Bar Of O2 Research Articles

Application of particle-scale modelling to the combustion of a char particle in a fluidised bed of CLOU particles

This research concerns the combustion of a biomass char in a fluidised bed of either inert silica particles or particles of a material capable of supporting combustion using chemical looping oxygen uncoupling (CLOU). An analytical solution for combustion using CLOU was developed, accounting for the chemical reactions occurring within a mass-transfer boundary layer of a finite thickness, surrounding a char particle. The reactions considered were: (1) combustion of char with oxygen to CO and CO2, (2) homogenous reaction of CO with O2, and (3) oxygen release from CLOU particles. The thickness of the boundary layer, γ, was evaluated using correlation in the literature and the combustion of the char particle was modelled as a shrinking particle. Results from the model were compared with experiments performed by combusting char from birch-wood and activated carbon in a fluidised bed (i.d. 30 mm) of either particles capable of CLOU (CuO supported on mayenite) or inert silica sand. Both types of experiments were undertaken with a partial pressure of oxygen, pO2, close to the equilibrium pressure of O2 over CuO at 1173 K, i.e. ∼0.016 bar of O2. The results from the analytical model agreed with the experimental observations from both beds.In addition to the analytical solution, fuller, numerical models were developed, in which a char particle and its surroundings were discretised in 1D to solve the mass balance equations and to assess the validity of the assumptions made in the analytical solution. To establish the range of conditions in which the analytical solution is valid, various cases were simulated. For example, char combustion and gasification in a bed of CuO-particles fluidised by CO2-rich gas. Hence, besides the validation of the analytical solution, the results of the numerical solutions provided insight into the importance of char gasification with CO2 on the overall particle conversion in CLOU at the industrial scale.

The metallic palladium-rhodium solution in interaction with oxygen: The Pd-Rh-O phase diagram and thermodynamics

Palladium and rhodium are two platinum group metals (PGMs) widely operated in the industry because of their high electrical and thermal conductivity. They are also widely used for their catalytic activity for automotive emission control. In the nuclear field, both elements are also known as metallic fission products. Due to their sensitivity towards oxygen, the thermodynamic equilibria of the Pd-Rh-O system have been assessed in this paper thanks to the Calphad method.From this thermodynamic assessment, the linear fit of the Gibbs free energy of PdO is ΔfG°TPdO=-115.8+0.102·T (kJ·mol−1) and its calculated heat of formation is –58.994 kJ·mol−1·at−1. The assessed Pd(g) equilibrium pressure under 1 bar of O2 is:log10pPdbar=6.560-19046.9TThe Pd(g) and PdO(g) equilibrium pressures at PdO decomposition are respectively:log10pPdbar=6.7269-19339.0Tlog10pPdObar=8.55-23649.7TIn the Rh-O system, the Rh2O3 and RhO2 heat of formation were reassessed. The new enthalpy values are –79698 kJ·mol−1·at−1 and –80142 kJ·mol−1·at−1, respectively. The calculated Gibbs energy of formation of RhO2 and Rh2O3 can be expressed as ΔGfRhO2=-234.44+0.1751·T and ΔGfRh2O3=-389.51+0.2737·T (in kJ·mol−1), respectively.

Tetrabutyl Ammonium Salts of Keggin-Type Vanadium-Substituted Phosphomolybdates and Phosphotungstates for Selective Aerobic Catalytic Oxidation of Benzyl Alcohol

A series of tetrabutyl ammonium (TBA) salts of V-included Keggin-type polyoxoanions with W (TBA4PW11V1O40 and TBA5PW10V2O40) and Mo (TBA4PMo11V1O40 and TBA5PMo10V2O40) as addenda atoms were prepared using a hydrothermal method. These synthesized materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV-Vis diffuse reflectance (DRS UV-Vis), thermogravimetric analysis (TGA), CHN elemental analysis (EA), inductively coupled plasma spectrometry (ICP-MS), and N2 physisorption techniques to assess their physicochemical/textural properties and correlate them with their catalytic performances. According to FT-IR and DRS UV-Vis, (PVXW(Mo)12−XO40)(3+X)− anions are the main species present in the TBA salts. Additionally, CHN-EA and ICP-MS revealed that the desired stoichiometry was obtained. Their catalytic activities in the liquid-phase aerobic oxidation of benzyl alcohol to benzaldehyde were studied at 5 bar of O2 at 170 °C. Independently of the addenda atom nature, the catalytic activity increased with the number of V in the Keggin anion structure. For both series of catalysts, TBA salts of polyoxometalates with the highest V-substitution degree (TBA5PMo10V2O40 and TBA5PW10V2O40) showed higher activity. The maximum benzyl alcohol conversions obtained were 93% and 97% using (TBA)5PMo10V2O40 and (TBA)5PW10V2O40 as catalysts, respectively. In all the cases, the selectivity toward benzaldehyde was higher than 99%.

Chemical Recycling of Polystyrene to Valuable Chemicals via Selective Acid-Catalyzed Aerobic Oxidation under Visible Light.

Chemical recycling is one of the most promising technologies that could contribute to circular economy targets by providing solutions to plastic waste; however, it is still at an early stage of development. In this work, we describe the first light-driven, acid-catalyzed protocol for chemical recycling of polystyrene waste to valuable chemicals under 1 bar of O2. Requiring no photosensitizers and only mild reaction conditions, the protocol is operationally simple and has also been demonstrated in a flow system. Electron paramagnetic resonance (EPR) investigations and density functional theory (DFT) calculations indicate that singlet oxygen is involved as the reactive oxygen species in this degradation process, which abstracts a hydrogen atom from a tertiary C–H bond, leading to hydroperoxidation and subsequent C–C bond cracking events via a radical process. Notably, our study indicates that an adduct of polystyrene and an acid catalyst might be formed in situ, which could act as a photosensitizer to initiate the formation of singlet oxygen. In addition, the oxidized polystyrene polymer may play a role in the production of singlet oxygen under light.

New insights for the catalytic oxidation of cyclohexane to K-A oil

Au-based catalysts have been reported to be active in the cyclohexane oxidation to K-A oil, but they showed some limitiations in terms of productivity, selectivity and required reaction conditions. The possibility to overcome some of these limits has been explored coupling Au with Cu, which can be suitable for undergoing the electron-switch in the initial step of the cyclohexane oxidation. Hence, a bimetallic 2 wt% AuCu/Al2O3 catalyst was tested in the oxidation of cyclohexane, working at mild conditions of 120 °C and 4 bar of O2. The combination of the catalyst with a very small amount of benzaldehyde used as cheaper and non-toxic radical initiator allowed to obtain a very high productivity of cyclohexanol and cyclohexanone (45 mmol*mL/mgmet*h) with a selectivity of 94%. Moreover, comparing the catalysed reaction with the non-catalysed one, the role of the catalyst has been disclosed.

Synthesis, Crystal Structure of Tetra-Nuclear Macrocyclic Zn(II) Complex and Its Application as Catalyst for Oxidation of Benzyl Alcohol

A new six coordinated tetra-nuclear macrocyclic Zn(II) complex, ZnL4(Phen)2 (1) (HL= 3-bromo-2-hydroxybenzaldehyde-pyridine-2-carbohydrazone, Phen = 1,10-phenanthroline) has been synthesized by the self-assembly of 3-bromo-2-hydroxybenzaldehyde-pyridine-2-carbohydrazone, Zn(CH3COO)2•2H2O, NaOH and 1,10-phenanthroline in water/ethanol (v:v = 1:3) solution. Complex 1 was characterized by elemental analysis, infra red (IR), and single-crystal X-ray diffraction (XRD) analysis. The results show that Zn1 and Zn1b ions are six-coordinated with a distorted octahedral geometric configuration by four O atoms of two different L ligands and two N atoms of two different L ligands, Zn1a and Zn1c ions are also six-coordinated with a distorted octahedral geometric configuration by two N atoms of two different L ligands, two N atoms of Phen ligands and two O atoms of two different L ligands. Complex (1) forms 3D network structure by the - interaction. The selective oxidation reactions of benzyl alcohols catalyzed by complex (1) was investigated. The highest benzyl alcohol conversion and benzaldehyde selectivity were obtained at 100 °C for 4 h under 5 bar of O2. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Study of the oxidative esterification of furfural catalyzed by Au25(glutathione)18 nanocluster deposited on zirconia

Au/ZrO2 catalyst prepared from Au25(SG)18 nanoclusters (SG stands for glutathione) deposited on ZrO2 has shown to be an efficient system for the oxidative esterification of furfural with methanol. The influence of the supported nanoclusters was studied and showed that partial calcination of the supported nanoclusters at 300 °C was sufficient for a quantitative formation of methyl-2-furoate even in the absence of a base. In the presence of 0.27 mol% of Au, initial activities up to 250 h−1 were obtained at 100 °C under 6 bar of O2. The reactivity was extended to the oxidative esterification of furfuryl alcohol and the formation of various products and intermediates was discussed.

Heterogeneous Bimetallic Cu–Ni Nanoparticle-Supported Catalysts in the Selective Oxidation of Benzyl Alcohol to Benzaldehyde

Three bimetallic Cu–Ni nanoparticle-supported catalysts were synthesized by co-immobilization followed by H2 reduction. A chromium(III) terephthalate metal organic framework (MIL-101), titanium dioxide (TiO2), and carbon (C) with different properties (acidity and Brunauer–Emmett–Teller surface area) were selected as supports for studying the effect of the support nature on the catalytic activity and selectivity in the oxidation of benzyl alcohol. The physicochemical properties of the Cu–Ni-supported catalysts were characterized by XRD, NH3-TPD, nitrogen adsorption/desorption, TEM, EDS, XPS, and ICP-OES. Bimetallic Cu–Ni nanoparticles were highly dispersed on the support. The catalytic activities of CuNi/MIL-101, CuNi/TiO2, and CuNi/C were tested in the selective oxidation of benzyl alcohol to benzaldehyde in the presence of molecular oxygen under mild reaction conditions. The highest benzaldehyde yields were achieved with CuNi/TiO2, CuNi/MIL-101, and CuNi/C catalysts at 100 °C within 4 h under 5, 3, and 3 bar of O2, respectively. The bimetallic Cu–Ni-supported catalysts possessed two types of catalytic active sites: acid sites and bimetallic Cu–Ni nanoparticles. The CuNi/MIL-101 catalyst possessed a high number of acid sites and exhibited high yield during selective benzyl alcohol oxidation to benzaldehyde. Importantly, the catalysts exhibited a high functional group (electron-donating and electron-withdrawing groups) tolerance. Cu–Ni-supported catalysts with an Cu:Ni mole ratio of 1:1 exhibited the highest yield of 47% for the selective oxidation of benzyl alcohol to benzaldehyde. Reusability and leaching experiment results exhibited that CuNi/MIL-101 showed better stability than CuNi/TiO2 and CuNi/C catalysts due to the large porous cavities of MIL-101 support; these cavities can be used to trap bimetallic Cu–Ni nanoparticles and inhibit nanoparticle leaching.

Catalytic cyclohexene oxidation in the nano channels of a copper silicate material

Herein we examined the catalytic activity of the copper silicate material SGU-29 for the aerobic partial oxidation of cyclohexene under mild conditions (1 bar of O2 at 70 °C). In particular, the catalytic properties of the active sites provided by [CuO4] square planar units in SGU-29 were investigated for cyclohexene oxidation to generate three main oxidation products (i.e., 2-cyclohexene-1-ol, 2-cyclohexene-1-one, and cyclohexene hydroperoxide). Based on the molecular sieving effect of SGU-29, we especially investigated the intrazeolitic reaction, a catalytic cyclohexene oxidation occurring only in nanochannels of SGU-29. A conversion yield of 42% was obtained for the aerobic cyclohexene oxidation occurring only in SGU-29 nanochannels under 1 bar of O2 at 70 °C for 12 h. We demonstrated unequivocally that catalysis occurred only within the inner channels of SGU-29, rather than on its external surface or within the solvent, and we highlighted the special role of [CuO4] square planar units in catalysis.

Gold Supported on Strontium Surface-Enriched CoFe2O4 Nanoparticles: a Strategy for the Selective Oxidation of Benzyl Alcohol

The synthesis of efficient and reusable gold-based catalysts for the selective oxidation of alcohols is a strategy for the development of green processes. Pre-formed nanoparticles syntheses are an easy way to produce controlled-nanosized gold materials; however, the selection of a support is not trivial. Herein, we proposed a CoFe2O4 support enriched with Sr(OH)2, which holds remarkable properties and is suitable for the synthesis of a stable gold-based catalyst for the oxidation of benzyl alcohol. We suggested that the interaction between the CoFe2O4 and the Sr(OH)2 is highly important for the performance of the catalyst. Under the base-free condition of 2.5 h, 100 oC and 2 bar of O2, the catalyst reached 58% of conversion with 76% of selectivity to benzaldehyde. With K2CO3 addition, the conversion and selectivity to benzaldehyde increased to 87% and 88%, respectively. Any gold leaching was detected in 5 successive runs, attesting the noticeable stability that the catalyst presents. This work provides great potential for the selective oxidation of alcohols with high activity since the magnetic properties of the catalyst provide an easy route and allows the separation of the medium reaction. In addition, we are here proposing an important interaction between the Sr(OH)2 and the magnetic nanoparticles.

Aerobic Oxidation of Benzyl Alcohol on a Strontium-Based Gold Material: Remarkable Intrinsic Basicity and Reusable Catalyst

The development of stable and active gold catalysts has arisen as a significant strategy for oxidation of alcohols. Nano-size PVA-stabilized gold nanoparticles immobilized on Sr(OH)2 by colloidal deposition presented high catalytic activity for benzyl alcohol oxidation. In 2.5 h, 2 bar of O2 and without extra-base addition, the calcined support reached 54.6% (100 °C) and 67.4% (140 °C) of conversion, presenting the remarkable and unexplored intrinsic basicity that strontium-based materials retain. With sub-stoichiometric K2CO3 adding, under the same catalytic conditions, the catalyst conducted the reaction with similar activity, but with excellent reusability in the process, without any gold leaching. We investigated the influence that the support synthesis method and the solvent used for the NPs stabilization have on the oxidation activity. The produced materials were fully characterized by XPS, Rietveld refinement, and TEM.

Reactions Catalysed by a Binuclear Copper Complex: Aerobic Cross Dehydrogenative Coupling of N-Aryl Tetrahydroisoquinolines.

Binuclear copper complex [{Cu(Sal)2 (NCMe)}2 ] (Sal=salicylate) was found to be an active catalyst for the aerobic oxidation of N-aryl tetrahydroisoquinolines to the corresponding iminium ions, which could be trapped by a wide range of nucleophiles to form coupled products. The reactions took place under 1 bar of O2 at room temperature with 1 mol % of the copper catalyst being sufficient in most cases, and are considerably accelerated by catalytic chloride anions. Mechanistic studies show that the CuII dimer oxidizes the amine to the iminium ion, and this two-electron process requires O2 , whereby the resulting CuI is concomitantly reoxidised back to CuII . Various lines of evidence suggest that the oxidative coupling reaction is turnover-limited by the step of iminium formation, and it is this step that is promoted by the chloride anion. Since it is more efficient than and mechanistically distinct from the well-studied simple copper salts such as CuBr and CuCl2 , the binuclear copper catalyst provides a new tool for oxidative coupling reactions.

ChemInform Abstract: A Convenient Procedure for the Oxidative Dehydrogenation of N‐Heterocycles Catalyzed by FeCl2/DMSO.

A convenient catalytic procedure has been developed for the oxidative dehydrogenations of N-heterocycles. Combining catalytic FeCl2 with DMSO yields a catalyst that promotes the dehydrogenation of tetrahydroquinolines and related heterocycles under 1 bar of O2, affording the corresponding N-heteroaromatic products in moderate yields.

A Convenient Procedure for the Oxidative Dehydrogenation of N-Heterocycles Catalyzed by FeCl2/DMSO

A convenient catalytic procedure has been developed for the oxidative dehydrogenations of N-heterocycles. Combining catalytic FeCl2 with DMSO yields a catalyst that promotes the dehydrogenation of tetrahydroquinolines and related heterocycles under 1 bar of O2, affording the corresponding N-heteroaromatic products in moderate yields.

Continuous, Fast, and Safe Aerobic Oxidation of 2-Ethylhexanal: Pushing the Limits of the Simple Tube Reactor for a Gas/Liquid Reaction

A continuous-flow microreactor is applied for the selective aerobic neat oxidation of 2-ethylhexanal. Under 7.5 bar of O2 and 10 ppm of Mn(II) as catalyst, a production of up to 130 g/h of 2-ethylhexanoic acid can be obtained with a PFA tubing of 7 m (O 1.65 mm, reactor volume ca. 15 mL). The synergistic use of alkali metal salts and Mn(II) as catalyst improve the selectivity up to 94% under those conditions. We show that the productivity of this simple tube microreactor is limited by the thermal management.

Chemical Wet Oxidation for the Abatement of Refractory Non-Biodegradable Organic Wastewater Pollutants

Various chemical wet oxidation techniques to remove toxic non-biodegradable pollutants from wastewater were compared in this work. Techniques applied included catalytic wet air oxidation (CWAO) over active carbon (AC) alone and with hydrogen peroxide (H2O2) as well as wet peroxide oxidation (WPO) without or plus Fe2+ initiator. The oxidation tests were conducted in a Trickle Bed Reactor and a tubular coil reactor at 25–550°C and 10–150 bar. The refractoriness to chemical wet oxidation was investigated for various organic pollutants including phenol, o-cresol, m-xylene, o-chlorophenol, p-nitrophenol, aniline, nitrobenzene, sulfolane and two industrial phenolic wastewater. CWAO over AC destroyed readily phenol, o-cresol, m-xylene and o-chlorophenol at 140°C and 9 bar of O2. More refractory aniline, p-nitrophenol, and particularly sulfolane and nitrobenzene, were tested with either H2O2 promoted CWAO or WPO at higher temperatures. The use of Fe2+ initiator was attempted to reduce the treatment severity of WPO. In a final step, the wet oxidation techniques were tested on the industrial effluents to obtain treatment efficiencies under field conditions.

Thermodynamic Assessment of the Ca‐Cu‐O System

The experimental data on the Ca‐Cu‐O system at 1 bar total pressure have been reviewed and an optimized thermodynamic description based on previous assessments of the binary systems is presented. Three ternary oxides are found which do not show significant solid solution and have been treated as stoichiometric compounds. The liquid exhibits a miscibility gap as in the Cu‐O binary. Only the copper oxide liquid extends into the ternary field and has been modeled with ternary parameters. A continuous thermodynamic description of the liquid phase from the metal to the oxide part has been obtained using the two‐sublattice ionic liquid model. The set of optimized parameters leads to a consistent and accurate thermodynamic description of the Ca‐Cu‐O system at 1 bar total pressure. Calculated CaO‐CuOx phase diagrams in air and 1.01 bar of O2, an oxygen potential diagram, an isothermal section at 1573 K, and various thermodynamic properties are shown and compared with experimental data. In particular the relative amounts of Cu+ and Cu2+ in the oxide liquid have been calculated in air and 1.01 bar of O2.