Selective Oxidation Process Research Articles

Nature of Reactive Sites in TS-1 from 15N Solid-State NMR and Ti K-Edge X-Ray Absorption Spectroscopic Signatures Upon Pyridine Adsorption.

Ti-containing zeotypes, notably titanosilicalite-1 (TS-1), are prominent examples of heterogeneous catalysts that have found applications in selective oxidation processes with hydrogen peroxide. Despite extensive characterization studies including using various probe molecules to interrogate the nature and the local environment of Ti sites, their detailed structure (as well as reactivity) remains elusive. Here, we demonstrate that using low temperature 15N magic angle spinning (MAS) ssNMR spectroscopy of adsorbed pyridine on TS-1 combined with Ti K-edge XANES on a range of samples (dehydrated, hydrated, contacted with H2O2 and pyridine) provides unique information regarding the Ti sites, highlighting their reactivity and dynamic nature. While dehydrated TS-1 shows only Lewis acid sites, the presence of H2O generates Brønsted acid sites, whose amount correlates with water loading. Moreover, the methodology─based on 15N ssNMR and Ti K-edge XANES─applied to a library of samples with various Ti-loadings and absence of extraframework TiO2 also enables quantification of the amount of Lewis acid sites and to establish a structure-activity descriptor (ratio of pyridine adsorbed on silanols vs titanium). Complementary analysis including computational modeling reveals that the reaction of Ti sites with H2O generates an acidic bridging silanol Ti-(OH)-Si, upon hydrolysis of one Ti-O-Si linkage, where Ti expands its coordination from four to pentacoordinated according to XAS.

Comprehensive extraction of V, Ni and Mo from black shale via selective leaching oxidation process

Black shale is one of the most representative sources of vanadium, nickel and molybdenum in China. Due to the poor endowment of minerals in black shale, V, Ni, Mo and other metals complex co-associated endowment state, extraction is difficult and long-term unused, resulting in a significant waste of resources. In this paper, it is shown that V, Ni and Mo can be obtained from black shale by a stepwise oxidation leaching process. In a first leaching process, V and Ni are effectively leached simultaneously. Mo is left in the residue. The leaching efficiency of V, Ni and Mo was 86.81%, 89.19% and 5.80% respectively under the leaching conditions of 35wt.% H2SO4, 4wt.% CaF2, 1.2:1 liquid to solid ratio (L/kg), 95℃ and 8h. The residue was then leached twice. The leaching efficiency of molybdenum was 91.10% under the leaching conditions of 25wt.% H2SO4, 8wt.% NaClO3, 1.5:1 liquid to solid ratio (L/kg), 45℃ and 7h. V2O5 products have been successfully prepared, the purity of V2O5 reaches 98.34%. A stepwise oxidation leaching method has been proposed to separate the vanadium, nickel and molybdenum in the leaching process. Vanadium, nickel and molybdenum can be effectively extracted from the black shale by the stepwise oxidation leaching process to maximize the utilization of the resources.

A Green and Efficient Electrocatalytic Route for the Highly-Selective Oxidation of C-H Bonds in Aromatics over 1D Co3O4-Based Nanoarrays.

Electrocatalytic oxidation of C-H bonds in hydrocarbons represents an efficient and sustainable strategy for the synthesis of value-added chemicals. Herein, a highly selective and continuous-flow electrochemical oxidation process of toluene to various oxygenated products (benzyl alcohol, benzaldehyde, and benzyl acetate) is developed with the electrocatalytic membrane electrodes (ECMEs). The selectivity of target products can be manipulated via surface and interface engineering of Co3O4-based electrocatalysts. We achieved a high benzaldehyde selectivity of 90% at a toluene conversion of 47.6% using 1D-Co3O4 nanoneedles (NNs) loaded on a microfiltration (MF) titanium (Ti) membrane, i.e, Co3O4 NNs/Ti. In contrast, the main product shifted to benzyl alcohol with a selectivity of 90.1% at conversion of 32.1% after modifying MnO2 nanosheets (NSs) on Co3O4 NNs/Ti (Co3O4@MnO2/Ti) catalyst. Moreover, benzyl acetate product can be obtained withselectivity of 92% at a conversion of 58.5% at high current density (> 1.5mA cm-2), demonstrating that the pathway of toluene oxidation is readily maneuvered. DFT results reveal that modifying MnO2 on Co3O4 optimizes the electron structure of Co3O4@MnO2/Ti and modulates the adsorption behavior of intermediate species. This work demonstrates a sustainable,and continuous-flow process for precise control over production selectivity of value-added oxygenated derivatives in electrochemical oxidation of aromatic hydrocarbons.

Partial oxidation of cyclohexene over histidine-modified Cu-UiO-66 under aerobic conditions

Enzyme-inspired catalysis is an attractive approach for developing selective hydrocarbon partial oxidation processes. Here, histidine was introduced into defective UiO-66 metal–organic framework by ligand exchange, followed by Cu(II) ion insertion. Density functional theory modeling combined with X-ray Absorption spectroscopy revealed that Cu(II) has a higher affinity for open Zr-O node sites than for histidine, leading to a series of materials where Cu(II) ions are predominantly anchored to the Zr6O4(OH)4 nodes, while only minority fractions of Cu(II) are anchored to histidine. Catalytic testing for aerobic cyclohexene oxidation with tert-butyl hydroperoxide (t-BuOOH) in trifluorotoluene solution at 25 °C showed activity for cyclohexene oxidation to cyclohexenol and cyclohexenone, with high selectivity. Benchmark tests revealed that Cu and t-BuOOH are both essential for the reaction, yet t-BuOOH consumption was far inferior to product formation rates, suggesting a radical reaction pathway involving O2.

Development of a Rotating Disk Electrode-Based Ru-Leaching AST for PEM Fuel Cell Reformate Anode Ru-Pt/C Catalysts

Extreme heavy-duty (e.g., maritime) applications of PEM fuel cells often require liquid hydrogen carriers as fuel.[1] In the case of methanol, it is mixed with steam and converted to hydrogen and CO2 in a catalytic reformation process.[2] While a multi-step approach, including the water-gas shift reaction and selective oxidation processes, is typically undertaken to fully convert methanol to hydrogen and CO2, low ppm-level amounts of CO remain in the resulting “reformate hydrogen” gas stream.[3] This CO concentration is significantly higher than deemed non-poisonous to the platinum catalyst on the anode (i.e., < 0.2 ppm),[4] and a more CO-tolerant anode catalyst is required. To address this issue, RuPt-alloy nanoparticles supported on carbon are employed, leading to CO-tolerance of the HOR-catalysts on the anode at reformate conditions.[3] However, previous works found that during operation, Ruthenium leaches from the anode catalyst layer and travels through the membrane, subsequently depositing on the platinum nanoparticles, effectively poisoning the cathode Pt/C catalyst and significantly reducing its activity towards the oxygen reduction reaction.[3,5] To eliminate or reduce Ru-leaching from RuPt/C catalysts while retaining its inherent CO-tolerance, efforts tuning the catalyst’s (surface) composition were made. However, as the leaching of Ru in fuel cells occurs over thousands of hours, the use of an accelerated stress test (AST) for reformate anodes is required. In one of our previous efforts, an AST for Ru-leaching in fuel cells was used to study RuPt/C degradation.[3] However, the amount of material, MEA preparation time and AST measurement time required for such a test was found to be too high for catalyst development. Additionally, fuel cell measurement capacity is limited due to its high cost and the quantification of the total amount of Ru-leached remained challenging.In light of this, in this work, we developed an AST aimed at achieving a reliable yet short and less material consuming protocol, enabling us to quantitatively investigate the Ru-leaching of RuPt-materials during catalyst development. This was achieved by using the rotating disk electrode (RDE) configuration, a well-established electrocatalyst characterization and pre-testing method.[6] The RDE-based AST-protocol was developed using three commercial RuPt-catalysts with varying Ru:Pt ratios of 1:1, 1.5:1, and 2:1 while possessing a comparable particle size and electrochemical surface area. Additionally, the commercial catalyst with a 2:1 atomic ratio catalyst was used in a heat-treated form leading to a larger particle size and lower ECSA.The AST-protocol was comprised of a series of voltammetric cycles aimed at aging the catalyst. During the protocol development, the number of aging cycles (100 – 1000), the scan rate (10 – 100 mV s-1), and the upper inversion potential (0.8 – 0.9 VRHE) of the cyclic voltammograms were varied to investigate their influence on catalyst degradation. This was achieved by collecting the electrolyte (Ar-saturated 0.1M H2SO4) after the AST-cycles and subsequent quantification of the dissolved Ru using inductively coupled plasma optical emission spectroscopy (ICP-OES). Furthermore, the change in the surface composition was qualitatively analyzed by comparing the CO-oxidation peak shape and position before and after the AST-cycling. Examples of the ICP-OES and CO-stripping results for the systematic investigation of the influence of cycle number and scan rate on the 1.5:1 Ru:Pt catalyst using an upper inversion potential of 0.85 VRHE are displayed in Figure 1. Based on this rigorous investigation of the parameters influencing Ru-dissolution in an RDE-environment and after the necessary validation of the results found using the finalized protocol in MEA-based testing,[5] the developed protocol could subsequently be applied to self-synthesized RuPt/C materials as well as RucorePtshell-catalysts.In summary, this contribution showcases the development of a reliable rotating disk electrode-based accelerated stress test protocol for Ru-leaching from RuPt/C catalysts. Furthermore, its validation with commercial catalysts as well as its application to self-synthesized PEM fuel cell anode catalysts for use with reformate hydrogen, is presented.

PolyBorylated Alkenes as Energy-Transfer Reactive Groups: Access to Multi-Borylated Cyclobutanes Combined with Hydrogen Atom Transfer Event.

While polyborylated alkenes are being recognized for their elevated status as highly valuable reagents in modern organic synthesis, allowing efficient access to a diverse array of transformations, including the formation of C-C and C-heteroatom bonds, their potential as energy-transfer reactive groups has remained unexplored. Yet, this potential holds the key to generating elusive polyborylated biradical species, which can be captured by olefins, thereby leading to the construction of new highly-borylated scaffolds. Herein, we report a designed energy-transfer strategy for photosensitized [2+2]-cycloadditions of poly-borylated alkenes with various olefins enabling the regioselective synthesis of diverse poly-borylated cyclobutane motifs, including the 1,1-di-, 1,1,2-tri-, and 1,1,2,2-tetra-borylated cyclobutanes. In fact, these compounds belong to a family that presently lacks efficient synthetic pathways. Interestingly, when α-methylstyrene was used, the reaction involves an interesting 1,5-hydrogen atom transfer (HAT). Mechanistic deuterium-labeling studies have provided insight into the outcome of 1,5-hydrogen atom transfer process. In addition, the polyborylated cyclobutanes are then demonstrated to be useful in selective oxidation processes resulting in the formation of cyclobutanones and γ-lactones.

PolyBorylated Alkenes as Energy‐Transfer Reactive Groups: Access to Multi‐Borylated Cyclobutanes Combined with Hydrogen Atom Transfer Event

AbstractWhile polyborylated alkenes are being recognized for their elevated status as highly valuable reagents in modern organic synthesis, allowing efficient access to a diverse array of transformations, including the formation of C−C and C‐heteroatom bonds, their potential as energy‐transfer reactive groups has remained unexplored. Yet, this potential holds the key to generating elusive polyborylated biradical species, which can be captured by olefins, thereby leading to the construction of new highly‐borylated scaffolds. Herein, we report a designed energy‐transfer strategy for photosensitized [2+2]‐cycloadditions of poly‐borylated alkenes with various olefins enabling the regioselective synthesis of diverse poly‐borylated cyclobutane motifs, including the 1,1‐di‐, 1,1,2‐tri‐, and 1,1,2,2‐tetra‐borylated cyclobutanes. In fact, these compounds belong to a family that presently lacks efficient synthetic pathways. Interestingly, when α‐methylstyrene was used, the reaction involves an interesting 1,5‐hydrogen atom transfer (HAT). Mechanistic deuterium‐labeling studies have provided insight into the outcome of 1,5‐hydrogen atom transfer process. In addition, the polyborylated cyclobutanes are then demonstrated to be useful in selective oxidation processes resulting in the formation of cyclobutanones and γ‐lactones.

Radical-driven selective oxidation of benzyl alcohol on MnCoOx catalysts with no oxidant other than air in reactor

Mn reinforced Co3O4 catalysts (MnCoOx) were prepared by a facile solid phase mixed foaming method with an in-situ heating enhancement for the formation of spinel phase mixed oxide species, and studied in the selective oxidation of benzyl alcohol just the air in reactor as oxygen donor. It was found that the MnCoOx catalysts are composed of relatively minimal spinel MnCo2O4 mixed oxide and massive Co3O4 to form MnCo2O4-Co3O4 oxide pair. The micro-domains of MnCo2O4-Co3O4 oxide pair present two redox couples of Mn3+/Mn2+ and Co3+/Co2+ instead of the single one of Co3+/Co2+ in Co3O4, and then dramatically enhance the formation of superoxide radicals (•O2–) species from the O2 in air, which can efficiently initiate the conversion of benzyl alcohol to benzaldehyde in a Fenton-like processes. With no oxidant other than air in reactor, the interaction between MnCo2O4 and Co3O4 in MnCoOx catalysts leads to a benzyl alcohol conversion up to 98 % with a 100 % benzaldehyde selectivity at atmospheric pressure while single component Co3O4 can only present a benzyl alcohol conversion at 37 %. This embodiment of highly efficient heterogeneous selective oxidation just with air as oxidant provides a probability for developing a low-cost and super-facile radical-induced selective oxidation process for alcohols.

THE ROLE OF QUANTUM CHEMICAL CALCULATIONS IN CATALYSIS: A REVIEW

The article talks about the high role of quantum chemical research methods in such a promising direction as the catalytic oxidation of saturated hydrocarbons, especially in the study of transition states of molecules. Theoretical analysis is based on research in catalysis and computational chemistry. Computational chemistry is an effective tool that allows one to calculate the structure and physical properties of catalysts, as well as the structure and energy of the activated complex. In this review, special attention is paid to identifying a sufficiently accurate and, at the same time, less energy-consuming method for determining the structure of the transition state. The most popular methods of quantum chemical calculations are presented, among which a special role is given to density functional theory (DFT), functionals B3LYP, OLYP, PBE and basis sets 6-31G, LANL2DZ. The use of machine learning by some authors, along with quantum chemical computing, to identify catalysts for activation and functionalization of C-H bonds has been mentioned. The advantages and disadvantages of computational chemistry for heterogeneous catalysis are discussed. The results of studies of catalysts predicated on transition metal complexes are summarized. It is underlined that nanocomposites based on transition metals attract the attention of researchers due to their d-orbitals, which are responsible for the reactivity when activating C-H bonds. The review also indicates plans for conducting quantum chemical calculations to study the catalytic processes of selective oxidation of n-alkanes using tran-sition metal nanocomposites as catalysts. This review will be useful for future applications of computational chemistry methods for the development of new catalysts and the study of chemical reaction mechanisms

Role of the catalyst structure–activity relationship in enhancing the selective oxidation yield of n-butane to maleic anhydride

Vanadium phosphorus oxide (VPO) catalysts are synthesized for utilization of lighter alkanes such as n-butane to produce maleic anhydride (MA) by a selective oxidation process.

Catalytic NH3 oxidation affected by the nanometric roughness of the platinum overlayer.

Pulsed cathodic arc-plasma deposition was employed to create a few nanometre-thick Pt overlayer on a 50 μm-thick Fe-Cr-Al metal (SUS) foil, resulting in an effective NH3 oxidation catalyst fabrication. This catalyst exhibited a turnover frequency (TOF) exceeding 100 times that of Pt nanoparticles. In this study, Pt overlayer catalysts with varying degrees of surface roughness were fabricated using different metal foil substrates: mirror-polished (Pt/p-SUS), unpolished (Pt/SUS) and roughened by the formation of a surface oxide layer (Pt/Al2O3/SUS). The nanoscale roughness was comprehensively analysed using electron microscopy, laser scanning confocal microscopy and chemisorption techniques. NH3 oxidation activity, measured at 200 °C, followed an increasing trend in the order of Pt/Al2O3/SUS < Pt/SUS < Pt/p-SUS, despite a decrease in the apparent Pt surface area in the same order. Consequently, the calculated TOF was markedly higher for Pt/p-SUS (267 min-1) compared to Pt/SUS (107 min-1) and Pt/Al2O3/SUS (≤22 min-1). The smooth Pt overlayer surface also favoured N2 yield over N2O at this temperature. This discovery enhances our fundamental understanding of high-TOF NH3 oxidation over Pt overlayer catalysts, which holds significance for the advancement and industrial implementation of selective NH3 oxidation processes.

Operando X-Ray Diffraction Studies of Co Oxide Model Catalysts during Alcohol Oxidation and Oxygen Evolution Reaction

Green energy technology involving hydrogen generation requires developing catalyst materials of commercial viability, good stability and high reactivity for the electrochemical water splitting. Transition-metal oxides such as Co3O4 are among the best precious-metal-free electrode materials for the anodic oxygen evolution reaction (OER) in alkaline electrolysis [1]. Moreover, these spinel-type transition metal oxides are an important class of catalysts for the selective oxidation of organic compounds. Previous in situ and operando surface X-ray diffraction studies of epitaxial Co oxide films by our group showed pronounced changes in the near-surface structure of these catalysts. In particular, a sub-nm CoOx(OH)y skin layer starts forming in the pre-OER potential range which is accompanied by a volume change of the Co3O4 lattice [2]. In a more recent work, where we systematically explored the relationship between the effective thickness of this skin layer and the OER activity, we found clear evidence that the entire skin layer serves as a three-dimensional reactive zone for the OER [3]. Since the skin layer formation already starts several 100 mV negative of the onset of the OER, it is not induced by the catalytic reaction itself, but rather reflects the oxides’ electrochemistry, and may thus be expected also for other electrocatalytic processes, especially other electrocatalytic oxidation reactions which occur in a similar potential range. These oxide materials are not only of interest for OER, but also for the electrochemical oxidation of other compounds, such as alcohols [4]. However, data on the oxides’ structure in the presence of organic compounds does not exist at present. Obtaining such data is of great interest for understanding the mutual influence of oxide-electrolyte interface structure and electrocatalytic activity. In addition, the vast majority of publications on Co oxide oxidation processes, in particular all in situ and operando studies, have been performed up to now at room temperature only, and, thus, the catalytic performance of these materials at higher temperatures remains unknown. As electrolyzers and industrial (electro-) catalytic processes typically operate at elevated temperatures, such data are of considerable interest. Here, we present results of first potential-dependent structural studies of epitaxial Co3O4(111) and CoOOH(001) films electrodeposited on Au(111) single crystal substrates during ethylene glycol oxidation (EG Ox) in 0.1 M NaOH solution and compare those with the behavior found on the same samples in EG-free electrolyte. Ethylene glycol oxidation is a highly suitable reaction for such studies, as it occurs at potentials prior to the onset of the OER [4]. The samples were investigated as a function of electrode potential and temperature by operando surface X-ray diffraction at beamline P23 of PETRA III, DESY. The EG Ox was studied by successively increasing the EG concentration from 0 to 0.1, 0.5 and 2 M, which allows direct quantitative comparison of the potential-dependent structural changes. These studies of the oxides’ structure and electrochemical reactivity were performed at different temperatures in the range of 25 - 70°C. In all cases significant skin layer formation and accompanying changes in the oxide lattice strain were observed. The structural data are correlated with the results of cyclic voltammetry and optical reflectivity measurements that were recorded in parallel with the X-ray diffraction measurements. Together, they provide insights into the potential-dependent evolution of the skin layer thickness and strain and into the stability of the oxides in dependence of EG concentration and temperature. First results indicate that at elevated temperatures larger skin layer thicknesses and strain changes occur. Furthermore, the structural properties recover completely upon cooling back down to room temperature, suggesting that these effects are highly reversible. In the presence of EG, the reversible skin layer formation and changes in the Co3O4 bulk lattice were also observed, even though these structural changes appear to be less pronounced under alcohol oxidation conditions, especially at higher EG concentration. These studies will contribute to an in-depth understanding of the near surface structure of these Co oxide thin films during liquid phase oxidation catalysis, which is a prerequisite for the design of new, abundant and superior catalysts based on transition metal oxides for catalytic selective oxidation processes.We acknowledge financial support by the Deutsche Forschungsgemeinschaft via special research area TRR 247, project B10 (project no. 388390466).[1] A. Bergmann et al., Nature Catalysis 2018, 1, 711 - 719[2] F. Reikowski et al., ACS Catal. 2019, 9, 3811 - 3821[3] T. Wiegmann et al., ACS Catal. 2022 [4] S. N. Sun et al, J. Electrochem. Soc. 2016, 163, H99

Single atom manganese catalyst boosting selective oxidation of alcohols with activated peroxymonosulfate

Selective oxidations are important reactions in organic synthesis for fine chemical industry and conventional methods are expensive and produce a lot of toxic wastes. Herein, we demonstrate a facile and environmentally benign technique for liquid phase selective oxidation based on graphene-supported Mn single-atom-catalyst (SAMn-G) for efficient peroxymonosulfate (PMS) activation. The active Mn component in the developed SAMn-G catalyst reached single-atomic dispersion on graphene substrate via the coordination of individual Mn atoms with the doped N from the graphene framework. SAMn-G activated PMS via a nonradical-dominated pathway, which could convert aromatic alcohols into aldehydes or ketones at a mild temperature. The SAMn-G catalyst exhibited superior conversion and aldehyde selectivity in alcohol oxidation in comparison with their counterpart catalysts possessing either homogeneous Mn ions or oxide particles. The high activation efficiency of SAMn-G is due to the synergistic effect between Mn atoms and graphene substrate, as well as the dominated reaction pathway from nonradical oxidation, which is more selective than these free radicals to oxidize the alcohols. Concerted experimental evidence indicates that the non-radical oxidation process was highly possible to follow the electron transfer mechanism by PMS/organic adsorption on the surface of the catalyst. This study provides a fundamental understanding of PMS activation mediated by single atom catalyst for organic synthesis and the achieved insights can also help the catalyst design for other liquid phase selective oxidation processes.

Hierarchically porous, N-defect enriched C-nanosheets boost the H2S selective oxidation to elemental sulfur

H2S selective oxidation to elemental sulfur (S8) is a typical reaction where the mass product diffusion (e.g., S8) through the catalytic bed is crucial as well as the reagents accessibility (e.g., H2S, O2) to the active sites. The NaNO3-assisted pyrolysis of polyacrylamide was applied to synthesize defect-enriched N-doped carbon nanosheets with thickness up to c.a. 2 nm, featured by fully accessible and highly interconnected pores, for boosting the H2S selective oxidation process. The PAM-0.3-700 sample has revealed an unprecedented desulfurization activity with sulfur formation rate of 1165 gsulfur kgcat.−1 h−1, other than a remarkable stability (>80 h). Experimental and theoretical studies have unveiled the critical role of edge sites containing unpaired electrons and nitrogen species with respect to the material aptitude towards O2 dissociation and HS- activation. The material in presence of a highly interconnected porous network facilitates the reactants/product diffusion especially for catalysis operated under harsh experimental conditions.

Advances of Single‐Atomic Cobalt Catalysts in Liquid‐Phase Selective Oxidative Reactions

Single‐atom catalysts (SACs) composed of atomically dispersed metal‐active sites embedded in supporting substrates are attracting increasing attention in liquid‐phase selective oxidation reactions with joint merits of both advanced catalytic efficiency and high stability. Co‐based SACs present superior performance in several model oxidative reactions against many other metals, thus they are recognized as a promising solution to the current high‐cost noble‐metal catalysts required for the synthesis of fine chemicals. In this review, the up‐to‐date research on the synthesized Co–SACs in selective oxidation applications is summarized. The strategies of the preparation of Co–SACs with diverse Co‐loading levels and well‐tuned morphologies and chemical structures are showcased, as well as the characterization techniques of the SACs. The applications of Co–SACs in a series of selective oxidation reactions and the influence of different oxidants on the overall reaction efficiency are discussed. In addition, the progress of the mechanism exploration involving active‐site identification, catalytic activation of oxidants, and oxidation pathway elucidation is highlighted. Meanwhile, the existing challenges and the future efforts for the development of the Co–SAC reaction system in selective oxidation processes are outlined.

Effect of electromagnetic induction drying on the drying–incineration process of dyeing sludge: focus on migration and conversion of sulfur

Secondary sulfur pollution in dyeing sludge (DS) during drying and incineration is a major environmental problem necessitating in-situ control. To robustly immobilise sulfur during drying–incineration, the authors introduce an electromagnetic induction (EMI) drying method and reveal the corresponding migration and conversion of sulfur in DS. The EMI-drying efficiency reached 10.69%/min, five times that of thermal drying. EMI drying increases the relative sulfoxide ratio from that of thermal drying. In a sludge–sulfur model, the proposed treatment promoted the oxidation and decomposition of organic sulfur without noticeably affecting the inorganic sulfur. The selective oxidation process during EMI drying promotes sulfur stabilisation in dried DS, decreasing the performance and stability of DS combustion. The sulfur-containing pollutants released during the incineration of DS mainly contain H2S, followed by CH3SH and SO2. EMI drying increases the outputs of SO2 and CH3SH but decreases the outputs H2S and total sulfur compared with the outputs of thermal drying. Under the sulfur-model conditions, EMI promoted the conversion of inorganic sulfur to sulfur-containing gases (especially H2S) during incineration. In contrast, the sulfur stabilised by partial oxidation of organic sulfur in the EMI-dried DS was not easily converted to gaseous sulfur during subsequent combustion. Overall, EMI inhibits the release of sulfur during the combined drying–incineration process of DS.

Se-Doped Porous Carbon Supported Pt to Boost Selective Oxidation of Ethylene Glycol to Glycolic Acid

Biomass-derived polyols can be reformed to value-added chemicals by electrochemical selective oxidation process. Ethylene glycol (EG) and glycerol (GLY) are produced in a large surplus, hence rational design of electrocatalysts for efficient selective oxidation of these biomass-derived molecules should be required to utilize the EG and GLY. Various organic acids such as glycolic acid (GCA), oxalic acid (OXA) and formic acid (FA) can be produced in the oxidation pathway of EG.[1] In particular, EG selective oxidation targeted at the production of GCA, which has broad applications in skin care, textile industry and adhesives. Herein, we fabricated heteroatom doped porous carbons as support materials of highly dispersed Pt nanoparticles and applied to selective oxidation of EG to GCA. By introducing Se in carbon materials, the highly selective production of GCA was achieved with significant conversion of EG over 90%. The porous structure of carbon support led to well dispersed Pt nanoparticle and this morphology was observed by SEM and TEM. XPS and Raman analyses revealed that doped Se atoms changed electronic properties of carbon materials and induced defects into the carbon lattice structure. These properties greatly enhanced the electrocatalytic activity and stability of Pt/SePC, resulting that GCA yield reached to and remained around 85% during several repeated tests for the EG selective oxidation. Our study could highlight favorable strategy of catalyst design with heteroatom doping for ethylene glycol conversion to glycolic acid.[1] D. Jang, H. Han, J. Maeng, W. Yoon, M. Park and W. B. Kim, Highly active PdSb catalysts on porous carbon for electrochemical oxidation reactions of biomass-derived C1–C3 alcohols, Mater. Adv., 2022, 3, 5964-5973.

Efficient aerobic oxidation of alcohols and sulfides using an M-doped (M: Mn and Ni) zinc oxide nanostructure

The generation of aldehydes and sulfoxides through selective oxidation process plays an essential role in different organic synthesis. However, using or toxic solvents under harsh reaction conditions leads to wastes and undesired by-products. With this background, ultrafast one-step fabrication of Ni/Mn doped-ZnO was developed under ultrasonic agitation for the first time. The resulting nanostructure was characterized by XRD, SEM, TEM, and BET analysis. According to data, a single-phase ZnO structure (wurtzite type) with uniform morphology, and acceptable surface area was obtained for the prepared nanocatalyst. Next, the catalytic activity of the nanostructure was investigated in aerobic oxidation of aliphatic and benzylic alcohols and sulfides. Notably, the present work is the first report of using ultrasound-engendered Ni/Mn doped-ZnO for selective aerobic oxidation reactions. It was found that the proposed nanostructure represented a novel chemical function for catalyzed alcohols and sulfides oxidation with excellent yields and selectivity without using any additives.

Activation of peroxymonosulfate by Fe–Mn-modified MWCNTs for selective decontamination: Formation of high-valent metal-oxo species and superoxide anion radicals

The extensive presence of organic micropollutants in complex water matrices requires the development of selective oxidation technologies. In this study, a novel selective oxidation process was developed via the conjunction of FeMn/CNTs with peroxymonosulfate and successfully used to remove micropollutants such as sulfamethoxazole (SMX) and bisphenol A from aqueous solutions. FeMn/CNTs were prepared using a facile co-precipitation method, characterized using a series of surface characterization techniques, and then tested for pollutant removal. The results showed that the FeMn/CNTs had much greater reactivity than CNTs, manganese oxide, and iron oxide. The pseudo-first-order rate constant with FeMn/CNTs was more than 2.9–5.7 times that of the other tested materials. The FeMn/CNTs had great reactivity in a wide range of pH values from 3.0 to 9.0, with the best reactivity found at pH values of 5.0 and 7.0. High-valent metal-oxo species such as Fe(IV)O and Mn(IV)O and superoxide anion radicals were determined to be the reactive species and were responsible for the oxidation of SMX. These reactive species were selective; therefore, the overall removal performance of SMX was not obviously influenced by high levels of water components including chloride ions, bicarbonates, and natural organic matters. The results from this study may promote the design and application of selective oxidation technologies for micropollutant abatement.

Cs3Bi2Br9/BiOBr S-scheme heterojunction for selective oxidation of benzylic C[sbnd]H bonds

Converting hydrocarbons into aldehydes in a green and environmentally benign way is of great significance in fine chemistry. In this work, all-inorganic Cs3Bi2Br9 perovskite nanoparticles were uniformly loaded on BiOBr nanosheets via an in-situ growth method, which can selectivity photoactivate aromatic C(sp3)H bond of toluene to generate benzaldehyde. According to the in-situ X-ray photoelectron spectroscopy characterization, the photogenerated electrons of BiOBr transfer to Cs3Bi2Br9 enforced by the internal electric field under light irradiation, resulting in S-scheme heterojunction. Furthermore, theoretical calculations indicate that toluene molecules are inclined to adsorb on the BiOBr surface, subsequently involving the oxidation reaction to generate benzyl radical (PhCH2•) by using the energetic holes of BiOBr, while the remaining photoinduced electrons in the conduction band (CB) of Cs3Bi2Br9 with powerful reduction ability reduce O2 into •O2−, which is the vital oxidative active species working on toluene selective oxidation process. Such an unexceptionable charge carrier utilization mode and tendentious adsorption behavior of reactants contribute to the optimized Cs3Bi2Br9/BiOBr heterojunction with excellent photocatalytic performance, achieving a maximum of 22.5% toluene conversion and 96.2% selectivity towards benzaldehyde formation. This work provides a rational photocatalyst heterojunction construction protocol for the selective oxidation of saturated aromatic CH bonds.