Catalytic Oxidation Reactions Research Articles

The Promoting Effect of Metal Vacancy on CoAl Hydrotalcite-Derived Oxides for the Catalytic Oxidation of Formaldehyde

Formaldehyde (HCHO) is a major harmful volatile organic compound (VOC) that is particularly detrimental to human health indoors. Therefore, effectively eliminating formaldehyde is of paramount importance to ensure indoor air quality. In this study, CoAl hydrotalcite (LDH) was prepared using the co-precipitation method and transformed into composite metal oxides (LDO) through calcination. Additionally, a metal Al vacancy was constructed on the surface of the composite metal oxides (EX-LDO and EX-LDO/NF) using an alkaline etching technique. SEM demonstrated the successful loading of CoAl-LDO onto nickel foam surfaces (LDO/NF), and an extended etching time resulted in a greater number of porous structures in the samples. XRD confirmed the successful synthesis of the precursor materials, CoAl hydrotalcite (CoAl-LDH) and CoAl layered double oxides (CoAl-LDO). EDS analysis confirmed a reduction in aluminum content after alkaline etching. XPS analysis verified the presence of abundant Co2+ and surface oxygen as crucial factors contributing to the catalyst’s excellent catalytic activity. The experimental results indicated that catalysts containing metal cation vacancies exhibited superior catalytic performance in formaldehyde oxidation compared to conventional hydrotalcite-derived composite oxides. H2-TPR confirmed a significant enhancement in the participation of lattice oxygen in the catalytic oxidation reaction; it was found that the proportion of surface lattice oxygen consumption by the E5-LDO catalyst (30.2%) is higher than that of the LDO catalyst (23.4%), and the proportion of surface lattice oxygen consumption by the E1-LDO/NF catalyst (27.5%) is higher than that of the LDO/NF catalyst (14.6%), suggesting that cation vacancies can activate the surface lattice oxygen of the material, thereby facilitating improved catalytic activity. This study not only reveals the critical role of surface lattice oxygen in catalytic oxidation activity, but also aids in the further development of novel catalysts for efficient room-temperature oxidation of HCHO. Moreover, it provides possibilities for developing high-performance catalysts through surface modification.

Carbon-supported VPO catalysts with fibrous structure: A new family of catalysts for partial oxidation reactions

The present contribution describes the synthesis of a carbon supported VPO catalyst with a fibrous structure. The synthesis method is simple, low-cost, scalable and reproducible that allows the formation of the bulk mixed oxide (VO)2P2O7 (VPP) active phase on the carbon support material. The preparation does not require any special reducing thermal treatments due to the ability of the carbon support to stabilize the VPP active phase since this carbon-based support is stable under oxidizing conditions up to around 400ºC allowing it to be used as for catalytic oxidation reactions. The stability of the carbon-supported VPP catalyst under reaction conditions was examined with in situ Raman under oxidizing/ H2 reducing cycles and n-butane oxidation conditions under both wet and dry conditions. These studies confirm the dynamic character of VPO phases, which interconvert under different conditions, and the stability of carbon-supported VPP phase under different environments. The novel carbon-supported catalyst exhibits an activity behavior like that observed for commercial catalysts that suggests a very promising catalytic material.

Kinetic and mechanistic aspects of cerium(iv) as an oxidant in ruthenium catalysed oxidation reaction: A mini review

Kinetic and mechanistic aspects of cerium(iv) as an oxidant in ruthenium catalysed oxidation reaction: A mini review

Study on Preparation of Ce/Cu‐BTC and Its Catalytic Oxidation Process of P‐Diethyl benzene to P‐Ethyl acetophenone in the Fixed‐Bed Reactor

AbstractA new cerium doped copper hybrid bimetallic organic framework (Ce/Cu‐BTC) was synthesized for oxidizing p‐diethylbenzene (PDEB) to p‐ethylacetophenone (EAP) in the batch and fixed‐bed reactors. The oxidization mechanism for PDEB to EAP over Ce/Cu‐BTC was investigated. Results show Ce/Cu‐BTC is a mischcrystal mixture of Ce‐BTC and Cu‐BTC, the addition of Ce can increase the crystal phase defects and enlarge the pore size of Cu‐BTC. The conversion rate of PDEB is above 95 % and the yield of EAP are stable at 75 % in the Ce/Cu‐BTC fixed bed reactor. A mixture of EAP, 1‐(4‐ethylphenyl)‐1‐ethanol (EPEA) and p‐diacetylbenzene (PDAB) can be detected in the outlet of the reactor. The PDEB with Ce4+/Cu2+, H2O2 and bromine free radical generate EPEA and EAP, the EAP is then further oxidized to PDAB. The mischcrystal structure of Ce/Cu‐BTC is beneficial to improve the catalytic oxidation activity and reaction rate of PDEB to EAP.

Homoleptic Fe(III) and Fe(IV) Complexes of a Dianionic C3-Symmetric Scorpionate.

High-valent iron species have been implicated as key intermediates in catalytic oxidation reactions, both in biological and synthetic systems. Many heteroleptic Fe(IV) complexes have now been prepared and characterized, especially using strongly π-donating oxo, imido, or nitrido ligands. On the other hand, homoleptic examples are scarce. Herein, we investigate the redox chemistry of iron complexes of the dianonic tris-skatylmethylphosphonium (TSMP2-) scorpionate ligand. One-electron oxidation of the tetrahedral, bis-ligated [(TSMP)2FeII]2- leads to the octahedral [(TSMP)2FeIII]-. The latter undergoes thermal spin-cross-over both in the solid state and solution, which we characterize using superconducting quantum inference device (SQUID), Evans method, and paramagnetic nuclear magnetic resonance spectroscopy. Furthermore, [(TSMP)2FeIII]- can be reversibly oxidized to the stable high-valent [(TSMP)2FeIV]0 complex. We use a variety of electrochemical, spectroscopic, and computational techniques as well as SQUID magnetometry to establish a triplet (S = 1) ground state with a metal-centered oxidation and little spin delocalization on the ligand. The complex also has a fairly isotropic g-tensor (giso = 1.97) combined with a positive zero-field splitting (ZFS) parameter D (+19.1 cm-1) and very low rhombicity, in agreement with quantum chemical calculations. This thorough spectroscopic characterization contributes to a general understanding of octahedral Fe(IV) complexes.

A disordered oxide as an active phase during CO catalytic oxidation on Ru(0001)

The identification of the active phase of a catalyst under operando conditions is probably the most relevant task in basic catalysis research. In this respect, the Ru(0001) surface during CO oxidation is a traditional studied model, for both its importance in applied catalysis and for its peculiar behavior. In this work, we study the CO catalytic oxidation reaction on flat and defective Ru(0001) surfaces, concluding that the highest activity is achieved in oxidizing conditions when a disordered and thin Ru oxide is formed at the surface. Also, we find that in defective surfaces, with a high density of surface steps, this reaction is enhanced, related to the facile sub-surface incorporation of atomic oxygen and to the easier formation of the oxide. Thus, the CO catalytic oxidation on Ru(0001) is a structure-sensitive reaction, being active on the surface of the oxide formed in reaction conditions.

Mechanistic Understanding of the Use of Single-Atom and Nanocluster Catalysts for Syngas Production via Partial Oxidation of Methane

Single-atom and nanocluster catalysts presenting potent catalytic activity and excellent stability are used in high-temperature applications such as in structural composites, electrical devices, and catalytic chemical reactions. Recently, more attention has been drawn to application of these materials in clean fuel processing based on oxidation in terms of recovery and purification. The most popular media for catalytic oxidation reactions include gas phases, pure organic liquid phases, and aqueous solutions. It has been proven from the literature that catalysts are frequently selected as the finest in regulating organic wastewater, solar energy utilization, and environmental treatment applications in most catalytic oxidation of methane vis-à-vis photons and in environmental treatment applications. Single-atom and nanocluster catalysts have been engineered and applied in catalytic oxidations considering metal–support interactions and mechanisms facilitating catalytic deactivation. In this review, the present improvements on engineering single-atom and nano-catalysts are discussed. In detail, we summarize structure modification strategies, catalytic mechanisms, methods of synthesis, and application of single-atom and nano-catalysts for partial oxidation of methane (POM). We also present the catalytic performance of various atoms in the POM reaction. Full knowledge of the use of remarkable POM vis-à-vis the excellent structure is revealed. Based on the review conducted on single-atom and nanoclustered catalysts, we conclude their viability for POM reactions; however, the catalyst design must be carefully considered not only for isolating the individual influences from the active metal and support but also for incorporating the interactions of these components.

Cu2+-regulated one-pot wet-chemical synthesis of uniform PdCu nanostars for electrocatalytic oxidation of ethylene glycol and glycerol

The fabrication of effective and stable electrocatalysts is crucial for practical applications of direct alcohol fuel cells (DAFCs). In this study, bimetallic PdCu nanostars (PdCu NSs) were fabricated by a Cu2+-modulated one-pot wet-chemical method, where cetyltrimethyl ammonium bromide (CTAB) worked as a structure-regulating reagent. The morphology, compositions, crystal structures and formation mechanism of the as-prepared PdCu NSs were investigated by a series of techniques. The unique architectures created abundant active sites, which resulted in a large electrochemical active surface area (9.5 m2 g−1). The PdCu NSs showed negative shifts in the onset potentials and large forward peak current densities by contrast with those of commercial Pd black for the catalytic ethylene glycol oxidation reaction (EGOR) and glycerol oxidation reaction (GOR). It revealed that the PdCu NSs outperformed Pd black in the similar surroundings. This work provides a constructive strategy for fabrication of high-efficiency electrocatalysts for alcohol fuel cells.

Enhanced Catalytic Performance of La-Doped CoMn2O4 Catalysts by Regulating Oxygen Species Activity for VOCs Oxidation

Tuning the oxygen species activity of transition metal oxide catalysts is essential for harnessing environmental catalytic oxidation reactions, and the mobility of lattice oxygen and activation ability of gas oxygen over CoMn2O4 were well modulated by in situ solvothermal-induced lanthanum doping for VOCs oxidation. Lanthanum species were successfully doped into the spinel lattice, and the toluene oxidation rate of Co1Mn1.9La0.1 increased by 20.74 times compared with that of the undoped Co1Mn2 catalyst at 220 °C. With lanthanum doping, the content of oxygen vacancies was remarkably increased (1.4-fold) due to oxygen atoms in unusual bonding situations. Higher mobility and reactivity of lattice oxygen species were achieved by weakening the metal–oxygen bond strength, favoring the conversion of toluene to CO2 and H2O. Furthermore, doping lanthanum into the spinel lattice also promoted the activation and replenishment of gas oxygen. Moreover, the oxidation of anhydride species, as a rate-determining step, could be significantly accelerated due to lanthanum doping. This work provided a credible comprehension of the regulation of spinel oxygen species by lanthanum doping in VOCs abatement to improve the atmospheric environment.

Multi-compartmental MOF microreactors derived from Pickering double emulsions for chemo-enzymatic cascade catalysis

Bioinspired multi-compartment architectures are desired in synthetic biology and metabolic engineering, as credited by their cell-like structures and intrinsic ability of assembling catalytic species for spatiotemporal control over cascade reactions like in living systems. Herein, we describe a general Pickering double emulsion-directed interfacial synthesis method for the fabrication of multicompartmental MOF microreactors. This approach employs multiple liquid–liquid interfaces as a controllable platform for the self-completing growth of dense MOF layers, enabling the microreactor with tailor-made inner architectures and selective permeability. Importantly, simultaneous encapsulation of incompatible functionalities, including hydrophilic enzyme and hydrophobic molecular catalyst, can be realized in a single MOF microreactor for operating chemo-enzymatic cascade reactions. As exemplified by the Grubb’ catalyst/CALB lipase driven olefin metathesis/ transesterification cascade reaction and glucose oxidase (GOx)/Fe-porphyrin catalyzed oxidation reaction, the multicompartmental microreactor exhibits 2.24–5.81 folds enhancement in cascade reaction efficiency in comparison to the homogeneous counterparts or physical mixture of individual analogues, due to the restrained mutual inactivation and substrate channelling effects. Our study prompts further design of multicompartment systems and the development of artificial cells capable of complex cellular transformations.

Ps−Pt nanozyme-based synergistic signal amplification biosensor for highly sensitive colorimetric detection of protein

Immunosorbent assay is one of the most popular immunological screening techniques which has been widely used for the clinical diagnosis of alpha-fetoprotein (AFP). While traditional immunosorbent assay (ELISA) suffers from low detection sensitivity due to its low intensity of colorimetric signal. To improve the sensitivity of AFP detection, we developed a new and sensitive immunocolorimetric biosensor by combining Ps-Pt nanozyme with terminal deoxynucleotidyl transferase (TdT)-mediated polymerization reaction. The determination of AFP was achieved by measuring the visual color intensity produced by the catalytic oxidation reaction of the 3,3′,5,5′-tetramethylbenzidine (TMB) solution with Ps-Pt and horseradish peroxidase (HRP). Owing to the synergistic catalysis of Ps-Pt and horseradish peroxidase HRP enriched in polymerized amplification products, this biosensor exhibited a significant color change within 25 s in the presence of 10–500 pg/mL AFP. This proposed method allowed for the specific detection of AFP with a detection limit of 4.30 pg/mL and even 10 pg/mL target protein could be distinguished clearly by visual observation. Furthermore, this biosensor could be applied to analysis of AFP in the complex sample and could be easily extended to the detection of other proteins.

Novel insight into the effect of relative humidity on the acetone photocatalytic decomposition using Ag−CeO2 under vacuum ultraviolet illumination: Catalytic synergies, performance, and mechanistic interpretation

The present work reports on the impact of relative humidity (RH) on the process of acetone oxidation in the absence and presence of Ag − CeO2 photocatalysts, including 185 nm vacuum UV (VUV) photolysis, ozonation, ozonation + 254 nm UV photolysis, and 254 nm UV photolysis treatment processes. The photocatalysts were evaluated by Raman, SEM, XRD, HRTEM, EPR, EDS, and XPS techniques. The information from characterization tests revealed that modification of ceria structure by the introduction of Ag nanoparticles increases the photocatalyst oxygen storage ability, which promotes the oxygen vacancies formation, resulting in the lattice oxygen activation. The attained data demonstrated the dual role of RH in the process of acetone oxidation under VUV irradiation. Compared to the dry condition, the introduction of RH = 25, 45, and 65% to the VUV photolysis system enhances the conversion of acetone remarkably from 40% to 60, 68, and 72%, respectively. However, the acetone oxidation did not change significantly in the presence of RH = 25–65% over the Ag − CeO2/VUV system. This observation confirms the dual role of RH; while RH boosted the gas phase photooxidation reactions, it poisoned the gas–solid interface, leading to an inhibitory effect on the catalytic oxidation reactions. Moreover, the results showed that the lower level of relative humidity (e.g., RH = 5%) over the Ag − CeO2 under VUV light not only enhances the acetone oxidation to 88% but also, through the participation of the catalytic ozonation, decomposed the formed O3 and increased the selectivity of the reaction towards complete oxidation up to 97%. The acetone oxidation mechanism was studied where the EPR results show that both.OH and.O2– contribute to acetone oxidation. Finally, the Ag − CeO2/VUV reusability was assessed in a way that the in-situ procedure for photocatalyst regeneration was utilized to inhibit the catalyst deactivation.

Highly Selective Activation of C–H Bond and Inhibition of C–C Bond Cleavage by Tuning Strong Oxidative Pd Sites

Improving the product selectivity meanwhile restraining deep oxidation still remains a great challenge over the supported Pd-based catalysts. Herein, we demonstrate a universal strategy where the surface strong oxidative Pd sites are partially covered by the transition metal (e. g., Cu, Co, Ni, and Mn) oxide through thermal treatment of alloys. It could effectively inhibit the deep oxidation of isopropanol and achieve the ultrahigh selectivity (>98%) to the target product acetone in a wide temperature range of 50-200 °C, even at 150-200 °C with almost 100% isopropanol conversion over PdCu1.2/Al2O3, while an obvious decline in acetone selectivity is observed from 150 °C over Pd/Al2O3. Furthermore, it greatly improves the low-temperature catalytic activity (acetone formation rate at 110 °C over PdCu1.2/Al2O3, 34.1 times higher than that over Pd/Al2O3). The decrease of surface Pd site exposure weakens the cleavage for the C-C bond, while the introduction of proper CuO shifts the d-band center (εd) of Pd upward and strengthens the adsorption and activation of reactants, providing more reactive oxygen species, especially the key super oxygen species (O2-) for selective oxidation, and significantly reducing the barrier of O-H and β-C-H bond scission. The molecular-level understanding of the C-H and C-C bond scission mechanism will guide the regulation of strong oxidative noble metal sites with relatively inert metal oxide for the other selective catalytic oxidation reactions.

Leveraging a Structural Blueprint to Rationally Engineer the Rieske Oxygenase TsaM.

Rieske nonheme iron oxygenases use two metallocenters, a Rieske-type [2Fe-2S] cluster and a mononuclear iron center, to catalyze oxidation reactions on a broad range of substrates. These enzymes are widely used by microorganisms to degrade environmental pollutants and to build complexity in a myriad of biosynthetic pathways that are industrially interesting. However, despite the value of this chemistry, there is a dearth of understanding regarding the structure-function relationships in this enzyme class, which limits our ability to rationally redesign, optimize, and ultimately exploit the chemistry of these enzymes. Therefore, in this work, by leveraging a combination of available structural information and state-of-the-art protein modeling tools, we show that three "hotspot" regions can be targeted to alter the site selectivity, substrate preference, and substrate scope of the Rieske oxygenase p-toluenesulfonate methyl monooxygenase (TsaM). Through mutation of six to 10 residues distributed between three protein regions, TsaM was engineered to behave as either vanillate monooxygenase (VanA) or dicamba monooxygenase (DdmC). This engineering feat means that TsaM was rationally engineered to catalyze an oxidation reaction at the meta and ortho positions of an aromatic substrate, rather than its favored native para position, and that TsaM was redesigned to perform chemistry on dicamba, a substrate that is not natively accepted by the enzyme. This work thus contributes to unlocking our understanding of structure-function relationships in the Rieske oxygenase enzyme class and expands foundational principles for future engineering of these metalloenzymes.

From waste to wealth: a cellulose-based fibrous membrane from recycled cigarettes supported with dual perovskite for formaldehyde degradation at room temperature

Formaldehyde, as a hazardous indoor contaminant following house decoration, is essential to its efficient removal at room temperature. This paper reports an eco-friendly approach for extracting cellulose acetate (CA) from waste cigarette filters to construct a nanofibrous composite membrane for formaldehyde degradation at ambient temperature. A composite nanofibrous membrane was fabricated by salable electrospinning of cellulose acetate and La2CoMnO6/CeO2 (LC), followed by hydrolysis and potassium doping with KOH. The membrane demonstrates excellent catalytic activity (97.56% of conversion), super stability (95.35% of conversion after 50 h) and long service life (93.96% of conversion after 3 catalysis cycles), which is ascribed to the synergistic catalytic effect of double perovskite and rapid hygroscopic properties of cellulose. In addition, the obtained membrane has a higher moisture regain (7.82%) than that of the LC/CA nanofibrous membrane (2.21%), and higher than that of the commercial air filter membrane using polypropylene (PP) fiber (near zero), accelerating formaldehyde adsorption and fastening the water removal, thereby allowing for the long-term positive progress of formaldehyde catalytic oxidation reaction. This work provides encouraging guidance for further exploration into formaldehyde degradation, which is promising for application in air cleaning.

Pickering emulsion enhanced interfacial catalysis under Taylor flow in a microchannel reactor

There are still technical challenges associated with surface fouling and clogging in microchannels when conducting multiphase catalytic reactions involving solid particles. In this study, a Pickering emulsion was employed to enhance the oxidation of benzyl alcohol (BNOH) catalyzed by Pd/SiO2 nanoparticles under Taylor flow in a microchannel reactor. The reaction characteristics of benzyl alcohol/water Pickering emulsion in a microchannel reactor were studied experimentally. The characteristic results showed that the O/W Picking emulsion system was superior to the W/O Picking emulsion system for the catalytic oxidation reaction. The influences of a wide range of operational variables were characterized on the conversion of reactants and the selectivity of the desired product. The optimized reaction conditions included: reaction temperature 403 K, CB 5 wt%, O2/BNOH (mol/mol) 0.76 and tube length 8 m. Under the optimal operating conditions, the conversion of BNOH and the selectivity of benzaldehyde were found to be 86.53% and 99.79%, respectively. In addition, the interfacial transport-reaction mechanism in Pickering emulsions under Taylor flow in microchannels was proposed from the perspective of multiphase mass transfer. This development provided significant insights and guiding for effectively performing multiphase catalytic reactions involving solid catalyst particles in microchannel reactors.

Kinetics of Catalytic Oxidation of Oleic Acid Methyl Ester

The results of studying the kinetics of the reaction of catalytic oxidation of oleic acid methyl ester with hydrogen peroxide in a two-phase system (aqueous phase-organic phase) in the presence of a bifunctional catalyst of the composition [(Octn)3NMe]3{PO4[WO(O2)2]4} are presented. For the selected reaction conditions, the first orders of catalyst, substrate and oxidizer are established. The value of the activation energy for the temperature range 313–353 K is 47 ± 3 kJ/mol, and the pre-exponential multiplier is (6.0 ± 0.3) × 107 L2 mol–2 min–1.

Synthesis of Ni-Co alloy nanocrystalline powder by a novel chemical method and their characterization

The bimetallic or trimetallic alloy nanoparticles (NPs) are sought after in different applications due to their enhanced activity caused by the synergistic characteristics and increased surface area inherent to nano particles. The Ni-Co nanoparticles (NPs) have wide applications in biomedical field, magnetic storage media, ferrofluids, hydrogen storage, generation of hydrogen and catalytic oxidation reactions due to their good chemical stability and high magnetic anisotropy. Ultrafine particles of Ni-Co alloy were synthesized by a novel chemical method in aqueous medium using aluminum as a reducing agent. The uniqueness of this approach is that there is no need of any extra inert atmosphere to conduct the NPs synthesis. The Ni-Co alloy particles were obtained by co-reducing the nickel and cobalt metal precursors in the desired molar ratios with fixed quantity of aluminum powder. The Ni-Co NPs synthesized were having grain size less than 20 nm. The effect of cobalt content on the structure and magnetic properties of Ni-Co alloys were studied. It was observed that the formation of Ni-Co NPs alloy proceeded upto 70 % of Co. Compositional analysis showed that the precursor ratio was almost preserved in the Ni-Co alloy powders. X-ray diffraction indicated FCC structure for Ni-Co solid solution. The annealing of the synthesized Ni-Co NPs at 400 ˚C in furnace for an hour (in nitrogen atmosphere) indicated forming of well defined FCC crystalline peaks. Saturation magnetization increased as a function of Co content in Ni-Co alloy and the alloy with high Co content saturates only at a high field.

2‐Hydroxyadipic Acid Production by Oxidation of 2‐Hydroxycyclohexanone with Molecular Oxygen

AbstractOxidation of 2‐hydroxycyclohexanone (2‐HCO) which can be synthesized from both petroleum and biomass was investigated with heteropolyacids and oxygen as catalysts and oxidant, respectively. 2‐Hydroxyadipic acid (2‐HAA) was obtained in moderate yields, and H4PVW11O40 gave the highest yield (39 %). 2‐HAA is a dicarboxylic acid expected to be a monomer, and this work is the first report for production of 2‐HAA by catalytic oxidation reactions. The oxidation of 1,2‐cyclohexanedione (CHDO), which is a potential intermediate of 2‐HCO oxidation, produced similar yield of 2‐HAA even without catalyst. The effects of catalyst amount (first order), oxygen pressure (almost zero order) and the addition of radical scavenger (no effect) on the 2‐HCO oxidation with H4PVW11O40 catalyst were similar to those in a related case of 2‐methoxycyclohexanone oxidation to adipic acid with heteropolyacid catalyst. 2‐HCO is proposed to be oxidized to CHDO as a precursor of 2‐HAA in a similar mechanism to 2‐methoxycyclohexanone oxidation.

Engineering Active Surface Oxygen Sites of Cubic Perovskite Cobalt Oxides toward Catalytic Oxidation Reactions

Engineering Active Surface Oxygen Sites of Cubic Perovskite Cobalt Oxides toward Catalytic Oxidation Reactions