Catalysts For Selective Oxidation Research Articles

Biotemplated heterostructure materials: opportunities for the elaboration of new photocatalysts and selective-oxidation catalysts

Natural biological materials display a large number of sophisticated nanostructures that are difficult to acquire even using the most technologically advanced synthetic methodologies.

Significant inhibition of secondary pollution in the catalytic oxidation of chloroaromatics over a bifunctional Ru1/CeO2 single-atom catalyst

Single atomic Ru supported CeO2 seems to be a more promising and selective catalyst for chlorobenzene oxidation than RuO2 NPs, which enables the inhibition of HCl conversion to Cl2 and stepwise formation of polychlorinated by-products.

Facile hydrothermal synthesis of VO2 nanosheets as robust catalysts for liquid-phase selective oxidation of benzyl alcohol under atmospheric O2

The liquid-phase selective oxidation of benzyl alcohol is a sustainable route for the synthesis of benzaldehyde. Wherein, the exploration of heterogeneous and cheap metal oxide catalysts instead of noble metal...

Cobalt phthalocyanine (CoPc) anchored on Ti3C2 MXene nanosheets for highly efficient selective catalytic oxidation.

Quinclorac is an important precursor for pharmaceutical, agricultural, and synthetic chemistry. The state-of-the-art synthesis of quinclorac via condensation, chlorination and oxidative hydrolysis often uses homogeneous catalysts and strong acid oxidant agents to promote the catalytic oxidation, which requires huge manpower input for the late-stage purification process and is usually environmentally unfriendly. In this work, we successfully fabricated a stable cobalt phthalocyanine (CoPc) Co-based composite (CoPc/Ti3C2) by anchoring CoPc on the surface of Ti3C2 nanosheets for the selective oxidation of 3,7-dichloro-8-dichloro methyl quinoline (3,7-D-8-DMQ) into quinclorac. More impressively, CoPc/Ti3C2-4.5%-Mn-Br exhibits a high selectivity of 91.8% for the catalytic oxidation of 3,7-D-8-DMQ to quinclorac in acetic acid, with a quinclorac yield of 87.5%, which is approximately 2.46 times higher than that of pristine CoPc-Mn-Br. The obtained heterogeneous catalytic system shows good reusability. Detailed mechanistic investigations reveal that the system works through the free radical mechanism via the formation of Co2+/Co3+ redox cycles. This work provides a new understanding for the stabilization of reaction intermediates and facilitates the design of catalysts for selective catalytic oxidation.

Ru nanoclusters supported on a bimodal N,S-doped mesoporous carbon: an efficient and reusable catalyst for selective aerobic oxidation of alcohols and amines

Ru nanoparticles supported on a bimodal N, S-doped mesoporous carbon catalyzing the oxidation of various alcohols and amines, giving the respective aldehydes/ketones and nitriles/imines in high yields and selectivity.

Mesoporous ceria-supported vanadia catalysts for selective aerobic oxidation of ethylbenzene

A series of mesoporous ceria-supported vanadium oxide catalysts were prepared and explored for aerobic oxidation of ethylbenzene to acetophenone without the involvement of any solvent or additive.

Synthesis and catalytic application of nanostructured metal oxides and phosphates.

The design and development of new high-performance catalysts is one of the most important and challenging issues to achieve sustainable chemical and energy production. This Feature Article describes the synthesis of nanostructured metal oxides and phosphates mainly based on earth-abundant metals and their thermocatalytic application to selective oxidation and acid-base reactions. A simple and versatile methodology for the control of nanostructures based on crystalline complex oxides and phosphates with diverse structures and compositions is proposed as another approach to catalyst design. Herein, two unique and verstile methods for the synthesis of metal oxide and phosphate nanostructures are introduced; an amino acid-aided method for metal oxides and phosphates and a precursor crystallization method for porous manganese oxides. Nanomaterials based on perovskite oxides, manganese oxides, and metal phosphates can function as effective heterogeneous catalysts for selective aerobic oxidation, biomass conversion, direct methane conversion, one-pot synthesis, acid-base reactions, and water electrolysis. Furthermore, the structure-activity relationship is clarified based on experimental and computational approaches, and the influence of oxygen vacancy formation, concerted activation of molecules, and the redox/acid-base properties of the outermost surface are discussed. The proposed methodology for nanostructure control would be useful not only for the design and understanding of the complexity of metal oxide catalysts, but also for the development of innovative catalysts.

Design strategy for effective supported Au–Pd catalysts for selective oxidation of 5-hydroxymethylfurfural under mild conditions

The strategy to rationally design effective bimetallic AuPd/ZrO2 catalysts for the selective HMF oxidation under mild conditions is introduced.

Anderson-type polyoxometalate-based metal-organic framework as an efficient heterogeneous catalyst for selective oxidation of benzylic C-H bonds.

Oxidative transformation of benzylic C-H bonds into functional carbonyl groups under mild conditions represents an efficient method for the synthesis of aromatic carboxylic acids and ketones. Here we report a high-efficiency catalyst system constructed from an Anderson-type polyoxometalate-based metal-Organic framework (POMOF-1) and N-hydroxyphthalimide (NHPI) for selective oxidation of methylarenes and alkylarenes under 1 atm O2 atmosphere. POMOF-1 exerted a synergistic effect originating from the well-aligned Anderson {CrMo6} clusters and Cu centers within the framework, and this entailed good cooperation with NHPI to catalyze the selective oxidation. Accordingly, the reactions exhibit good tolerance and chemical selectivity for a wide range of substrates bearing diverse substituent groups, and the corresponding carboxylic acids and ketones were harvested in good yields under mild conditions. Mechanism study reveals that POMOF-1 worked synergistically with NPHI to activate the benzylic C-H bonds of substrates, which are sequentially oxidized by oxygen and HOO˙ to give rise to the products. This work may pave a way to design high-efficiency catalysts by integration of polyoxometalate-based materials with NPHI for challenging C-H activation.

Bifunctional 3D POM-based coordination polymers for improved pseudocapacitance and catalytic oxidation performance.

Developing novel high-efficiency supercapacitors as energy storage devices to solve the energy crisis is of vital significance. Meanwhile, designing highly active and selective oxidation catalysts for various sulfides is desirable but still a big challenge. To work out these problems, three novel 3D POM-based coordination polymers (POMCPs), formulated as [{Ag6(pytz)4}{SiMo12O40}] (1), [{Cu3(pytz)4}{SiMo12O40}]·5.5H2O (2) and [{Cu6(pytz)6}{SiMo12O40}]·2H2O (3) (pytz = 4-(5-(4-pyridyl)-1H-tetrazole)), are successfully prepared via a one-step synthetic strategy by changing different temperatures under hydrothermal or solvothermal conditions. In compounds 1 and 2, {SiMo12}, as 9-capped and 2-capped polyoxoanions, are engaged among the 2D Ag/Cu-organic sheets to generate the novel 3D POM-based coordination polymers. In addition, 1D Cu-organic chains are combined with 3-capped {SiMo12} polyoxoanions to construct 2D POM-based coordination polymers in 3. To our delight, as electrode materials for supercapacitors, the three compounds exhibit excellent specific capacitances of 261.76 F g-1, 248.82 F g-1 and 156.47 F g-1 at 0.5 A g-1, respectively. Besides, they can effectively and selectively catalyze the oxidation of various sulfides to sulfoxides.

Catalytic Activity of Nonaggregating Cu Nanoparticles Supported in Pores of Zeolite for Aerobic Oxidation of Benzyl Alcohol.

Cu nanoparticles (NPs) as catalysts have the good advantage of being more abundant than noble metal NPs. In this study, we synthesized nonaggregating Cu NPs supported in Y-type zeolite by the photoreduction method. In this method, Cu ions in pores of zeolite can be slowly reduced with a small amount of reductant at room temperature. The high-resolution transmission electron microscope, energy dispersive X-ray spectroscopy, X-ray diffraction patterns, and UV-Vis spectra supported that nonaggregating Cu NPs existed in the pores of zeolite. Catalytic activities of Cu NP-zeolite were investigated for the aerobic oxidation of benzyl alcohol. Our Cu NP-zeolite had a large turnover frequency of 17 h-1. The yield of benzaldehyde increased in proportion to the amount of Cu loading at ≤0.5 wt %, indicating that Cu NPs in pores of zeolite work as catalysts for selective aerobic oxidation of benzyl alcohol. The high catalytic activity was brought by nonaggregating Cu NPs in pores of zeolite. The catalytic reaction for other aromatic alcohols with electron-donating groups proceeded, whereas it did not proceed for the aromatic alcohols with electron-withdrawing groups or aliphatic alcohols, indicating that the interaction between zeolite and the benzene ring also contributed to the reaction. This study would be expected to contribute to the development of Cu NP catalysts.

Cobalt Encapsulated in Nitrogen-Doped Graphite-like Shells as Efficient Catalyst for Selective Oxidation of Arylalkanes.

Selective oxidation of ethylbenzene to acetophenne is an important process in both organic synthesis and fine chemicals diligence. The cobalt-based catalysts combined with nitrogen-doped carbon have received great attention in ethylbenzene (EB) oxidation. Here, a series of cobalt catalysts with metallic cobalt nanoparticles (NPs) encapsulated in nitrogen-doped graphite-like carbon shells (Co@NC) have been constructed through the one-pot pyrolysis method in the presence of different nitrogen-containing compounds (urea, dicyandiamide and melamine), and their catalytic performance in solvent-free oxidation of EB with tert-butyl hydrogen peroxide (TBHP) as an oxidant was investigated. Under optimized conditions, the UCo@NC (urea as nitrogen source) could afford 95.2% conversion of EB and 96.0% selectivity to acetophenone, and the substrate scalability was remarkable. Kinetics show that UCo@NC contributes to EB oxidation with an apparent activation energy of 32.3 kJ/mol. The synergistic effect between metallic cobalt NPs and nitrogen-doped graphite-like carbon layers was obviously observed and, especially, the graphitic N species plays a key role during the oxidation reaction. The structure-performance relationship illustrated that EB oxidation was a free radical reaction through 1-phenylethanol as an intermediate, and the possible reaction mechanistic has been proposed.

Transition-Metal-Promoted Cu-SSZ-13 Catalysts for Continuous Selective Oxidation of Methane to Methanol Using Molecular Oxygen

Transition-Metal-Promoted Cu-SSZ-13 Catalysts for Continuous Selective Oxidation of Methane to Methanol Using Molecular Oxygen

A novel bifunctional Pt/Ce/WZrOx catalyst for efficient selective oxidation of high-concentration NH3

A novel bifunctional catalyst with excellent NH3-SCO and NH3-SCR functions is effective to achieve excellent low-temperature activity and high N2 selectivity simultaneously, especially for removing high-concentration NH3 slipped from NH3-fuel engine exhaust gas. Herein, a small amount of noble metal Pt (0.1 wt%) was introduced in Ce/WZrOx to synthesize a novel bifunctional NH3-SCO catalyst. The experimental results showed that deposition order of Pt and Ce active species supported on WZrOx had a significant influence on NH3-SCO performance. Pt/Ce/WZrOx catalyst prepared through impregnation-precipitation method exhibited a much superior comprehensive NH3 removal performance compared to Pt/Al2O3 catalyst (Pt 0.1 wt%). It achieved an NH3 conversion of 96.4 % and a N2 selectivity of 94.2 % at 310 °C. A series of characterization tests were adopted to compare the physicochemical properties of Pt/Ce/WZrOx and Ce/WZrOx catalysts to reveal the possible functions of Pt and Ce active species in NH3-SCO reactions. The results of H2-TPR implied that there was a strong interaction between the Pt and Ce active species, which greatly enhanced the low-temperature redox property of Pt/Ce/WZrOx catalyst. Besides, electron transfer between Pt0/Ptn+ and Ce3+/Ce4+ cycles facilitated the generation of oxygen vacancies on the Pt/Ce/WZrOx catalyst surface, which played a key role in the reaction for removing high-concentration NH3. In-situ DRIFTS results suggested that NH3-SCO reactions over Pt/Ce/WZrOx catalyst might follow both imide (–NH) and hydrazine (-N2H4) mechanisms.

An efficient vanadium phosphorus oxide catalyst prepared by tuning vanadium precursor for selective oxidation of n-butane to maleic anhydride

Maleic anhydride (MA), as an industrially important chemical, is currently produced through selective oxidation of n-butane (SOB) over vanadium-phosphorus-oxygen (VPO) catalyst, but sufferring from low selectivity by overoxidation. Therefore, preparing selective VPO catalysts is urgent, but remains a challenge. Herein, we prepared an efficient VPO catalyst (VPO-Vsg) by using the pre-synthesized V2O5 (V2O5-sg) via a sol–gel process as V source. It shows about 90 % n-butane conversion with more than 70 % MA selectivity under 2000 h−1 and 400 °C conditions. It shows much superior MA yield (more than 60 %) to the VPO catalyst prepared by using commercially available V2O5 (V2O5-ca) as V source, ascribed to the optimal V oxidation state and lattice oxygen content, and the decreasing V5+ contributes its higher selectivity. This study not only generates an excellent VPO catalyst for MA production, but also provides a facile and effective approach for designing efficient catalysts for hydrocarbon selective oxidation.

Fe-Ni bimetallic supported on mordenite catalyst for selective oxidation of veratryl alcohol in a continuous reactor

Veratryl alcohol (VA) is preferentially oxidized to veratraldehyde (VADE) using a heterogeneous catalyst, which is more favoured in industries. Commercial mordenite (Ca,Na2,K2) Al2Si10O24·7H2O) was desilicated with NaOH and loaded with nickel and iron bimetal by the wet impregnation method. The synthesised Mordenite-Fe(5 %)/Ni(5–20 %) bimetallic catalyst, possessing active Bronsted acid sites, was employed to selectively oxidize the veratryl alcohol reaction. FT-IR, XRD, BET, HR-SEM, HR-TEM, and TPD were employed to determine the catalyst's textural attributes, morphology, chemical properties, and stability. Selective oxidation was performed over the catalysts using TBHP as an oxidant in a continuous reactor. To examine the most active catalyst among the four and to maximise the conversion and yield, the reaction conditions are optimised for various reaction parameters The reaction conditions were optimized by attaining 100 % conversion at temperature (90° C) for time (2 hr) and a maximum conversion of 97 % and a selectivity of 99 % at 10 bar pressure, WHSV (1.0 h−1) with acetonitrile solvent. The result of the study display that Fe (5 %) and Ni(15 %) impregnated on mordenite exhibits excellent catalytic stability with conversion (100 %) and selectivity (99 %) among the other catalysts. During regeneration, the conversion rate declined from 99.5 to 92.4.7 % and selectivity declined from 100 % to 96.2 % at the end of the seventh cycle. The high selectivity and stability of MOR-Fe(5 %)/Ni(15 %) imply that they might function properly as appropriate catalysts for the oxidation of aromatic alcohols. The advantages of the current synthesis are its cost-efficiency and eco-friendliness.

Lattice-Stabilized Chromium Atoms on Ceria for N2O Synthesis.

The development of selective catalysts for direct conversion of ammonia into nitrous oxide, N2O, will circumvent the conventional five-step manufacturing process and enable its wider utilization in oxidation catalysis. Deviating from commonly accepted catalyst design principles for this reaction, reliant on manganese oxide, we herein report an efficient system comprised of isolated chromium atoms (1 wt %) stabilized in the ceria lattice by coprecipitation. The latter, in contrast to a simple impregnation approach, ensures firm metal anchoring and results in stable and selective N2O production over 100 h on stream up to 79% N2O selectivity at full NH3 conversion. Raman, electron paramagnetic resonance, and in situ UV-vis spectroscopies reveal that chromium incorporation enhances the density of oxygen vacancies and the rate of their generation and healing. Accordingly, temporal analysis of products, kinetic studies, and atomistic simulations show lattice oxygen of ceria to directly participate in the reaction, establishing the cocatalytic role of the carrier. Coupled with the dynamic restructuring of chromium sites to stabilize intermediates of N2O formation, these factors enable catalytic performance on par with or exceeding benchmark systems. These findings demonstrate how nanoscale engineering can elevate a previously overlooked metal into a highly competitive catalyst for selective ammonia oxidation to N2O, paving the way toward industrial implementation.

Organic-inorganic hybridized Mo/Pd-based complexes as efficient catalysts for selective aerobic oxidation of benzyl alcohols

Organic-inorganic hybrid crystalline compounds have demonstrated outstanding potential utilization in a wide range of catalytic applications. Herein, three organic–inorganic hybrids Mo/Pd-based complexes Mo2O4(CF3COO)2(DMSO)4 (compound 1), Pd(C6H5CH2)2NCS2)2 (compound 2) and Pd[(CH3)2CHCH2NCS2]2 (compound 3) have been controllably synthesized and fully characterized. Remarkably, benefiting from coordinated solvent molecules, the dinuclear oxomolybdates 1 exhibits the efficient homogeneous catalytic activities for the selective aerobic oxidation of benzyl alcohols under ambient pressure (yields up to 90%). Moreover, compound 1 can be reused three cycles in the reactions without significant loss of activity and the possible catalytic mechanisms also be proposed.

Controllable creating mesoporous coordination unsaturated sites in UiO-66 single crystals for efficient conversion of hydrogen sulfide into polysulphur

We report herein a facile pyrolysis etching strategy for the fabrication of UiO-66-xs single crystals with tunable coordination unsaturated zirconium sites (Zr-CUS) as well as interconnected mesoporosity. The synthesis is realized by having pristine UiO-66-xs subjected to thermal treatment, which results in the selective decomposition of thermal-sensitive organic linkers and hence the creation of permanent mesoporosity, leaving abundant Zr-CUS with enhanced degree of exposure. The prepared hierarchically porous UiO-66-xs (HP-UiO-66-xs) were innovatively applied for mild oxidation of H2S into polysulphur, achieving near 100 % H2S conversion and polysulphur selectivity in a wide range of temperatures. The superior activities can be well maintained in a continuous test of over 50 h. The Zr-CUS of HP-UiO-66-xs effectively activate H2S and O2 via the “adsorption dissociation tandem hydrogen transfer” mechanism, and the abundant mesochannels ensure efficient transport of reactants and bulky products in and out HP-UiO-66-xs, leading to catalytic activities superior to those of traditional H2S selective oxidation catalysts.

SiO2 supported Co3O4 catalyst for selective oxidation of cyclohexene with molecular oxygen

SiO2 supported Co3O4 catalyst for selective oxidation of cyclohexene with molecular oxygen