzed at 700 °C), which shows a superior reaction performance. This study provides a facile strategy to delicately design well-assembled heterostructures with rich interfaces and strong interfacial interactions for a series of applications in environmental/thermal catalysis.

Coupled Interface and Oxygen-Defect Engineering in Co3O4/CoMoO4 Heterostructures toward Active Oxidation of Ethylbenzene.

The catalytic oxidation of ethylbenzene (EB) is a promising route to produce acetophenone (AcPO). Unfortunately, it remains a great challenge to achieve the highly efficient oxidation of EB under solvent-free conditions using molecular oxygen as the sole oxidant. In this contribution, we present a facile strategy to construct hierarchical oxygen vacancy-rich Co3O4/CoMoO4 heterostructures (Vö-CCMO), which delivers a high yield value of 74.5% at 83.2% conversion of EB and selectivity of 89.6% to AcPO. Both experimental studies and theoretical calculations substantiate the important role of oxygen-defect engineering triggered by the modified chemistry environment at the interfaces between the biphasic phases, which contributes to the good catalytic performance. This work illustrates a promising paradigm for the exploit of advanced catalysts toward boosting EB oxidation reaction in a more practical way.

Beneficial Synergistic Intermetallic Effect in ZnCo2O4 for Enhancing the Limonene Oxidation Catalysis.

Utilization of naturally occurring limonene from renewable biomass as a key starting material for the synthesis of valuable chemicals is a promising avenue to reduce both the dependence on nonrenewable fossil fuels and global CO2 emission. Herein, we report a highly active tremella-like ZnCo2O4 catalyst for the selective oxidation of limonene with molecular oxygen under mild reaction conditions. The developed ZnCo2O4 catalyst exhibits an appealing reaction performance with a limonene conversion of 93.5% (reaction rate of 0.0823 mmol gcat-1 h-1) and selectivity of 75.8% for 1,2-limonene oxide (LO), far outperforming the monometallic oxides of ZnO and Co3O4. Detained experimental characterizations and analyses manifest that the substitution of Zn into the Co3O4 framework can facilitate the formation of more unsaturated coordination sites and oxygen vacancies due to the modified chemical environment of Co atoms, inducing a beneficial synergistic intermetallic effect for the limonene oxidation catalysis.

Constructing a Pd-Co Interface to Tailor a d-Band Center for Highly Efficient Hydroconversion of Furfural over Cobalt Oxide-Supported Pd Catalysts.

Cobalt is an alternative catalyst for furfural hydrogenation but suffers from the strong binding of H and furan ring on the surface, resulting in low catalytic activity and chemoselectivity. Herein, by constructing a Pd-Co interface in cobalt oxide-supported Pd catalysts to tailor the d-band center of Co, the concerted effort of Pd and Co boosts the catalytic performance for the hydroconversion of furfural to cyclopentanone and cyclopentanol. The increased dispersion of Pd on acid etching Co3O4 promotes the reduction of Co3+ to Co0 by enhancing hydrogen spillover, favoring the creation of the Pd-Co interface. Both experimental and theoretical calculations demonstrate that the electron transfer from Pd to Co at the interface results in the downshift of the d-band center of Co atoms, accompanied by the destabilization of H and furan ring adsorption on the Co surface, respectively. The former improves the furfural hydrogenation with TOF on Co elevating from 0.20 to 0.62 s-1, and the latter facilitates the desorption of formed furfuryl alcohol from the Co surface for subsequently hydrogenative rearrangement of the furan ring to cyclopentanone on acid sites. The resultant Pd/Co3O4-6 catalyst delivers superior activity with a 99% furfural conversion and 85% overall selectivity toward cyclopentanone/cyclopentanol. We anticipate that such a concept of tailoring the d-band center of Co via interface engineering provides novel insight and feasible approach for the design of highly efficient catalysts for furfural hydroconversion and beyond.

Heterostructured V2O5/FeVO4 for enhanced liquid-phase epoxidation of cyclooctene.

Efficient cyclooctene epoxidation process under mild reaction conditions highly relies on the rational design and synthesis of high-performance heterogeneous catalysts. Herein, we report the facile one-pot synthesis of V2O5/FeVO4 heterostructures featured with heterointerfaces for the boosted epoxidation of cyclooctene. The intensive interfacial electronic interaction between the V2O5 and FeVO4 phases is versatile in the modulation of coordination microenvironment and formation of abundant oxygen vacancies, contributing to the performance enhancement. Under the optimal reaction conditions, a high yield of 87.0% can be achieved with the cyclooctene conversion of 96.5% (initial reaction rate of 55.1 mmol gcat-1 h-1) and cyclooctene oxide selectivity of 90.2%. Additionally, the V2O5/FeVO4 catalyst is stable and recyclable, endowing it a promising prospect for practical applications. This study demonstrates that the application of interface engineering strategy can be an appealing avenue towards the development of high-performance catalysts for epoxidation of cyclooctene and beyond.

Promoted selective oxidation of ethylbenzene in liquid phase achieved by hollow CeVO4 microspheres.

Herein, we developed a series of CeVO4 samples with hierarchical hollow microsphere-like structure obtained at different calcination temperatures for the selective oxidation of ethylbenzene (EB) to acetophenone (AcPO) in the presence of TBHP. The optimized catalyst (CVO-500) exhibits a very high yield value of 95.0% (initial reaction rate of 49.4 mmol gcat-1 h-1) under the optimal reaction conditions. Importantly, the representative CVO-500 catalyst presents high stability, with the reaction performance well maintained after five consecutive uses. It has been indicated that the redox V5+/V3+ sites serve as the main active centers, while the electronic interaction and redox transformation between Ce and V facilitates the hopping of V5+/V3+ and the generation of oxygen vacancies. The bimetallic synergy between V and Ce thus endows the CVO-500 catalyst an excellent performance in the EB oxidation reaction. This work paves the way for the exploit of high-performance and cost-effective catalyst for the EB oxidation and beyond.

Pumpkin-derived N-doped porous carbon for enhanced liquid-phase reduction of 2-methyl-4-nitrophenol.

Metal-free catalysts with environmental friendless, cost-competitiveness and less susceptibility to leaching and poisoning over metal-based catalysts, have revolutionized in the catalysis domain. In this respect, we herein report the first application of cheap and abundant pumpkin-derived N-doped porous carbon for the reduction of 2-methyl-4-nitrophenol assisted by NaBH4. The obtained catalyst is cost-competitive, efficient and robust, with an attractive mass-normalized rate constant of 4.73 s-1 g-1 and good recycling performance. Systematical analyses demonstrate that the 2-methyl-4-nitrophenol reduction reaction catalyzed by the N-doped carbon proceeds through the Langmuir-Hinshelwood kinetics and the performance enhancement benefits from the strong adsorption and activation of the substrates induced by the electronic modulation in the carbon framework via N-doping. This study opens up new avenues for the high-value use of pumpkin as well as the development of metal-free strategy in more catalytic applications.

Intriguing hierarchical Co@NC microflowers in situ assembled by nanoneedles: Towards enhanced reduction of nitroaromatic compounds via interfacial synergistic catalysis.

Developing highly efficient and cost-effective catalyst with tuned microstructure holds great promise in the reduction of nitroaromatic compounds under mild reaction conditions. Herein, we report a new Co@NC-MF catalyst with a fascinating hierarchical flower-like architecture in situ assembled from uniform Co@NC nanoneedles, which can function as a favorable platform for the efficient reduction of nitroaromatic compounds in the presence of NaBH4. In addition with the structural advantage, the characterization and experimental results demonstrate the enormous advantage of interfacial synergistic catalysis in enhancing the catalytic performance. The outside electron-rich N-doped carbon layer as Lewis basic sites and the inside Co nanoparticles are responsible for the adsorption of 4-nitrophenol (4-NP) and generation of active hydrogen species, respectively. This work contributes to the construction of well-integrated composites with well-balanced interface synergy to boost the catalytic performance in various heterogeneous reactions.

Promotional effect of Mn-doping on the catalytic performance of NiO sheets for the selective oxidation of styrene.

The direct oxidation of styrene into high-value chemicals under mild reaction conditions remains a great challenge in both academia and industry. Herein, we report a successful electronic structure modulation of intrinsic NiO sheets via Mn-doping towards the oxidation of styrene. By doping NiO with only a small content of Mn (Mn/Ni atomic ratio of 0.030), a 75.0% yield of STO can be achieved under the optimized reaction conditions, which is 2.13 times higher than that of the pure NiO. In addition, the catalyst exhibits robust stability and good recycling performance. The performance enhancement originates from the synergistic effect regarding the abundant Ni(II) species, the rich oxygen vacancy sites and the large amount of surface redox centers. This work provides new findings of the elemental-doping-induced multifunctionality in designing powerful catalysts for the efficient and selective oxidation of styrene and beyond.

Boosting styrene epoxidation via CoMn2O4 microspheres with unique porous yolk-shell architecture and synergistic intermetallic interaction.

Achieving satisfactory organic transformation reactions under mild conditions using high-performance catalysts that are composed of cost-effective and earth-abundant elements has always been an aspiration for scientists in the field of catalysis. In this work, CoMn2O4 microspheres with intriguing porous yolk-shell architecture have been constructed by a facile solvothermal reaction and post-calcination treatment, and were employed for the first time in the epoxidation reaction of styrene (SER). Among the series of CoMn2O4 catalysts, the one calcined at 600 °C (CMO-600) displays superior catalytic performance in the SER, achieving an excellent conversion of 97.7%, a prominent selectivity of 83.7% to SO and a good recycling performance. The remarkable SER performance of the CMO-600 benefits from the collaborative influences derived from the unique porous yolk-shell architecture and the synergy of the two metal centers regarding high surface Mn2+/ Mn3+ atomic ratio, abundant redox couples and rich oxygen vacancies. The reaction pathway analysis and the activation energy measurement were performed as well to unravel the inner relationship between the catalytic behavior and the catalyst properties. This study affords a fresh impetus to the developing of high-performance bimetallic oxides for oxidation reactions in organic catalysis.

Hierarchical hollow nickel silicate microflowers for selective oxidation of styrene.

Developing heterogeneous non-precious metal catalysts that can achieve high catalytic activity and good product selectivity at the same time is still a challenging and interesting work for the selective oxidation of styrene into valuable chemicals from environmental and industrial points of view. Herein, hierarchical hollow nickel silicate (Ni3Si2O5(OH)4) microflowers assembled from well-defined Ni3Si2O5(OH)4 nanosheets have been prepared by a facile one-pot hydrothermal method. The intriguing structure endows the hollow Ni3Si2O5(OH)4 microflowers a high surface area of 177.4 m2 g-1 and an average pore size of 3.9 nm. When employed as a catalyst for the selective oxidation of styrene in the presence of hydrogen peroxide as a ecological sustainable green oxidant, the Ni3Si2O5(OH)4 exhibits an attractive catalytic performance with a remarkably high styrene conversion of 99.3% and a high selectivity of 81.1% to benzaldehyde.

Silver nanoparticles-decorated-Co3O4 porous sheets as efficient catalysts for the liquid-phase hydrogenation reduction of p-Nitrophenol.

Developing proper supports for the anchoring of active metals for various applications has been the focus of high interest over the past decades. Herein, we report the facile construction of Ag nanoparticles (NPs) homogeneously decorated on the Co3O4 porous sheets, which can be employed as an efficient and robust catalyst for the liquid-phase hydrogenation reduction of p-Nitrophenol (PNP). The excellent catalytic performance can be attributed to the synergistic effect of the evenly distributed Ag NPs, the porous structure with high surface area, and the electronic synergy between the Ag NPs and the Co3O4 support. These merits, providing abundant and stable active sites, electron-enhanced area in the interface and fast interfacial electron transfer to the PNP molecules, work in tandem to achieve the good reaction results. In addition, the apparent activation energy was measured, and a Langmuir-Hinshelwood model was suggested for the mechanism of the PNP reduction process.

Density functional theory study of selective aerobic oxidation of cyclohexane: the roles of acetic acid and cobalt ion.

A computational study of cyclohexane autoxidation and catalytic oxidation to a cyclohexyl hydroperoxide intermediate (CyOOH), cyclohexanol, and cyclohexanone has been conducted using a hybrid density functional theory method. The activation of cyclohexane and O2 is the rate-determining step in the formation of CyOOH due to its relatively high energy barrier of 41.2 kcal/mol, and the subsequent reaction behavior of CyOOH controls whether the production of cyclohexanol or cyclohexanone is favored. Using CH3COOH or (CH3COO)2Co as a catalyst reduces the energy barriers required to activate cyclohexane and O2 by 4.1 or 7.9 kcal/mol, respectively. Employing CH3COOH improves the CyOOH intramolecular dehydration process, which favors the formation of cyclohexanone. The energy barrier to the decomposition of CyOOH to CyO·, an important precursor of cyclohexanol, decreases from 35.5 kcal/mol for autoxidation to 25.9 kcal/mol for (CH3COO)2Co catalysis. (CH3COO)2Co promotes the autoxidation process via a radical chain mechanism. The computational results agree with experimental observations quite well, revealing the underlying role of CH3COOH and Co ion in cyclohexane oxidation. Graphical abstract Through DFT analysis of cyclohexane autoxidation and catalytic oxidation, we reveal the mechanism of the effects of CH3COOH and Co2+ on the reaction routes.

Hollow urchin-like NiO/NiCo2O4 heterostructures as highly efficient catalysts for selective oxidation of styrene.

Three-dimensional (3D) hierarchical hollow urchin-like NiO/NiCo2O4 heterostructures have been prepared via a facile one-pot hydrothermal method. The 3D urchin-like structure brings about high specific surface area of 40.2 m2 g-1. The NiO/NiCo2O4 heterostructures are composed of 59 wt% of NiO and 41 wt% of NiCo2O4 and enriched with NiO-NiCo2O4 phase boundaries. When used as catalysts for styrene oxidation reaction (SOR), the NiO/NiCo2O4 heterostructures present a markedly high selectivity of 90.8% to styrene oxide (SO) and a high SO yield of 81.4%. The high catalytic performance of the NiO/NiCo2O4 heterostructures can be attributed to the high specific surface area and the abundant NiO-NiCo2O4 phase boundaries, both of which contribute to the numerous active sites.

Highly selective oxidation of styrene to benzaldehyde over a tailor-made cobalt oxide encapsulated zeolite catalyst.

A tailor-made catalyst with cobalt oxide particles encapsulated into ZSM-5 zeolites (Co3O4@HZSM-5) was prepared via a hydrothermal method with the conventional impregnated Co3O4/SiO2 catalyst as the precursor and Si source. Various characterization results show that the Co3O4@HZSM-5 catalyst has well-organized structure with Co3O4 particles compatibly encapsulated in the zeolite crystals. The Co3O4@HZSM-5 catalyst was employed as an efficient catalyst for the selective oxidation of styrene to benzaldehyde with hydrogen peroxide as a green and economic oxidant. The effect of various reaction conditions including reaction time, reaction temperature, different kinds of solvents, styrene/H2O2 molar ratio and catalyst dosage on the catalytic performance were systematically investigated. Under the optimized reaction condition, the yield of benzaldehyde can achieve 78.9% with 96.8% styrene conversion and 81.5% benzaldehyde selectivity. Such an excellent catalytic performance can be attributed to the synergistic effect between the confined reaction environment and the proper acidic property. In addition, the reaction mechanism with Co3O4@HZSM-5 as the catalyst for the selective oxidation of styrene to benzaldehyde was reasonably proposed.

Metallic cobalt nanoparticles imbedded into ordered mesoporous carbon: A non-precious metal catalyst with excellent hydrogenation performance.

Ordered mesoporous carbon (OMC)-metal composites have attracted great attention owing to their combination of high surface area, controlled pore size distribution and physicochemical properties of metals. Herein, we report the cobalt nanoparticles/ordered mesoporous carbon (CoNPs@OMC) composite prepared by a one-step carbonization/reduction process assisted by a hydrothermal pre-reaction. The CoNPs@OMC composite presents a high specific surface area of 544m2g-1, and the CoNPs are uniformly imbedded or confined in the ordered mesoporous carbon matrix. When used as a non-precious metal-containing catalyst for hydrogenation reduction of p-nitrophenol and nitrobenzene, it demonstrates high efficiency and good cycling stability. Furthermore, the CoNPs@OMC composite can be directly used to catalyze the Fischer-Tropsch synthesis for the high-pressure CO hydrogenation, and presents a good catalytic selectivity for C5+ hydrocarbons. The excellent catalytic performance of the CoNPs@OMC composite can be ascribed to synergistic effect between the high specific surface area, mesoporous structure and well-imbedded CoNPs in the carbon matrix.

Three-dimensional nitrogen-doped graphene foam as metal-free catalyst for the hydrogenation reduction of p-nitrophenol.

Developing metal-free catalysts for various applications has been the focus of high interest over the past decade, especially aiming to replace the expensive noble metal-based catalysts. Herein, a well-defined three-dimensional nitrogen-doped graphene foam (3D-NGF) is synthesized and employed as a metal-free catalyst for the hydrogenation reduction of p-Nitrophenol to p-Aminophenol. The apparent activation energy is calculated, and the reaction mechanism with 3D-NGF as the catalyst for the hydrogenation reduction of p-Nitrophenol is proposed. Importantly, the 3D-NGF demonstrates high catalytic activity and robust stability. The high activity can be ascribed to the synergistic effect between the nitrogen-doping induced change in electronic property and the 3D foam-like structure.

Catalytic wet peroxide oxidation of aniline in wastewater using copper modified SBA-15 as catalyst.

SBA-15 mesoporous molecular sieves modified with copper (Cu-SBA-15) were prepared by pH-adjusting hydrothermal method and characterized by X-ray diffraction, BET, transmission electron microscopy, UV-Vis and (29)Si MAS NMR. The pH of the synthesis gel has a significant effect on the amount and the dispersion of copper on SBA-15. The Cu-SBA-15(4.5) (where 4.5 denotes the pH value of the synthesis gel) modified with highly dispersed copper was used as catalyst for the oxidation of aniline by H2O2. The Cu-SBA-15(4.5) shows a higher catalytic activity compared to CuO on the surface of SBA-15. The influences of reaction conditions, such as initial pH of the aqueous solutions, temperature, as well as the dosages of H2O2 and catalyst were investigated. Under weakly alkaline aqueous solution conditions, the aniline conversion, the H2O2 decomposition and the total organic carbon (TOC) removal could be increased significantly compared to the acid conditions. The percentage of leaching Cu(2+) could be decreased from 45.0% to 3.66% when the initial pH of solution was increased from 5 to 10. The TOC removal could be enhanced with the increases of temperature, H2O2 and catalyst dosage, but the aniline conversion and H2O2 decomposition change slightly with further increasing dosage of catalyst and H2O2. At 343 K and pH 8.0, 100% aniline conversion and 66.9% TOC removal can be achieved under the conditions of 1.0 g/L catalyst and 0.05 mol/L H2O2 after 180 min. Although copper might be slightly leached from catalyst, the homogeneous Cu(2+) contribution to the whole catalytic activity is unimportant, and the highly dispersed copper on SBA-15 plays a dominant role.