Activity For Selective Oxidation Research Articles

Phenyl-doped porous carbon nitride for enhanced visible light-driven photocatalytic oxidation of aromatic alcohols

The g-C3N4 is one of the most promising photocatalytic materials in the recent decades，but its development is limited by its low carrier separation efficiency. The doping of g-C3N4 is a very effective way to regulate its photoelectric properties. Here, the phenyl was successfully doped into basic structural unit heptaazine ring of g-C3N4 by co-polymerization strategy. It was found that the presence of benzene ring increased the BET surface area (75.8 ​m2 ​g−1) of porous C3N4, enhanced the visible light absorption, narrowed the band gap and improved the photocarrier separation efficiency. The improvement of these properties enhances the photoelectric properties of pure g-C3N4.The phenyl-doped porous C3N4 exhibits excellent photocatalytic activity for selective oxidation of benzyl alcohol. When the addition mass of 2-aminbenzonitrile is 0.3 ​g, the conversion rate of benzyl alcohol reaches 94.5% under 8 ​h of solar radiation, which is about 2.1 times that of pure porous C3N4.

In Situ Observation of Hot Carrier Transfer at Plasmonic Au/Metal-Organic Frameworks (MOFs) Interfaces.

Constructing heterostructures have been demonstrated as an ideal strategy for boosting charge separation on plasmonic photocatalysts, but the detailed interface charge transfer mechanism remains elusive. Herein, that authors fabricate plasmonic Au and metal-organic frameworks (MOFs, NH2 -MIL-125 and MIL-125 used in this work) heterostructures and explore the interface charge transfer mechanism by in situ electron paramagnetic resonance (EPR) spectroscopy and electrochemical measurements. The plasmon-excited hot electrons on Au can transfer across the Au/MOF interface and be captured by the coordinatively unsaturated sites of secondary building units (Ti8 O8 (OH)4 cluster) of the MOF structure, and the plasmon-excited hot holes on Au tend to transfer to and be trapped at the functionalized organic ligand (1,4-benzenedicarboxylate-NH2 ). The spatially separated hot electrons and holes exhibit boosted the photocatalytic activity for chromium (VI) reduction and selective benzyl alcohol oxidation. This work illustrates the advantage of the versatile functionalization of MOF structures enabling molecular-level manipulation of interface charge transfer on plasmonic photocatalysts.

Controllable Assembly of Vanadium-Containing Polyoxoniobate-Based Materials and Their Electrocatalytic Activity for Selective Benzyl Alcohol Oxidation.

During the controllable synthesis of two vanadium-containing Keggin-type polyoxoniobates (PONbs), [Ni(en)2]5[PNb12O40(VO)5](OH)5·18H2O (1) and [Ni(en)3]5[PNb12O40(VO)2]∙17H2O (2, en = ethylenediamine) are realized by changing the vanadium source and hydrothermal temperature. Compounds 1 and 2 have been thoroughly characterized by single-crystal X-ray diffraction analysis, FT-IR spectra, X-ray photoelectron spectrum (XPS), powder X-ray diffraction (PXRD), etc. Compound 1 contains a penta-capped Keggin-type polyoxoniobate {PNb12O40(VO)5}, which is connected by adjacent [Ni(en)2]2+ units into a three-dimensional (3D) organic-inorganic framework, representing the first nickel complexes connected vanadoniobate-based 3D material. Compound 2 is a discrete di-capped Keggin-type polyoxoniobate {PNb12O40(VO)2} with [Ni(en)3]2+ units as counter cations. Compounds 1 and 2 have poor solubility in common solvents and can keep stable in the pH range of 4 to 14. Notably, both 1 and 2 as electrode materials are active for the selective oxidation of benzyl alcohol to benzaldehyde. Under ambient conditions without adding an alkaline additive, compound 1 as a noble metal free electrocatalyst can achieve 92% conversion of benzyl alcohol, giving a Faraday efficiency of 93%; comparatively, 2 converted 79% of the substrate with a Faraday efficiency of 84%. The control experiments indicate that both the alkaline polyoxoniobate cluster and the capped vanadium atoms play an important role during the electrocatalytic oxidation process.

Chemically Bonded α-Fe2 O3 /Bi4 MO8 Cl Dot-on-Plate Z-Scheme Junction with Strong Internal Electric Field for Selective Photo-oxidation of Aromatic Alcohols.

Inferior contact interface and low charge transfer efficiency seriously restrict the performance of heterojunctions. Herein, chemically bonded α-Fe2 O3 /Bi4 MO8 Cl (M=Nb, Ta) dot-on-plate Z-scheme junctions with strong internal electric field are crafted by an in situ growth route. Experimental and theoretical results demonstrate that the internal electric field provides a powerful driving force for vectorial migration of photocharges between Bi4 MO8 Cl and α-Fe2 O3 , and the interfacial Fe-O bond not only serves as an atomic-level charge flow highway but also lowers the charge transfer energy barrier, thereby accelerating Z-scheme charge transfer and realizing effective spatial charge separation. Impressively, α-Fe2 O3 /Bi4 MO8 Cl manifests a significantly improved photocatalytic activity for selective oxidation of aromatic alcohols into aldehydes (Con. ≥92 %, Sel. ≥96 %), with a performance improvement of one to two orders of magnitude. This work presents atomic-level insight into interfacial charge flow steering.

Chemically Bonded α‐Fe2O3/Bi4MO8Cl Dot‐on‐Plate Z‐Scheme Junction with Strong Internal Electric Field for Selective Photo‐oxidation of Aromatic Alcohols

AbstractInferior contact interface and low charge transfer efficiency seriously restrict the performance of heterojunctions. Herein, chemically bonded α‐Fe2O3/Bi4MO8Cl (M=Nb, Ta) dot‐on‐plate Z‐scheme junctions with strong internal electric field are crafted by an in situ growth route. Experimental and theoretical results demonstrate that the internal electric field provides a powerful driving force for vectorial migration of photocharges between Bi4MO8Cl and α‐Fe2O3, and the interfacial Fe−O bond not only serves as an atomic‐level charge flow highway but also lowers the charge transfer energy barrier, thereby accelerating Z‐scheme charge transfer and realizing effective spatial charge separation. Impressively, α‐Fe2O3/Bi4MO8Cl manifests a significantly improved photocatalytic activity for selective oxidation of aromatic alcohols into aldehydes (Con. ≥92 %, Sel. ≥96 %), with a performance improvement of one to two orders of magnitude. This work presents atomic‐level insight into interfacial charge flow steering.

Solvent-free aerobic selective oxidation of benzyl alcohol over La-Co bimetallic catalyst: A kinetic study

It is desirable but challenging to explore non-noble metal based catalyst for the solvent-free aerobic oxidation of benzyl alcohol to benzaldehyde. LayCo1Ox was prepared through a co-precipitation method, which exhibited excellent catalytic performance for titled reaction with a yield of 73.1% and selectivity of 99.6%. Introduction of La in the Co3O4 can modify the electronic property of Co, improving the surface Co3+ content and enhancing the activity. The synergistic effects of La and Co in the bimetallic catalysts are kinetically discussed. In addition, the kinetic and experimental studies revealed that the generated water favors the selectivity but suppresses the activity for the titled reaction. It is found that good activity and excellent selectivity for the (heterocyclic)aromatic alcohols aerobic selective oxidation over the bimetallic catalyst were obtained.

Synthesis, crystal structure, spectral characterization, theoretical studies, and investigation of catalytic activity in selective oxidation of sulfides by oxo-peroxo tungsten(VI) Schiff base complex

A novel oxo–peroxo tungsten(VI) Schiff base complex, [WO(O2)L(CH3OH)], a homogeneous catalyst for sulfoxidation was synthesized by treating WO3 in the presence of H2O2 with a dibasic tridentate (ONO) Schiff base ligand. The complex was characterized by FT–IR, 1H NMR, and 13C NMR spectroscopy. Moreover, the structure of the crystalline tungsten(VI) complex was further investigated by single crystal X-ray diffraction analysis (SC-XRD). The crystal structure analysis revealed that the complex is hepta-coordinated, and metal ion is surrounded by ONO set of the coordinated doubly deprotonated ligand to adopt a distorted pentagonal–bipyramidal geometry. The theoratical calculations of the geometrical parameters, frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP), and natural bond orbital (NBO) analysis of the synthesized compounds utilizing DFT at the B3LYP level of theory at the Def2-TZVP basis set revealed that the predicted data match the experimental results. The main purpose of the current study is to employ the synthesized W complex for its homogeneous catalytic effectiveness for the oxidation of aryl and alkyl sulfides in ethanol by using 30% aqueous H2O2.

Acetylene/Vinylene-Bridged π-Conjugated Covalent Triazine Polymers for Photocatalytic Aerobic Oxidation Reactions under Visible Light Irradiation.

Solar-driven photocatalytic chemical transformation provides a sustainable strategy to produce valuable feedstock, but designing photocatalysts with high efficiency remains challenging. Herein, two acetylene- or vinylene-bridged π-conjugated covalent triazine polymers, A-CTP-DPA and V-CTP-DPE, were successfully fabricated toward metal-free photocatalytic oxidation under visible light irradiation. Compared to the one without acetylene or vinylene bridge, both resulting polymers exhibited superior activity in photocatalytic selective oxidation of sulfides and oxidative coupling of amines; in particular, A-CTP-DPA delivered an optimal photocatalytic performance. The superior activity was attributed to the broadened spectral response range, effective separation, rapid transportation of photogenerated charge carriers, and abundant active sites for photogenerated electrons due to the existence of the acetylene bridge in the framework. This work highlights the potential of acetylene and vinylene bridges in tuning catalytic efficiency of organic semiconductors, providing a guideline for the design of efficient photocatalysts.

Immobilization of polyoxometalates via in-situ protonation and self-gelation of PEG-b-PDMAEMA-b-PTEPM triblock copolymer and its application in selective oxidation

To enrich the building block and function as well as the preparation methodology of metallopolymer system, functioned inorganic polyoxometalate clusters were introduced by using their intrinsic acidity induced multiple interactions with triblock copolymers. In the designed triblock copolymer PEG-b-PDMAEMA-b-PTEPM, the POMs clusters can be immobilized through in-situ protonation of the PDMAEMA block induced electrostatic interaction and the self-gelation of the PTEPM block, while the PEG block can improve the water solubility and dispersion of the final polyoxometalate-based hybrid catalyst (PHC). The selective oxidation activity of PHC is comparable with the homogeneous POMs catalyst as demonstrated by the model reaction of the selective oxidation of methyl phenyl sulfide (MPS) to methyl phenyl sulfoxide (MPSO). By optimizing the ratio between PHC and oxidant H2O2, the selectivity for MPSO can achieve as high as 99% with conversion above 95%. Furthermore, the multiple interactions between POMs and the polymer substrate also enhance the stability of PHC and enable the recycling of PHC. Therefore, the methodology of in-situ protonation and self-gelation by the acidity of POMs provides a facile and general strategy to prepare robust POMs-based metallopolymers, paving a new avenue towards cluster-based materials and devices.

A stable single-atom Zn catalyst synthesized by a ligand-stabilized pyrolysis strategy for selective oxidation of C–H bonds

A ligand-stabilized pyrolysis strategy was developed to fabricate single atom dispersed Zn–N–C catalyst. The fabricated Zn–N–C-900 catalyst showed excellent photocatalytic activity and outstanding stability for ethylbenzene selective oxidation.

Theoretical design principles of metal catalysts for selective ammonia oxidation from high throughput computation

High throughput calculation is performed to reveal the ruling laws of catalytic performance and further screen potential alloy catalysts with high activity and selectivity for selective catalytic oxidation of ammonia (NH3-SCO).

A highly efficient heterogeneous catalyst for selective oxidation of sulfides derived from an open-framework copper borovanadate containing a unique crown-shaped anion.

A novel 3D open-framework copper borovanadate with a unique crown-shaped anion [(VIVO)8(VVO)4B32O64(OH)8]12- and the largest ratio of Cu2+/borovanadate anions (6/1) has been successfully synthesized and systematically studied. The compound not only possesses high stability in a wide pH range of 3.2-10.8 (DMF solution), but also exhibits excellent catalytic activities for selective oxidation of sulfides.

One-pot pyrolysis method to fabricate Co/N co-doped hollow mesoporous spheres with carbon/silica binary shells for selective oxidation of arylalkanes

Hollow mesoporous silica spheres have an excellent application prospect in the field of catalysis due to high specific surface area, tunable pore size, structural stability and void-confinement effect. In this work, rasberry-like Co/N co-doped hollow mesoporous spheres with carbon/silica binary shells were synthesized by a facile one-pot pyrolysis method, and the catalysts with different properties can be obtained easily by adjusting the factors such as the pyrolysis temperature and the introduction approach of the active substance cobalt porphyrin. The results indicated that pyrolysis temperature could exert influence on the specific surface areas and defects of catalysts. Moreover, the active sites introduced through different ways played an important role in utilizing the enrichment effect of reactants originated from the void-confinement effect. As a result, the obtained catalysts showed remarkable activity and stability for selective oxidation of ethylbenzene under moderate reaction condition. Additionally, the optimal catalyst that achieved 95.9% ethylbenzene conversion and 99.3% acetophenone selectivity also exhibited outstanding catalytic performance for lots of arylalkanes. The superior performance was due to the large specific surface area and the well-dispersed active sites stabilized by the hollow structures with carbon/silica binary shells, which could maximize the enrichment of reactants to accelerate the reaction.

N-doped porous carbocatalyst engineering via modulating the crystalline size of ZIF-8 for continuous H2S selective oxidation

Nitrogen-doped porous carbon (NPC) has been considered as an efficient metal-free catalyst for selective oxidation of H2S, but the key factors affecting the reaction performance most are hard to identify due to that the carbocatalyst is usually derived from the complex and uncontrollable synthesis methodology. Herein, we report on the synthesis of NPC derived from the carbonization of high-quality ZIF-8 nanocrystals as the robust carbocatalysts for H2S selective oxidation. By tuning MEIM (2-Methylimidazole)/Zn (II) molar ratio, the precise size of ZIF-8 nanocrystals can be easily controlled and resulted in the NPC particle size range from 0.12 to 1.06 μm. Benefit from the rapid diffusion pathway and full exposure of active N sites, the obtained NPC-8 with particle size of ∼ 0.31 μm exhibits superior catalytic performance on H2S selective oxidation, achieving an excellent catalytic conversion rate of 99% as well as stability (> 100 h) at 190 °C. Combined with characterization results and reaction parameter experiments, it could be induced that the catalytic activity of H2S selective oxidation could be mainly affected by the size of ZIF nanocrystals, beside that, the developed micro-/mesopores framework and abundant N sites also contribute to improve the intrinsic activity of NPC.

Selective photocatalytic oxidation of sulfides with dioxygen over carbazole–fluorene conjugated microporous polymers

One sustainable concept emerges to implement the selective oxidation of sulfides with dioxygen (O2) at ambient conditions and has received increasing attention. As such, three donor–acceptor (D–A) type conjugated microporous polymers (CMPs) were connected via robust CC bonds prepared from FeCl3-promoted polymerization of monomers of 3,6-di(9H-carbazol-9-yl)-9H-fluorene with the 9H position of the fluorene moiety occupied by 1,1′-biphenyl-, difluoro-, or keto- group, furnishing 9,9′-(9,9′-spirobi[fluorene]-2,7-diyl)-bis-9H-carbazole-CMP (SFC-CMP), 9,9′-(9,9-difluoro-9H-fluorene-2,7-diyl)bis(9H-carbazole)-CMP (FFC-CMP), and 2,7-di(carbazol-9-yl)-fluoren-9-one-CMP (OFC-CMP), respectively. These three carbazole–fluorene CMPs could implement blue light-driven highly selective oxidation of sulfides into sulfoxides with O2 in methanol (CH3OH). Intriguingly, the SFC-CMP imparted the best photocatalytic activity for selective oxidation of sulfides in a broad scope. Besides, the SFC-CMP photocatalyst could be fully recovered even outperforming the fresh one. This work highlights that the properties of CMPs could be regulated by the D–A units like carbazole–fluorene to execute selective chemical transformations ambiently.

CdS(ZB)/CdS(WZ)/Ni-BTC photocatalytic selective oxidation of benzyl alcohol to benzaldehyde coupled with hydrogen evolution

Development of difunctional photocatalyst for both hydrogen production and high value-added fine chemicals is of great industrial significance. Cubic crystal phase zinc blende CdS(ZB) and hexagonal crystal phase wurtzite CdS(WZ) in CdS(ZB)/CdS(WZ)/Ni-BTC (BTC = 1,3,5-benzene tricarboxylic acid) composites can form intergrowth homojunction to improve the photoelectron-hole separation efficiency, so that the composites show excellent catalytic activity in photocatalytic selective oxidation of benzyl alcohol to benzaldehyde coupled with hydrogen evolution reaction. The conversion of benzyl alcohol can up to 99.0%, the yield of benzaldehyde is 90.2%, and the yield of hydrogen is 2.891 mmoL·g−1·h−1. Meanwhile, styrene was reduced by hydrogen produced via photocatalytic oxidation benzyl alcohol using D2O as reaction solvent. The results demonstrate clearly that 41.6% of H2 come from benzyl alcohol, and 58.4% of D2 come from D2O by analysis of the benzene ethane product. The catalytic mechanism is speculated to be that the benzyl alcohol can simultaneous produce benzaldehyde and H2 by holes oxidation and dehydrogenation, and electron reduce the intrinsic hydrogen ion in water to H2. These results enrich the mechanism of photocatalytic benzyl alcohol oxidation coupled with hydrogen evolution, and provide a new experimental and technical strategy for the design and synthesis of dual-function photocatalysts.

Efficient photocatalytic toluene selective oxidation over Cs3Bi1.8Sb0.2Br9 Nanosheets: Enhanced charge carriers generation and C–H bond dissociation

Inert C–H bonds activation at room temperature has been regarded as the control step in photocatalytic generation of valuable products from hydrocarbons. Herein, lead-free perovskite Cs3Bi1.8Sb0.2Br9 nanosheets with a proper amount of Sb in Cs3Bi2Br9 not only improves optical absorption due to anomalous band gap behavior, but also promotes the generation of holes (h+). The convergence of h+ on the surface of Cs3Bi1.8Sb0.2Br9 is crucial for the dissociation of toluene C(sp3)–H bond, which was proved by the density functional theory calculation and isotopic labelling results. The excellent activity in photocatalytic selective oxidation of toluene with a conversion rate of 5.83 mmol g−1h−1 under visible light is the highest ever achieved. This work sheds light on the modification of halide perovskites through the regulation of B-site cations for photocatalytic applications.

Enhanced Photocatalytic Activity for Selective Oxidation of Toluene over Cubic–Hexagonal CdS Phase Junctions

Enhanced Photocatalytic Activity for Selective Oxidation of Toluene over Cubic–Hexagonal CdS Phase Junctions

TEMPO-Functionalized Nanoreactors from Bottlebrush Copolymers for the Selective Oxidation of Alcohols in Water.

Polymeric nanoreactors in water fabricated by the self-assembly of amphiphilic copolymers have attracted much attention due to their good catalytic performance without using organic solvents. However, the disassembly and instability of relevant nanostructures often compromise their potential applicability. Herein, the preparation of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-containing nanoreactors by the self-assembly of amphiphilic bottlebrush copolymers has been demonstrated. First, a macromonomer having a norbornenyl polymerizable group was prepared by RAFT polymerization of hydrophobic and hydrophilic monomers. The macromonomer was further subjected to ring-opening metathesis polymerization to produce an amphiphilic bottlebrush copolymer. Further, TEMPO, as a catalyst, was introduced into the hydrophobic block through the activated ester strategy. Finally, TEMPO-functionalized polymeric nanoreactors were successfully obtained by self-assembly in water. The nanoreactors exhibited excellent catalytic activities in selective oxidation of alcohols in water. More importantly, the reaction kinetics showed that the turnover frequency is greatly increased compared to that of the similar nanoreactor prepared from liner copolymers under the same conditions. The outstanding catalytic activities of the nanoreactors from bottlebrush copolymers could be attributed to the more stable micellar structure using the substrate concentration effect. This work presents a new strategy to fabricate stable nanoreactors, paving the way for highly efficient organic reactions in aqueous solutions.

Z-scheme g-C3N4/Fe2O3 for efficient photo-oxidation of benzylamine under mild conditions

As an important intermediate, imine is widely used in industrial chemistry. The photocatalytic oxidation of amines to form imines is a green and economical method. But it remains a challenge for the efficient transformation under mild conditions. Herein, a Z-scheme carbon nitride (CM)-Fe2O3 heterojunction photocatalyst was synthesized by in-situ preparation of Fe2O3 nanoparticles on two-dimensional CM nanosheets. The as-prepared catalyst exhibited efficient photocatalysis activity in selective oxidation of benzylamine to N-benzylidene benzylamine. Under ambient air and room temperature, the selectivity and conversion rate both can reach 99.9%, and the corresponding turnover frequency value reaches up to 9.99 mmol g−1 h−1, superior to the most of heterogeneous photocatalysts reported in previous literatures. The excellent catalytic activity of the modified CM material may be due to the enhanced absorption of visible light and the improved photogenerated carrier separation and migration rate, and the Z-scheme mechanism also retains the strong oxidation and reduction ability of the composite material. This work will provide a promising and practical method to promote the photocatalytic conversion of solar-driven organics.