Surface Active Oxygen Species Research Articles

Doping SnO2 with metal ions of varying valence states: discerning the importance of active surface oxygen species vs. acid sites for C3H8 and CO oxidation.

To elucidate the valence state effect of doping cations, Li+, Mg2+, Cr3+, Zr4+ and Nb5+ with radii similar to Sn4+ (CN = 6) were chosen to dope tetragonal SnO2. Cr3+, Zr4+ and Nb5+ can enter the SnO2 lattice to produce solid solutions, thus creating more surface defects. However, Li+ and Mg2+ can only stay on the SnO2 surface as nitrates, thus suppressing the surface defects. The rich surface defects facilitate the generation of active O2-/Oδ- and acid sites on the solid solution catalysts, hence improving the reactivity. On the solid solution catalysts active for propane combustion, several reactive intermediates can be formed, but are negligible on those with low activity. It is confirmed that for propane combustion, surface acid sites play a more vital role than active oxygen sites. Nevertheless, for CO oxidation, the active oxygen sites play a more vital role than the acid sites.

Boosting propane combustion over Pt/WO3 catalyst by activating interface oxygen species

Surface active oxygen species in heterogeneous catalyst material is very vital for driving catalytic volatile organic compounds (VOCs) oxidation, but it still remains challenging to effectively modulate such active oxygen species. Herein, the interfacial oxygen species in Pt/WO3 catalyst is conveniently activated by a heating treatment under nitrogen flow. The obtain Pt/WO3-N2-T (T = 200, 400, 600, represents the calcination temperature) shows much superior catalytic activity than the bare Pt/WO3 catalyst, particularly for the Pt/WO3-N2-400 catalyst with T95 of only 250 °C (T95 of Pt/WO3 = 350 °C). The changes of catalyst structure during heating treatment in nitrogen flow contributes to the improved activity, including re-dispersed WO3 support and Pt nanoparticles. More importantly, the surface oxygen species in the Pt/WO3-N2-400 catalyst is more active than that of the bare Pt/WO3 catalyst, which is generated by removing hydroxyl groups and its residual oxygen species activated by nearby Pt species. These novel findings provide the strategy to rationally activate surface oxygen in the heterogeneous catalyst materials for catalytic oxidation reaction.

Promotion of Rh-based La2Zr2O7 type catalysts with the transition metals to improve sulfur-tolerance in diesel reforming

Several Rh-based La2Zr2O7 type catalysts promoted by the transition metals (Mn, Fe, and Co respectively) were synthesized and used to reform n-hexadecane (a diesel surrogate) that contains 50 ppm dibenzothiophene for hydrogen production. Compared to Co-LaZrRh and Mn-LaZrRh, the Fe-LaZrRh catalyst exhibited the best hydrogen extraction capability and sulfur tolerance. This is probably due to the introduction of Fe, which not only enhances the Rh dispersion, but also facilitates the formation of electron-deficient Rh sites and the generation of oxygen vacancies. Additionally, electron-deficient Rh sites can hinder the formation of an irreversible sulfur-metal bond, thus resulting in better sulfur tolerance and thermal stability. Finally, the generated oxygen vacancies may also activate steam to form surface active oxygen species, which help remove the deposited carbon on the catalyst surface. In summary, the developed Fe-LaZrRh catalyst performed the best in the steam reforming of n-hexadecane containing 50 ppm sulfur, which deserves further exploration for future applications.

Oxygen adsorption capability and electrochemical properties induced by oxygen vacancies in cerium-doped LaFeO3 perovskite oxide

The effect of Ce doping on the electrochemical properties of LaFeO3 perovskite oxides was investigated in terms of the oxygen adsorption capability and polarization resistance. The Ce-doped LaFeO3 perovskite oxide had a single perovskite phase with an orthorhombic structure. The presence of oxygen vacancies was confirmed by EPR spectra and O 1 s core-level spectra. An O2 temperature-programmed desorption profile demonstrated an increase in the quantity of surface-active oxygen species, with LCFO5 exhibiting the highest oxygen adsorption capability. The area-specific resistance gradually decreased with the cerium doping from 11.36 Ωcm2 (LFO) to 4.65 Ω cm2 (LCFO5). A notable decrease of 68 % was confirmed in the polarization resistance related to the mass transfer, from 7.66 Ωcm2 (LFO) to 2.44 Ωcm2 (LCFO5). This significant decrease indicates an enhanced oxygen reduction reaction activity, which is attributed to the accelerated oxygen adsorption reaction.

An Experimental and Density Functional Theory Simulation Study of NO Reduction Mechanisms over Fe0 Supported on Graphene with and without CO.

NO reduction over highly dispersed zerovalent iron (Fe0) supported on graphene (G), with and without the presence of CO in the reacting stream, was systematically studied using a fixed-bed reactor, and the reaction mechanism was examined with the aid of in situ Fourier transform infrared (FTIR) spectroscopy and density functional theory (DFT) calculations. The in situ FTIR results showed that NO adsorbed on the Fe0 site is reduced to form active surface oxygen species (O*), which is then reduced by carbon in graphene to form CO2. The presence of CO in the reacting stream helps to reduce the oxidized Fe(O) sites to regenerate Fe0 sites, making NO reduction easier. It was revealed that NO and CO2 are easily adsorbed on the active surface oxygen species (O*) to form nitrate and carbonate, inhibiting their reduction by CO and deactivating the catalyst. The DFT calculations results suggest that the role of Fe is to reduce the energy barrier of the NO adsorption and decomposition, which controls the formation of active surface oxygen species and N2. The combined FTIR and DFT results offer new insights into the possible mechanism of catalytic NO reduction over graphene loaded with Fe, with and without CO.

Facile synthesis of highly dispersed Ir/LaFeO3 catalysts for propene total oxidation

A series of Ir/LaFeO3 catalysts calcined at 300–600 °C were synthesized by a solvent-free method and tested for propene total oxidation. Various characterizations depicted that iridium was well-dispersed on LaFeO3 with no detectable iridium-related particles or aggregates. The loading of iridium hardly changed the structural and textural properties of LaFeO3, but greatly enhanced the low-temperature reducibility and oxygen mobility, leading to superior propene oxidation activity. For Ir/LaFeO3 series, the catalytic activity decreased as the calcination temperature increased, due to the declined reducibility and active oxygen species content. Ir/LaFeO3-300 was demonstrated to be the optimal catalyst with the best propene oxidation performance (T90 = 246 °C), excellent long-term stability, and decent water-resistance. Treating Ir/LaFeO3-300 in a reducing atmosphere further improved its catalytic performance by enhancing low-temperature reducibility and increasing surface-active oxygen species. Overall, this study provides insights into the synthesis of highly efficient and stable iridium-based catalysts for VOCs oxidation.

Insights into the catalytic performance of LDHs-derived CoAlO oxides with different anions intercalation for propane total oxidation

Constructing effective and stable non-noble metal catalysts is of great significance and prospect for catalytic oxidation of stable light alkanes at low temperature. Herein, the CoAlO oxide catalysts derived from the CoAl layered double hydroxides (LDHs) intercalated with CO32–, CH3COO– (Ac), SO42-, NO3– and citrate (CA) anions were prepared, and their catalytic performances for propane oxidation were investigated. Among all CoAlO catalysts, the CoAlO-Ac-3 catalyst (CH3COO– anion intercalation) exhibited better catalytic activity for propane oxidation (T90 = 300 °C), with the highest reaction rate (2.79 × 10-7 mol g−1 s−1) and TOF value (0.13 × 10-3 s−1) at 240 °C. Characterization results revealed that the interlayer anions affected the valence distribution of metals and surface active oxygen species, and CH3COO– anion intercalation CoAlO-Ac catalyst showed the highest Co3+/Co2+ molar ratio and active oxygen species. Combining with Raman and in-situ DRIFTS results, the lattice distortion of catalyst caused by the interlayer anions promoted the migration of active oxygen species, thus accelerating the propane adsorption and activation. Meanwhile, CoAlO-Ac-3 catalyst exhibited excellent stability and water resistance for propane oxidation.

Arsenic removal from coal-fired flue gas by metal oxides modified wood chips coke: Experimental and DFT study

Coal-fired power plant is one of the main anthropogenic arsenic emission sources, where gaseous As2O3 is the main form in the flue gas to the atmosphere. In this work, a series of metal salt impregnated wood chips coke (Me-BC) were developed for As2O3 removal from flue gas, which selected BC with low cost and high arsenic removal potential as the carrier and modified by metal nitrate through impregnation and pyrolysis to load active components. The results indicate that As2O3 removal performance of the Me-BC obeys Fe-BC-0.15 > BC > Al-BC-0.15 > Ca-BC-0.15 > K-BC-0.15 under the basic flue gas composition (N2 + O2 + CO2) at 150℃, with the highest As2O3 removal capacity (141.5 μg/g) and efficiency (92.9%) for Fe-BC-0.15 compared to 92.4 μg/g, 60.7% of the BC. The arsenic removal ability of Fe-BC firstly increases and then decreases as Fe(NO3)3 impregnation concentration increases with its maximum value at 0.15 mol/L. Generally, the NO has a significant inhibitory effect on the arsenic removal of Fe-BC-0.15 due to consumption of surface active oxygen species by or the competitive adsorption between NO and As2O3. Low-concentration SO2 complete with As2O3 for the adsorption on active sites while high-concentration SO2 will promote SO3 and Oβ formation which benefits for As2O3 capture. Overall, Oɑ and Oβ and C-O play an important promoting role in the arsenic removal by adsorbents. DFT calculations indicates that C-O have strongest adsorption energy for As2O3 among oxygen-containing functional groups. The adsorption of SO2 and NO on naked BC and BC-O is easier than As2O3. Both Fe2O3 and BC play an important role in the arsenic removal process by Fe-BC-0.15.

Elemental mercury removal over MnOx-CoOx-modified HZSM-5 adsorbents: Performance and characterizations

In this study, MnOx-CoOx-modified HZSM-5 sorbents were prepared via the ultrasound-assisted impregnation method for Hg0 removal from the coal-fired flue gas. With the introduction of MnOx-CoOx, the Hg0 removal performance exhibited an increasing trend. Given that the mass content of MnOx-CoOx and the molar ratio of Mn/Co were fixed to 12 wt% and 1:3, the sorbent exhibited a relatively high Hg0 removal efficiency of 81% at 150 °C. Compared to virgin MnOx- or CoOx-modified HZSM-5 sorbent, the synergistic effect between MnOx and CoOx generated abundant surface acid sites and active oxygen species, which facilitated the adsorption of Hg0 and accelerated the oxidation of the adsorbed Hg0. Throughout the Hg0 capture cycles, Mn4+ and Co3+ acted as the active sites with HgO being the end product. Among the various gas constitutes, both O2 and NO demonstrated promotional effect on Hg0 removal, while SO2 interfered with the reaction to some degree. With the co-introduction of NO and SO2, an Hg0 removal efficiency of ∼94% was attained. Given its excellent recyclability, this sorbent system shows promising application potential.

Excellent Performance and Feasible Mechanism of ErOx-Boosted MnOx-Modified Biochars Derived from Sewage Sludge and Rice Straw for Formaldehyde Elimination: In Situ DRIFTS and DFT

To avoid resource waste and environmental pollution, a chain of ErOx-boosted MnOx-modified biochars derived from rice straw and sewage sludge (EryMn1-y/BACs, where biochars derived from rice straw and sewage sludge were defined as BACs) were manufactured for formaldehyde (HCHO) elimination. The optimal 15%Er0.5Mn0.5/BAC achieved a 97.2% HCHO removal efficiency at 220 °C and exhibited favorable EHCHO and thermal stability in a wide temperature window between 180 and 380 °C. The curbed influences of H2O and SO2 offset the boosting effect of O2 in a certain range. Er–Mn bimetallic-modified BACs offered a superior HCHO removal performance compared with that of BACs boosted using Er or Mn separately, owing to the synergistic effect of ErOx and MnOx conducive to improving the samples’ total pore volume and surface area, surface active oxygen species, promoting redox ability, and inhibiting the crystallization of MnOx. Moreover, the support’s hierarchical porous structure not only expedited the diffusion and mass transfer of reactants and their products but also elevated the approachability of adsorption and catalytic sites. Notably, these prominent features were partly responsible for the outstanding performance and excellent tolerance to H2O and SO2. Using in situ DRIFTS characterization analysis, it could be inferred that the removal process of HCHO was HCHOad → dioxymethylene (DOM) → formate species → CO2 + H2O, further enhanced with reactive oxygen species. The DFT calculation once again proved the removal process of HCHO and the strengthening effect of Er doping. Furthermore, the optimal catalytic performance of 15%Er0.5Mn0.5/BAC demonstrated its vast potential for practical applications.

Enhanced moisture resistance and catalytic stability of ethylene oxidation at room temperature by the ultrasmall MnOx cluster/Pt hetero-junction

Ethylene elimination can effectively inhibit the rapid aging of fruits and vegetables in storage and transportation. Improving the low-temperature activity, moisture resistance, and stability of Pt based catalysts is a challenge for catalytic oxidation of ethylene which is an effective elimination method. Herein, we constructed ultrasmall MnOx cluster (< 1 nm) on Pt particles via an alloy in situ transformation strategy, which created a large number of MnOx/Pt interfaces. Among all of the samples, 1.89Pt2.20Mn/TiO2 showed the highest catalytic activity in the oxidation of ethylene at a space velocity of 20,000 mL/(g h): T50% = 34 oC and T90% = 43 oC, specific reaction rate at 35 oC = 33.0 µmol/(gPt s), and turnover frequency at 35 oC = 6.5 × 10–3 s−1. In addition, Pt2.20Mn/TiO2 also exhibited better water resistance and stability than Pt/TiO2. The results of XPS, H2O-TPD, C2H4-TPD, in situ DRIFTS, and H218O isotopic tracing characterization revealed that the MnOx/Pt interfacial sites accelerated desorption of CO2 and enhanced the activation of surface active oxygen species (O2 to O22−). Meanwhile, the numerous interfaces provide more active sites for ethylene adsorption and activation, reducing the inhibitory effect of adsorbed water on ethylene adsorption. It was concluded that the prohibited CO2 adsorption, and increased adsorbed oxygen species were responsible for the excellent catalytic performance and good stability of 1.89Pt2.20Mn/TiO2, while the more active sites for ethylene adsorption and activation were responsible for the good water resistance of 1.89Pt2.20Mn/TiO2.

Fabrication of highly dispersed Pd-Mn3O4 catalyst for efficient catalytic propane total oxidation

Adjusting the interaction between dual active components for enhancing volatile organic compounds (VOCs) degradation is an effective but still challenging means of air pollution control. Herein, a limited pyrolysis oxidation strategy was adopted to prepare Pd-Mn3O4 spinel catalysts with uniform morphology and active component dispersion. Among these, 1.08Pd-Mn3O4 presented the highest catalytic efficiency with a T90 value of 240 °C, which was 94 °C lower than that of Mn3O4. Characterization and density functional theory (DFT) calculation results revealed that the strong metal-support interaction (SMSI) effect between Pd and Mn3O4 promoted the redistribution of surface charges, thus strengthening the oxidation-reduction ability of the active sites. Moreover, the SMSI effect led to a better migration of surface oxygen species, and boosted the generation of active surface oxygen species. Simultaneously, the Pd catalyst further reduced the energy barrier in the initial stage of the dehydrogenation of propane. Overall, this study provided a novel design strategy for dual active components catalysts with SMSI effect and extended the application of these catalysts in the important field of VOCs elimination.

Toluene and 2-propanol mixture oxidation over Mn2O3 catalysts: Study of inhibition/promotion effects by in-situ DRIFTS

Three Mn2O3 catalysts were synthetized by different methods, characterized and tested in toluene and 2-propanol (iPrOH) oxidation in single and binary component mixture. In single VOC media, the catalytic activity was strongly influenced by the specific surface area, low-temperature reducibility and active surface-oxygen species. In the binary VOCs mixture oxidation, light-off curves were shifted to lower temperatures, suggesting a promoting effect on the catalytic activity for toluene and iPrOH oxidation. The acetone production in binary mixture was also shifted to lower temperatures. The obtained results were rationalized based on the different polarity of the VOCs, the available adsorbed oxygen and the exothermic character of the VOCs combustion. These promoting effects were pointed out by in-situ DRIFTS measurements, in which the pre-adsorption of any of these two VOCs affected the adsorption/reaction of the other. For the first time, in-situ DRIFTS has been applied to elucidate the reaction mechanisms of the oxidation of toluene/2-propanol mixture on Mn2O3, which allowed to correlate the surface phenomena and the catalytic performance.

Novel Cs–Mg–Al mixed oxide with improved mobility of oxygen species for passive NOx adsorption

The development of passive NOx adsorbers with cost-benefit and high NOx storage capacity remains an on-going challenge to after-treatment technologies at lower temperatures associated with cold-start NOx emissions. Herein, Cs1Mg3Al catalyst prepared by sol–gel method was cyclic tested in NOx storage under 5 vol% water. At 100 °C, the NOx storage capacity (1219 μmol g−1) was much higher than that of Pt/BaO/Al2O3 (610 μmol g−1). This provided new insights for non-noble metal catalysts in low-temperature passive NOx adsorption. The addition of Cs improved the mobility of oxygen species and thus improved the NOx storage capacity. The XRD, XPS, IR spectra and in situ DRIFTs with NH3 probe showed an interaction between CsOx and AlOx sites via oxygen species formed on Cs1Mg3Al catalyst. The improved mobility of oxygen species inferred from O2-TPD was consistent with high NOx storage capacity related to enhanced formation of nitrate and additional nitrite species by NOx oxidation. Moreover, the addition of Mg might improve the stability of Cs1Mg3Al by stabilizing surface active oxygen species in cyclic experiments.

Constructing γ-MnO2 with abundant oxygen vacancies by a chelating agent-assistant strategy to achieve high-efficient conversion of NO to NO2

To date, the exploitation of non-noble materials of high-efficiency and low-temperature conversion of NO to NO2 still existed as a challenging task due to high cost of current Pt-based commercial catalysts. Herein, we employed a chelating agent-assistant strategy to regulate the content of oxygen vacancy over γ-MnO2 catalysts, which were further used for NO oxidation. Benefiting from the structure-directing effect of tartaric acid, the resultant locus-shaped γ-MnO2 catalyst with abundant oxygen vacancies showed a remarkable low-temperature catalytic activity (T50 and T92 of 127 and 225 °C; respectively), which was superior to unmodified γ-MnO2 sample (T50 at 189 °C) and those recently reported good-performing NO oxidation catalysts. An array of characterization results revealed that an extended capping by means of chelating agents could effectively weaken the MnO bond strength and promote the formation of oxygen vacancy (OVs), thus tremendously increase the amount of surface-active oxygen species. Moreover, theoretical calculation demonstrated that an enriched OVs concentration could enhance the reactivity of surface lattice oxygen by reducing the formation energy of OVs, further accelerating reaction rate of the adsorption/activation of O2 molecules and thus bringing about an outstanding low-temperature catalytic activity. This study highlighted the potential of chelating agents in the design of high-efficient catalysts for environmental remediation and beyond.

Tailoring Oxygen Vacancies and Active Surface Oxygen Species in Copper-Doped MnO2 Catalysts for Total Catalytic Oxidation of VOCs

Catalytic oxidation has been considered an essential route to tackle volatile organic compounds (VOCs)-driven pollution. To this point, surface engineering has emerged as a robust pathway to promote the efficiency of MnO2-based materials toward VOC oxidation. However, regulating such surface properties has been a critical challenge. This investigation attempts to tailor surface oxygen vacancies and active surface oxygen for the total catalytic oxidation of various VOCs (e.g., formaldehyde, isopropanol, and toluene) via doping copper into cryptomelane and birnessite-type MnO2 catalysts. The catalysts are synthesized by a novel facile successive redox precipitation method between KMnO4 and an ethanol solution containing copper nitrate precursors, followed by annealing. It turns out that the low amount of Cu dopants, corresponding to the copper-to-manganese ratio of 0.17 (RCu/Mn = 0.17), generates a tunnel-structured cryptomelane-type MnO2 with strong bulk oxygen mobility. Such a crystalline structure exhibits the best catalytic performance for the total catalytic oxidation of toluene. The higher copper loading (RCu/Mn = 0.27–0.34) drives the formation of Cu-doped layered birnessite-type MnO2 materials containing rich oxygen vacancies and high active surface oxygen species. Those catalysts promote the oxidation of isopropanol and formaldehyde, respectively. To this end, oxygen vacancies and surface oxygen species crucially steer the molecular oxygen activation and interactions toward adsorbed oxygen species, significantly promoting the total oxidation of isopropanol and formaldehyde, respectively. The explored finding could disclose an outstanding platform toward highly selective and efficient oxidation of VOCs.

Construction of α-MnO2/g-C3N4 Z-scheme heterojunction for photothermal synergistic catalytic decomposition of formaldehyde

Formaldehyde (HCHO), as the most common indoor air pollutant, undoubtedly poses a huge threat to people's health. It is of practical importance to achieve complete decomposition of HCHO to harmless CO2 at room temperature. Herein, α-MnO2/g-C3N4 Z-scheme heterojunction was constructed through the in-situ growth of α-MnO2 nanowires on the surface of g-C3N4 nanosheets. Owing to the construction of Z-scheme heterojunction, α-MnO2/g-C3N4 composite exhibits excellent photothermal catalytic activity, achieving complete mineralization of HCHO with the illumination of 191 mW/cm2 solar-light at GHSV of 180 L/gcat·h. Particularly, even under one sun and visible light radiation, the α-MnO2/g-C3N4 composite can still maintain 60% and 68% HCHO conversion, respectively. The formation of α-MnO2/g-C3N4 Z-scheme heterojunction not only effectively inhibits the photogenerated electron-hole pairs recombination, but also overcomes the band defects of the individual component. Furthermore, the mechanism of the photothermal catalysis of α-MnO2/g-C3N4 composite was discovered to be thermal-assisted photocatalytic process rather than solar-light driven thermalcatalysis. On the one hand, the thermal energy generated from light radiation can accelerate the migration of photo-generated carriers and improve the separation efficiency of photogenerated electrons from vacancies; on the other hand, it can decrease the activation energy of lattice oxygen and produce more surface-active oxygen species. This work provides cost-effective strategies and suggestions for decomposing HCHO and other VOCs in indoor air at room temperature.

Non-Thermal Plasma Incorporated with Cu-Mn/γ-Al2O3 for Mixed Benzene Series VOCs’ Degradation

In this work, a coaxial dielectric barrier discharge (DBD) reactor was constructed to degrade the mixture of toluene and o-xylene, two typical benzene series. The Cu-MnO2/γ-Al2O3 series catalysts prepared by redox and impregnation methods were filled into the plasma device to degrade VOCs synergistically and explore the degradation effect. The experimental results showed that the introduction of a Cu-doped MnO2 catalyst significantly improved the pollutants’ removal efficiency and CO2 selectivity, and greatly inhibited the formation of by-products. Among them, Cu0.15Mn/γ-Al2O3 showed the highest removal efficiency (toluene was 100% and o-xylene was 100%), and the best CO2 selectivity (92.73%). The XRD, BET, XPS and SEM results confirmed that the synergistic effect between Cu and Mn in the Cu-Mn solid solution could promote the amount and reducibility of the surface active oxygen species, which improved the catalytic performance. Finally, the toluene and o-xylene decomposition pathways in the NTP catalytic system were speculated according to the detected organic matter. This work provides a theoretical and experimental basis for the application of DBD-catalyzed hybrid benzene series VOCs.

Insights into the Role of Nanorod-Shaped MnO2 and CeO2 in a Plasma Catalysis System for Methanol Oxidation.

Published papers highlight the roles of the catalysts in plasma catalysis systems, and it is essential to provide deep insight into the mechanism of the reaction. In this work, a coaxial dielectric barrier discharge (DBD) reactor packed with γ-MnO2 and CeO2 with similar nanorod morphologies and particle sizes was used for methanol oxidation at atmospheric pressure and room temperature. The experimental results showed that both γ-MnO2 and CeO2 exhibited good performance in methanol conversion (up to 100%), but the CO2 selectivity of CeO2 (up to 59.3%) was much higher than that of γ-MnO2 (up to 28.6%). Catalyst characterization results indicated that CeO2 contained more surface-active oxygen species, adsorbed more methanol and utilized more plasma-induced active species than γ-MnO2. In addition, in situ Raman spectroscopy and Fourier transform infrared spectroscopy (FT-IR) were applied with a novel in situ cell to reveal the major factors affecting the catalytic performance in methanol oxidation. More reactive oxygen species (O22-, O2-) from ozone decomposition were produced on CeO2 compared with γ-MnO2, and less of the intermediate product formate accumulated on the CeO2. The combined results showed that CeO2 was a more effective catalyst than γ-MnO2 for methanol oxidation in the plasma catalysis system.

Robust Bio-derived Polyoxometalate Hybrid for Selective Aerobic Oxidation of Benzylic C(sp3)–H Bonds

Utilization of natural resources to construct functional catalytic materials for challenging organic reactions is of great importance in the chemical community, which has achieved significant attention. Herein, we describe the synthesis of a robust bio-derived polyoxometalate (POM) hybrid by the reaction of the naturally occurring phytic acid (PhyA) with MoO3, and the obtained hybrid was denoted PhyA–Mo. Systematic studies revealed that the multi-phosphate structure of PhyA enabled the synthesized PhyA–Mo to simultaneously possess a higher concentration of surface-active oxygen species and more negatively charged Mo sites, which played the role of catalytically active sites for aerobic oxidation. These two types of active sites together enabled the PhyA–Mo to show outstanding catalytic activity for aerobic oxidation of benzylic C(sp3)–H in different substrates to generate various carbonyl compounds without using any additional initiator. Importantly, the fact of realizing aerobic oxidation of benzylic C(sp3)–H bonds efficiently over POM-based materials in the absence of any radical initiator represented the main finding and the major breakthrough. Especially, this work provided a general and useful strategy to improve the catalytic performance of POM-based materials by using phosphoric acids containing multi-phosphate groups.