Selective Oxidation Of Ethanol Research Articles

Synthesis of Mo–Cr Mixed Metal Oxide Catalyst Based on Pentagonal Unit Assembly and Selective Oxidation of Ethanol

Synthesis of Mo–Cr Mixed Metal Oxide Catalyst Based on Pentagonal Unit Assembly and Selective Oxidation of Ethanol

(Invited) Coupling Metal-Organic Framework with Oxide Photocatalyst for Selective Photoredox Reactions

Oxide photocatalyst is one of the major groups of photoactive semiconductors capable of facilitating useful photoredox reactions for a variety of energy and environmental-related applications. The intrinsic optical and electronic properties of oxide photocatalysts encounter a number of limitations. Often, the wide band gap and inferior photoexcited charge transportation within oxide semiconductors are highlighted. Wide band gap limits the light absorption while inadequate charge transport properties such as low charge mobility and short lifetime can only afford mild photoactivities. Strategies have been formulated to improve the performance of these semiconductors in order to bridge the gap for practical use. Among many existing strategies, coupling oxide photocatalysts with metal-organic framework (MOF) has gained attention in the community as one potential method to improve performance (e.g. higher light absorption, better product yield, prolonged stability and etc). Attaching photoactive MOFs onto or “doping” metallic element into oxide photocatalyst may extend the light absorption of the composite materials. Improved product yield is, more often, attributed to the adsorption capacity of MOFs towards reactant, which bring about the localised concentration of reactants adjacent to active sites of photocatalyst. Encapsulation of oxide photocatalyst by MOFs can suppress the undesirable side reactions (such as preventing Cu2O from direct contact with moisture) to prolong the stability of oxide photocatalyst.In this presentation, in addition to the above mentioned advantages of MOFs, the role of MOFs in tuning the selectivity of product formation will also be examined and discussed. Figure 1 shows an example of improved selective oxidation of ethanol to form acetaldehyde using ZIF-8 encapsulated ZnO. Selectivity towards acetaldehyde has been improved from ~79% to ~92% with stable photocatalytic activity.1 In another work, Cu2O covered by Cu-MOF has afforded selective CO2 photoreduction to CH4.2 We believe there is charge interaction between the oxide photocatalyst and the adjacent MOF structure. Transfer of photoexcited electrons from the conduction band of Cu2O to the LUMO level of non-excited wide band gap Cu-MOF has been indicated using time-resolved photoluminescence. Because photocatalytic reactions are the results of electron transfer between photocatalyst and reactants, the presence of photocharge interplay between oxide photocatalyst and MOFs may provide new room for exploration as it has demonstrated significant influence in the selectivity of product formation. Figure 1. Example of improved product selectivity by incorporating MOFs to oxide photocatalyst. The left figure indicates the improved formation of acetaldehyde from photocatalytic ethanol oxidation. The right figure shows the reasonable stability of the MOF-oxide photocatalyst under illumination. Reference: H. Wu, T. H. Tan, R. Liu, H. -Y. Hsu, Y. H. Ng, Selective Ethanol Oxidation to Acetaldehyde on Nanostructured Zeolitic Imidazolate Framework-8-wrapped ZnO Photothermocatalyst Thin Films, Solar RRL 2021, 5, 2000423.H. Wu, X. Y. Kong, X. Wen, S. –P. Chai, E. C. Lovell, J. Tang, Y. H. Ng, Metal-Organic Framework Decorated Cuprous Oxide Nanowires for Long-lived Charges Applied in Selective Photocatalytic CO2 Reduction to CH4. Angew. Chem. Int. Ed. 2021, 60, 8455-8459. Figure 1

A re-useable microreactor for dynamic and sensitive photocatalytic measurements: Exemplified by the photoconversion of ethanol on Pt-loaded titania P25.

Despite numerous advancements in synthesizing photoactive materials, the evaluation of their catalytic performance remains challenging since their fabrication often involves tedious strategies, yielding only low quantities in the μ-gram scale. In addition, these model catalysts exhibit different forms, such as powders or film(-like) structures grown on various supporting materials. Herein, we present a versatile gas phase μ-photoreactor, compatible with different catalyst morphologies, which is, in contrast to existing systems, re-openable and -useable, allowing not only post-characterization of the photocatalytic material but also enabling catalyst screening studies in short experimental time intervals. Sensitive and time-resolved reaction monitoring at ambient pressure is realized by a lid-integrated capillary, transmitting the entire gas flow from the reactor chamber to a quadrupole mass spectrometer. Due to the microfabrication of the lid from borosilicate as base material, 88% of the geometrical area can be illuminated by a light source, further enhancing sensitivity. Gas dependent flow rates through the capillary were experimentally determined to be 1015-1016 molecules s-1, and in combination with a reactor volume of 10.5 μl, this results in residence times below 40s. Furthermore, the reactor volume can easily be altered by adjusting the height of the polymeric sealing material. The successful operation of the reactor is demonstrated by selective ethanol oxidation over Pt-loaded TiO2 (P25), which serves to exemplify product analysis from dark-illumination difference spectra.

Energy-efficient hydrogen production coupled with simultaneous electrosynthesis of acetate over a mesoporous OsRh film

A mesoporous OsRh film is grown on Ni foam for energy-saving hydrogen production and selective oxidation of ethanol to acetate with high efficiency.

Tuning the Selective Ethanol Oxidation on Tensile-Trained Pt(110) Surface by Ir Single Atoms.

Development of efficient and robust electrocatalysts for complete oxidation of ethanol is critical for the commercialization of direct ethanol fuel cells. However, the complete oxidation of ethanol suffers from poor efficiency due to the low C1 pathway selectivity. Herein, single-atomic Ir (Ir1 ) on hcp-PtPb/fcc-Pt core-shell hexagonal nanoplates (PtPb@PtIr1 HNPs) enclosed by Pt(110) surface with a 7.2% tensile strain is constructed to drive complete electro-oxidation of ethanol. Benefiting from the construction of Ir1 sites, the PtPb@PtIr1 HNPs exhibit a Faraday efficiency of 57.93% for the C1 pathway, which is ≈8.3 times higher than that of the commercial Pt/C-JM. Furthermore, the PtPb@PtIr1 HNPs show a top-ranked electro-activity achieving 45.1-fold and 56.3-fold higher than the specific and mass activities of Pt/C-JM, respectively. Meanwhile, the durability can be significantly enhanced by the construction of Ir1 sites. Density functional theory calculations indicate that the strong synergy on the PtPb@PtIr1 HNPs surface significantly promotes the breaking of CC bond of CH2 CO* and facilitates CO oxidation and suppresses the deactivation of the catalyst. This work offers a unique single-atom approach using low-coordination active sites on shape-controlled nanocrystals to tune the selectivity and activity toward complicated catalytic reactions.

Selective oxidation of ethanol into acetaldehyde catalyzed by novel Mg-Mo/MCM-41 mesoporous molecular meshes

Molecular sieves of MCM-41 impregnated with MgO, MoO3, and Mo2C synthesized using a wet impregnation method. The compounds developed herein, were characterized by means of XRD, SEM-EDS and FT-IR techniques. The production capacity of acetaldehyde from ethanol was analyzed by catalytic processes employing as-synthesized MCM-41. The obtained results show that the changes in crystallinity of MCM-41 were due to the impregnation of oxides, which generate damage to the structure of MCM-41. However, the characteristics of the compounds are favorable, allowing them to be used as heterogeneous catalyst material due to the similarity of the characteristics between MCM-41 with and without of Mg and Mo oxides. The catalysis tests show the influence between the type of catalyst used and the temperature applied to the production process of acetaldehyde from ethanol, obtaining the best results in the samples impregnated with Mo2C at 250 °C, with a production percentage of acetaldehyde of 80.7% and 77.9% for the catalysts impregnated with 0.5% and 2.0% Mg and 3.0% Mo carbide, respectively.

Selective oxidation of ethanol to ethylene oxide with a dual-layer concept

Ethylene oxide is mainly produced from fossil-based ethylene. Only minor amounts of EO are based on renewable ethanol in a three-step process consisting of an ethanol dehydration step, an ethylene purification step, and an epoxidation step. We herein present a new one-step process for the selective oxidation of ethanol to ethylene oxide by a novel dual-layer concept without intermediate ethylene purification. Ethanol is dehydrated in one reactor on a first catalyst bed to ethylene which is subsequently epoxidized over a silver catalyst. The dual-layer arrangement allowed stable operation over more than 60 h and state-of-the-art conversions and selectivities were obtained.

Nickel chalcogenides as selective ethanol oxidation electro-catalysts and their structure-performance relationships.

Five nickel chalcogenides have been studied and they showed high selectivity towards selective ethanol electro-oxidation to acetic acid. The activities of the different nickel chalcogenides are correlated with the Ni-Ni projected distances of the catalysts.

Graphitic Carbon Nitride as a Sustainable Catalyst for Selective Ethanol Oxidation

Graphitic carbon nitride (g-C3N4) is obtained via a simple procedure consisting of melamine heating in air without any templates and additional treatments. The prepared g-C3N4, being a metal-free m...

Selective Ethanol Oxidation Reaction at the Rh-SnO2 Interface.

Direct ethanol fuel cells (DEFCs) are regarded as an attractive power source with high energy density, bio-renewability, and convenient storage and transportation. However, the anodic reaction of DEFCs, that is, the ethanol oxidation reaction (EOR), suffers from poor efficiency due to the low selectivity to CO2 (C1 pathway) and high selectivity to CH3 COOH (C2 pathway). In this study, the selective EOR to CO2 can be achieved at the Rh-SnO2 interface in SnO2 -Rh nanosheets (NSs). The optimized catalyst of 0.2SnO2 -Rh NSs/C exhibits excellent alkaline EOR performance with a mass activity of 213.2 mA mgRh -1 and a Faraday efficiency of 72.8% for the C1 pathway, which are 1.7 and 1.9 times higher than those of Rh NSs/C. Mechanism studies indicate that the strong synergy at the Rh-SnO2 interface significantly promotes the breaking of CC bond of C2 H5 OH to form CO2 , and facilitates oxidation of the poisonous intermediates (* CO and * CH3 ) to suppress the deactivation of the catalyst. This work not only provides a highly selective, active, and stable catalyst for the EOR, but also promotes fundamental research for the design of efficient catalysts via interface modification.

Heteronanostructured Photocatalysts with Epitaxial Junctions between the Components

Heteronanostructured (HNS) photocatalysts are the key material for various important solar-to-chemical transformations. In the semiconductor photoelectrodes, efficient charge separation can be achieved by the Schottky barrier. However, in the particulate HNS photocatalysts, the dimension of semiconductor is usually too small to accommodate the space charge layer. Even if the space charge layer can be formed at the initial stage, the band bending would become weak at the photostationary state due to the accumulation of the electrons in the conduction band. Thus, the major subject in the HNS photocatalysts is the enhancement of charge separation through the efficient interfacial charge transfer between the components for which the construction of the high-quality interface is crucial [1]. On the other hand, Au NP possesses strong and broad absorption in the visible region due to the localized surface plasmon resonance, and loading Au NPs on wide gap semiconductor photocatalysts such as TiO2, SnO2, and ZnO (Au/semiconductor) can induce the visible-light responsiveness and/or work as a catalyst for various reactions [1]. Importantly, the optical property and catalytic activity of Au NPs strongly depend on the size and shape.This talk focusses on our recent works on the interfacial control in the HNSs at an atomic level, and the effects on the photocatalytic activity. Firstly, a novel nanoscale charge separation mechanism is presented in a HNS consisting of SnO2 nanorods and rutile TiO2 with a heteroepitaxial (HEPI) junction (SnO2-NR#TiO2, # denotes HEPI junction). SnO2-NR#TiO2 shows photocatalytic activity for selective oxidation of ethanol to acetaldehyde much higher than the physical mixture of SnO2 and TiO2 [2]. Secondly, the SnO2-NR#TiO2 charge separator was further modified with Au NPs (Au/SnO2-NR#TiO2) to impart visible-light activity. The Au/SnO2-NR#TiO2 plasmonic photocatalyst exhibits a high level of visible-light activity for the synthesis of H2O2 by two-electron oxygen reduction reaction (ORR) with the assistance of the catalytic activity of Au NP [3]. Thirdly, the HEPI junction-induced shape change of Au NPs is shown to occur on the surface of ZnO in the Au#ZnO system. The extremely high UV-light activity of Au#ZnO for two-electron ORR far exceeding that of Au/TiO2 is discussed in terms of the catalytic activity of Au NPs and the adsorption ability of ZnO for H2O2 [4].[1] H. Tada, Dalton Trans. 2019, 48, 6308, and the references therein.[2] K. Awa, R. Akashi, A. Akita, S. Naya, H. Kobayashi, H. Tada, ChemPhysChem 2019, 20, 2155.[3] K. Awa, S. Naya, M. Fujishima, H. Tada, J. Phys. Chem. C 2020, 124, 7599.[4] M. Teranishi, S. Naya, H. Tada, J. Am. Chem. Soc. 2010, 132, 7850.

Selective Ethanol Oxidation to Acetaldehyde on Nanostructured Zeolitic Imidazolate Framework‐8‐Wrapped ZnO Photothermocatalyst Thin Films

Photothermocatalytic ethanol oxidation to acetaldehyde offers an alternative technology in synthesizing high‐value‐added chemicals. However, the practical application is hindered by the competition from overoxidation leading to complete mineralization. Herein, the 1D nanostructured ZnO@zeolitic imidazolate framework‐8 (ZIF‐8) composite is reported as an efficient photothermocatalyst, which shows improved conversion efficiency and high catalytic selectivity and durability compared with the parent ZnO nanorods, for continuous ethanol oxidation in a flow system. The ZnO@ZIF‐8 composite achieves a high selectivity of 91.5% toward acetaldehyde production. The underlying mechanism is probed using electrochemical impedance spectroscopy, N2 adsorption–desorption isotherms, transient open‐circuit potential, and steady‐state and time‐resolved photoluminescence spectroscopy. Collectively, the probings show that the improved performance originates from 1) facilitated charge separation; 2) lowered oxidation potential holes; 3) enlarged surface area; and 4) preferred reaction routes. This work provides a new perspective for the design of a hybrid photothermocatalyst for selective solar energy conversion into desirable chemicals.

Highly dispersed gold nanoparticles on metal-doped α-MnO2 catalysts for aerobic selective oxidation of ethanol

Gold nanopaticles (AuNPs) supported on metal-doped α-MnO2 (M-OMS, M = Na, Mg, Al, Fe, Cu, Zn) have been designed for gas-phase selective oxidation of ethanol. Gold loading by colloidal deposition (CD) and deposition precipitation (DP) methods were employed to prepare Au/M-OMS catalysts, and Au/M-OMS-CD showed better gold dispersion and catalytic stability. Au/Cu-OMS-CD achieved the highest acetaldehyde yield (80%) and space-time-yield (3.0 g gcat−1 h−1) at 200 °C, which are higher than previously reported gold catalysts. Such good performance was ascribed to the moderate surface reduction caused by the CD method and the copper-promoted metal-support synergy between AuNPs and Cu-OMS.

Elucidating structure-performance correlations in gas-phase selective ethanol oxidation and CO oxidation over metal-doped γ-MnO2

Despite of considerable efforts on the MnO2-based catalytic combustion, the different structural and component requirements of MnO2 for gas-phase selective oxidation and complete oxidation largely remain unknown. By comparing four types of MnO2 with different crystal structures (α, β, γ and δ), γ-MnO2 was found to be the most efficient catalyst for both aerobic selective oxidation of ethanol and CO oxidation. The structural effect of γ-MnO2 was further investigated by doping metal ions into the framework and by comparing the catalytic performance in the gas-phase aerobic oxidation of CO and ethanol. Among ten M-γ-MnO2 catalysts, Zn-γ-MnO2 showed the lowest temperature (160 °C) for achieving 90% CO conversion. The CO oxidation activity of the M-γ-MnO2 catalysts was found to be more relevant to the surface acidity-basicity than the reducibility. In contrast, surface reducibility has been demonstrated to be more crucial in the gas-phase ethanol oxidation. Cu-γ-MnO2 with higher reducibility and more oxygen vacancies of Mn2+/Mn3+ species exhibited higher catalytic activity in the selective ethanol oxidation. Cu-γ-MnO2 achieved the highest acetaldehyde yield (75%) and space-time-yield (5.4 g gcat–1 h–1) at 200 °C, which are even comparable to the results obtained by the state-of-the-art silver and gold-containing catalysts. Characterization results and kinetic studies further suggest that the CO oxidation follows the lattice oxygen-based Mars-van Krevelen mechanism, whereas both surface lattice oxygen and adsorbed oxygen species involve in the ethanol activation.

Synergistic effect between gold nanoparticles and Fe-doped γ-MnO2toward enhanced aerobic selective oxidation of ethanol

Gold nanoparticles supported on Fe-doped γ-MnO2were found to show a strong synergistic effect in the aerobic selective oxidation of ethanol to acetaldehyde.

Efficient UV-vis-IR photothermocatalytic selective ethanol oxidation on MnOx/TiO2 nanocomposites significantly enhanced by a novel photoactivation

MnOx/TiO2 nanocomposites exhibit good catalytic activity and excellent durability for photothermocatalytic selective ethanol oxidation under UV-vis-IR and IR irradiation. A novel photoactivation is found to significantly enhance catalytic activity due to activation energy being reduced upon irradiation.

Selective oxidation of ethanol on V-MCM-41 catalysts

Catalysts V-MCM-41 with different V contents (0.09-0.90 wt.%), synthesized by the template ion-exchange (TIE) method, have been investigated for acetaldehyde production by selective oxidation of ethanol, studying the effects of reaction temperature, O2/ethanol molar ratio and V content of the catalyst. The catalysts were characterized by X-ray diffraction (XRD), Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), diffuse reflectance UV–vis spectroscopy (UV–vis-DR), N2 adsorption and Fourier transform infrared spectroscopy (FT-IR) with pyridine adsorption. All the catalysts showed good structural regularity and high specific areas. Analysis by UV–vis-DR showed the presence of different V species: isolated V cations incorporated to the siliceous structure or on the pore wall, clusters with different sizes and segregated nano-oxides in different proportions depending on the V content. Under the reaction conditions explored, the maximum acetaldehyde selectivity (90.5%) was reached at 623 K but the maximum yield (48% yield with 77% selectivity) was reached at 673 K, using a feed molar ratio O2/ethanol = 1. The activity of the catalysts decreased with the increase in V contents, due to the different type and increasing aggregation of V species, the most active catalyst being the one with the highest dispersion of isolated tetrahedral V species.

SYNTHESIS OF СеО2–МоО3 CATALYSTS OF SELECTIVE ETHANOL OXIDATION BY NON-TRADITIONAL METHODS

The influence of mechanochemical (MChT) and ultrasonic (UST) treatment on physic-chemical properties of СеО2-МоО3=1:1 composition was studied. The prepared samples were characterized by methods of XRD, ESR, N2 adsorption, SEM and TEM methods. The catalytic properties of obtained samples were studied in selective ethanol oxidation reaction. It was established the increase of specific surface area, decrease crystallites size and nanostructures formation of type “core-shell” due to MCh and US treatment. The change of physico-chemical properties of the compositions as a result of their mechano- and sonochemical treatment leads to increase their catalytic properties. The samples obtained after MCh and US treatments demonstrate very promising results in oxidative dehydrogenation of ethanol to acetaldehyde and the treated compositions permit to obtain the acetaldehyde selectivity equal 97 % at reaction temperature about 200ºC. It was shown that mechno- and sonochemical treatments of oxide mixture allow to obtain a high acetic aldehyde yield (97%) at 215°C and productivity on this product 1.8 mol/kg·h.

Front Cover: Highly Efficient and Selective Oxidation of Ethanol to Acetaldehyde by a Hybrid Photocatalyst Consisting of SnO2 Nanorod and Rutile TiO2 with Heteroepitaxial Junction (ChemPhysChem 17/2019)

Front Cover: Highly Efficient and Selective Oxidation of Ethanol to Acetaldehyde by a Hybrid Photocatalyst Consisting of SnO₂ Nanorod and Rutile TiO₂ with Heteroepitaxial Junction (ChemPhysChem 17/2019)

Highly Efficient and Selective Oxidation of Ethanol to Acetaldehyde by a Hybrid Photocatalyst Consisting of SnO2 Nanorod and Rutile TiO2 with Heteroepitaxial Junction

AbstractThe front cover artwork is provided by the group of Prof. Hiroaki Tada (Kindai University, Japan). The image shows the heteroepitaxial junction‐induced band bending can enhance the charge separation in nanohybrid photocatalysts. Read the full text of the Communication at 10.1002/cphc.201900632.