N-doped Catalysts Research Articles

Photocatalytic degradation of flumequine by N-doped TiO2 catalysts under simulated sunlight

Flumequine (FLU) is one of the most used fluoroquinolone antibiotics in intensive aquaculture, however, it has become a typical pollutant in water environment at present due to inappropriate use. Therefore, it is necessary to develop facile techniques for efficient degradation of FLU. In this work, three N-doped TiO2 photocatalysts were synthesized for degradation of FLU. The obtained photocatalysts were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectrum and UV-Vis diffuse reflection spectra (UV-Vis-DRS). The XRD and XPS results from NH4NO3-doped catalyst (TiO2/AN) confirmed that NO3<sup>-</sup> ions were successfully incorporated into the lattice of TiO2. The TiO2/AN sample exhibited higher photocatalytic performance than other N-doped catalysts under simulated sunlight irradiation, and 100% removal efficiency of FLU was achieved after 4 hours of illumination. The photogenerated holes (h<sup>+</sup>) and hydroxyl radicals (<sup>•</sup>OH) are main reactive species involved in the photocatalytic degradation of FLU. Eight intermediates for photocatalytic degradation of FLU were detected and their toxicities to aquatic organisms were predicted. This study might have important implications for further research on the removal of fluoroquinolone antibiotics in wastewater.

Nitrogen-Doped Carbide-Derived Carbon/Carbon Nanotube Composites As Cathode Catalysts for Anion Exchange Membrane Fuel Cell Application

Due to the increasing energy consumption, there is a need for renewable energy production devices. Low temperature fuel cells are among the possible options, but their performance is limited by the sluggish kinetics of the electrochemical oxygen reduction reaction (ORR) at the cathode. The most efficient electrocatalysts for the ORR are based on expensive and scarce noble metals, mainly platinum. As more sustainable replacements, various non-precious metal or entirely metal-free catalysts could be used. The latter ones include heteroatom-doped nanocarbons.1,2 Herein, a composite of carbide-derived carbon and carbon nanotubes (CDC/CNT) is doped with nitrogen by pyrolyzing of a mixture containing CDC, CNT and a nitrogen precursor at 800 °C. A composite of carbons were chosen on the premise of obtaining a feasible structure with both micro- and mesopores, which should be beneficial in the anion exchange membrane fuel cell (AEMFC) application. Four different precursors of nitrogen (cyanamide, dicyandiamide, urea or melamine) were used and compared in order to find the most suitable one.3 For the physico-chemical characterization of the catalysts SEM, XPS, Raman spectroscopy and N2 adsorption studies were applied. These proved indeed that a novel carbon structure was formed and the doping with nitrogen was successful with all four precursors (≥3 at% of N). The electrocatalytic activity of the four N-doped catalyst materials was studied in 0.1 M KOH using RDE and RRDE methods. The four N-CDC/CNT catalyst materials exhibited virtually the same and good activity toward the ORR. In order to assess the possible application of the N-CDC/CNT material, it was employed as a cathode catalyst in AEMFC together with a HMT-PMBI4 membrane. The tests were conducted at different conditions and the best performance with peak power density of 310 mW cm–2 was obtained at 70 °C with 1 bar back pressure (Figure 1). This good performance shows that the metal-free N-CDC/CNT materials are promising cathode catalysts for the AEMFC application.3 References A. Sarapuu, E. Kibena-Põldsepp, M. Borghei, and K. Tammeveski, J. Mater. Chem. A, 6, 776-804 (2018).C.Z. Zhu, H. Li, S.F. Fu, D. Du, and Y.H. Lin, Chem. Soc. Rev., 45, 517-531 (2016)J. Lilloja, E. Kibena-Põldsepp, A. Sarapuu, A. Kikas, V. Kisand, M. Käärik, M. Merisalu, A. Treshchalov, M. Rähn, J. Leis, V. Sammelselg, Q. Wei, S. Holdcroft, and K. Tammeveski, Appl. Catal., B, 272, 119012 (2020).A.G. Wright, J.T. Fan, B. Britton, T. Weissbach, H.F. Lee, E.A. Kitching, T.J. Peckham, and S. Holdcroft, Energy Environ. Sci., 9, 2130-2142 (2016). Figure 1

Kelp-derived N-doped biochar activated peroxymonosulfate for ofloxacin degradation

N-doped carbon materials have been proven to be effective catalysts for activating peroxymonosulfate (PMS). Marine algae biomass is rich in nitrogenous substances , which can reduce the cost of N-doping process and can obtain excellent N-doped catalysts cheaply and easily. In this study, kelp biomass was selected to prepare N-doped kelp biochar (KB) materials. The high defect degree, high specific surface area, and participation of graphite N make KB have excellent catalytic degradation ability. The KB degraded 40 mg/L ofloxacin (OFL) close to 100% within 60 min, applied with PMS. Through quenching experiments and electron paramagnetic resonance spectroscopy, the degradation process dominated by non-radical pathways was determined. At the same time, O2·- and 1O2 were closely related, and a significant impact of quenching O2·- on the reaction was observed. The non-radical approach made the system excellent performance over a wide pH range and in the presence of multiple anions. The experiments of reusability confirmed the stability of the material. Its catalytic performance was restored after low-temperature pyrolysis. This research supports the use of endogenous nitrogen in biomass. It provides more options for advanced oxidation process application and marine resource development.

Nitrogen-doped Pt3Co intermetallic compound nanoparticles: A durable oxygen reduction electrocatalyst

Pt-based ordered alloy catalysts have been extensively investigated to improve the catalytic performance for proton exchange membrane fuel cells. Herein, we report N-doped ordered Pt3Co nanoparticles supported on XC-72R carbon (O-Pt3CoN/C) for oxygen reduction reaction (ORR). Both the X-ray photoelectron spectroscopy and the energy-dispersive X-ray spectroscopy elemental mapping analyses confirm the successful N-doping within the Pt3Co intermetallic compound. Consequently, the N-doped catalyst exhibits a significantly higher ORR performance in comparison with Pt3Co and commercial Pt/C catalysts. Importantly, the ORR mass activity of N-doped Pt3Co intermetallic compound is almost 2.4 times of that obtained on commercial Pt/C. Moreover, after accelerated durability test over the potential range of 0.6 to 1.1 V (vs. RHE), ORR activity decay of N-doped Pt3Co/C is only 21.5%, lower than those of ordered Pt3Co and commercial Pt/C catalysts. Thus, N-doping could be utilized as an effective strategy for further improving the ORR performance of Pt-M/C catalysts.

Catalytic Conversion of Palm Oil to Bio-Hydrogenated Diesel over Novel N-Doped Activated Carbon Supported Pt Nanoparticles

Bio-hydrogenated diesel (BHD), derived from vegetable oil via hydrotreating technology, is a promising alternative transportation fuel to replace nonsustainable petroleum diesel. In this work, a novel Pt-based catalyst supported on N-doped activated carbon prepared from polypyrrole as the nitrogen source (Pt/N-AC) was developed and applied in the palm oil deoxygenation process to produce BHD in a fixed bed reactor system. High conversion rates of triglycerides (conversion of TG > 90%) and high deoxygenation percentage (DeCOx% = 76% and HDO% = 7%) were obtained for the palm oil deoxygenation over Pt/N-AC catalyst at optimised reaction conditions: T = 300 °C, 30 bar of H2, and LHSV = 1.5 h−1. In addition to the excellent performance, the Pt/N-AC catalyst is highly stable in the deoxygenation reaction, as confirmed by the XRD and TEM analyses of the spent sample. The incorporation of N atoms in the carbon structure alters the electronic density of the catalyst, favouring the interaction with electrophilic groups such as carbonyls, and thus boosting the DeCOx route over the HDO pathway. Overall, this work showcases a promising route to produce added value bio-fuels from bio-compounds using advanced N-doped catalysts.

Synthesis of magnetic hollow mesoporous N-doped silica rods as a basic catalyst for the preparation of some spirooxindole-1,4-dihydropyridine derivatives

In this study, magnetic hollow mesoporous N-doped silica rods were successfully prepared via the in-situ calcination of different amounts of diethanolamine in the presence of silica precursor. Doping of the nitrogen atoms in to silica rod structures was performed through a new method and the structure of obtained composite confirmed by X-ray photo electron spectroscopy (XPS), X-ray diffraction (XRD) analysis, elemental analysis, TEM, FESEM and elemental mapping methods. Comparison of the synthesized N-doped catalyst with the same sample without nitrogen atoms (mesoporous silica) showed the high basic characteristic. Furthermore, the efficiency of the prepared basic catalyst was investigated for the synthesis of some spirooxindole-1,4-dihydropyridine derivatives under green conditions. High efficient heterogeneous catalyst, short reaction times (compare with other reported methods) and green conditions are some advantageous of presented method.

Nitrogen-doped ZnWO4 nanophotocatalyst: synthesis, characterization and photodegradation of methylene blue under visible light

Nitrogen-doped ZnWO4 nanoparticles have been synthesized by a sol–gel method using sodium tungstate and zinc acetate in the presence of urea to supply nitrogen. This photocatalyst was characterized by X-Ray diffraction (XRD), field emission-scanning electron microscopy (FESEM), transmission electron microscopy (TEM), an energy dispersive X-ray spectrometer (EDS), the Brunauer–Emmett–Teller technique (BET), photoluminescence (PL) spectroscopy and UV–vis diffuse–reflectance spectrum (DRS). The band gap energy of N-doped ZnWO4 was about 2.99 eV and the absorption wavelength shifted to the visible region in comparison to pure ZnWO4. Also, N-doped catalyst shows enhanced photocatalytic activity for the degradation of methylene blue (MB). The apparent photodegradation rate constant (k) of N-doped ZnWO4 was observed 3.57 × 10−2 min−1 under visible light irradiation.

Enhancement of Light Olefins Selectivity Over N-Doped Fischer-Tropsch Synthesis Catalyst Supported on Activated Carbon Pretreated with KMnO4

Ammonium iron citrate was used as an iron precursor in order to prepare N-doped catalysts supported on KMnO4 pretreated activated carbon (10MnK-AC). Iron nitride was synthesized in company with the formation of α-Fe2O3 on 10MnK-AC. The characterizations of the catalysts show that nitrogen atoms were doped into iron lattice rather than the networks of the carbon support. The performance of Fischer-Tropsch synthesis to light olefins (FTO) suggest an improvement in O/P ratio (olefins to paraffins molar ratio of C2–C4) over the iron catalysts supported on 10MnK-AC. The further promotion of light olefins selectivity (up to 44.7%) was obtained over FeN-10MnK-AC catalyst owing to the collaborative contribution of the electron donor effect of nitrogen and the suppression effect on the second hydrogenation over 10MnK-AC support.

One-Pot Synthesized Pd@N-Doped Graphene: An Efficient Catalyst for Suzuki–Miyaura Couplings

Nitrogen-doped graphene (NDG)-palladium (Pd)-based nanocatalysts (NDG@Pd) can be potentially applied as an efficient catalyst for the preparation of biaryls in a Suzuki–Miyaura coupling reaction. Herein, we report the one-pot facile synthesis of an NDG@Pd nanocatalyst, wherein the nanocatalyst was prepared by the simultaneous reduction of graphene oxide (GRO) and PdCl2 in the presence of hydrazine hydrate as a reducing agent, while ammonium hydroxide was used as a source of “N’’ on the surface of graphene. The as-synthesized NDG@Pd nanocatalyst, consisting of smaller-sized, spherical-shaped palladium nanoparticles (Pd-NPs) on the surface of NDG, was characterized by several spectroscopic and microscopic techniques, including high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET). The nanocatalyst displayed outstanding catalytic activity in the Suzuki–Miyaura cross-coupling reactions of phenyl halides with phenyl boronic acids under facile conditions in water. The catalytic activity of NDG@Pd was found to be a more efficient catalyst when compared to pristine highly reduced graphene oxide (HRG) based Pd nanocatalyst (HRG@Pd). Furthermore, the reusability of the catalyst was also tested by repeatedly performing the same reaction using the recovered catalyst. The N-doped catalyst displayed excellent reusability even after several reactions.

Catalytic performance of dioxide reforming of methane over Co/AC-N catalysts: Effect of nitrogen doping content and calcination temperature

The nitrogen doped activated carbon (AC-N) has been successfully prepared with commercial activated carbon as carbon material followed by a simple N-doping method using melamine as nitrogen sources. Using AC-N as the supports, cobalt supported on N-doped activated carbon (Co/AC-N) were developed and used as catalyst for dry reforming reaction (DRM). It was discovered that the Co/AC-N catalysts revealed much higher catalytic performance for DRM reaction in comparison to activated carbon supported cobalt catalyst (Co/AC). Moreover, the catalytic activity was influenced by preparation conditions of AC-N such as calcination temperature and the doping amount of nitrogen. The catalysts were characterized by BET, XRD, XPS, H2-TPR, Raman spectroscopy and TEM. It was found that catalytic activities of the catalysts with different calcination temperature and nitrogen doping were influenced by catalyst surface defects and disorders, Co2+/Co3+ molar ratio, the content of nitrogen function groups (graphitic N, pyrrolic-N and pyridinic-N) and interaction between active metal and support. The Raman spectroscopy illustrated that the N-doped catalyst surface defects and disorders increased, which improved the performances of the Redox catalysts. The XPS valence band also revealed that higher Co2+/Co3+ molar ratio and nitrogen function groups was achieved by decreasing calcination temperature and increasing nitrogen doping. In short, the doping of nitrogen increased the structural defects and the interaction between active metals and supports, modified the surface electronic structure, which were facilitated the oxidation and reduction of methane and carbon dioxide.

Comparative study on dry reforming of methane over Co-M (M = Ce, Fe, Zr) catalysts supported on N-doped activated carbon

A series of Co-M (M = Ce, Fe, Zr) binary oxides supported on N-doped catalysts were prepared by impregnation methods and tested for DRM reaction. Moreover, the influence of Co and Ce atomic contents in the catalysts on DRM performance was investigated. Significant enhancement of activity performance over Ce promoted 3Co-1Ce/AC-N catalyst was observed. Compared with Fe and Zr, the catalyst with 1/4 mol% of Ce showed the highest activity and was higher than the supported Co catalyst. The calcined and spent catalysts were characterized by XPS, H2-TPR, TEM and EDX mapping studies. The characterization results demonstrated that the increase of 3Co-1Ce/AC-N reforming reactivity was attributed to the presence of Ce in Co-based catalyst, which modified the chemical states of Co-Ce composite oxide and redox properties, and increased the presence of Co2+ species, the content of chemisorbed oxygen and the oxygen mobility. Among the different Co/Ce ratio catalysts, the one with a Co/Ce molar ratio at 1 exhibited better catalytic performance. As the Ce content increases, the content of chemisorbed oxygen was further decreased. In addition, the introduction of N on the support could also affect the catalyst reduction property and interaction of Co-Ce bimetal, which would improve catalytic performance.

In-situ synthesized surface N-doped Pt/TiO2via flame spray pyrolysis with enhanced thermal stability for CO catalytic oxidation

The stability of the heterogeneous catalyst is critical to its working life. To improve the thermal stability of Pt/TiO2, an in-situ surface N-doping process was adopted by introducing a second nozzle above the spray pyrolysis flame, and in which method a high-temperature resistant catalyst was prepared and applied to the catalytic oxidation of CO. Moreover, the structure morphology, carrier phase composition, surface structure and species of the catalyst, the valence state of the loaded Pt particles and the surface element types were analyzed, which indicate that the nitrogen atoms are mainly present on the surface of the catalyst with interstitial doping in Ti–O–N and/or Ti–N–O structure. Besides, after calcination at 300 °C, 400 °C, 500 °C, and 600 °C, respectively, the particle size of these two catalysts and the phase transition of the TiO2 carrier were investigated. The results show that the N-doped Pt/TiO2 exhibited better stability, and its complete CO conversion temperature was controlled within 10 °C at 500 °C (∆T100 = 10 °C), which is more stable than 70 °C reduction of the pure Pt/TiO2 (∆T100 = 70 °C). This N-doped catalyst exhibits superior thermal stability in general, which is attributed to the formation of the stronger PtN bonds, resulting in a better resistance to sintering and a little phase transition during the calcination process.

Simple synthesis of N-doped catalysts with controllable Pt–Ni nanoparticles for high-efficiency ethanol oxidation

Herein, the catalysts contained metal- and nitrogen-doped carriers were synthesized by a novel and simple method. The synthesized catalysts with different particle size and distribution were controlled by adjusting the ratio of urea and metal salt solution. The morphology, microstructure, and particle distribution of the catalysts were confirmed by transmission electron microscopy and X-ray powder diffraction. The catalytic performance of the catalysts was tested by cyclic voltammetry (CV) and amperometric i-t curves. It was found that the urea content had an influence on the distribution of metal particles and the size of the nanoparticles. More catalyst active sites were formed on the surface of the catalyst due to that many nitrogen-based functional groups were formed on the surface of the carrier. Compared with other samples, catalyst with urea amount of 100 mg (Pt2Ni3/C–N3 samples) possessed small particle size and uniform distribution, which exhibited higher electrocatalytic activity and stability, and the maximum of forward anodic peak reached 1454 mA mg−1.

Catalytic Dehydrochlorination of 1,2-Dichloroethane into Vinyl Chloride over Nitrogen-Doped Activated Carbon.

The pyrolysis of 1,2-dichloroethane (EDC) is the most popular commercialized way of producing vinyl chloride monomers (VCM); however, it is plagued by high-energy consumption and the resulting coke formation. Here, a series of nitrogen-doped (N-doped) activated carbon catalysts (N-AC) were prepared conveniently for EDC dehydrochlorination. The structural and textural properties of N-doped catalysts were characterized by X-ray diffraction, transmission electron microscopy, Raman spectra, temperature-programmed desorption of VCM and EDC, and X-ray photoelectron spectroscopy. The results revealed that doping N into activated carbon supports introduced basicity sites and caused partial graphitization on the catalyst surfaces. Thus, an improved absorption capacity to EDC and VCM and an accelerated desorption rate were obtained, which greatly enhanced EDC conversion and VCM selectivity. EDC was almost completely dehydrochlorided into vinyl chloride at a temperature of 300 °C and an EDC liquid hourly space velocity of 0.313 h–1. The high catalytic activity and selectivity as well as good stability suggested that the N-AC catalyst would be a promising dehydrochlorination catalyst on an industrial scale.

Catalytic performance of N-doped activated carbon supported cobalt catalyst for carbon dioxide reforming of methane to synthesis gas

Abstract Activated carbon (AC) was treated with melamine to prepare nitrogen-doped carbon materials (AC-N), which used as support to prepare Co supported catalysts for CH4–CO2 reforming (DRM) reaction and its catalytic performance was investigated. The modified (Co/AC-N) and unmodified (Co/AC) catalyst were characterized by BET, H2-TPR, XRD, TEM, XPS, CO2-TPD and FTIR. It was found that the modified catalyst not only showed excellent stability, but also had better catalytic activity than the unmodified catalyst. Although the physical structure of modified catalysts is almost same with the unmodified catalysts, nitrogen and some oxygen functional groups such as pyridine nitrogen, pyrrole nitrogen, hydroxyl and oxygen incarbonyl groups were generated on the AC surface during the amination treatment. The generated surface nitrogen and oxygen functional groups affect not only influence the dispersion of active metals but affect the valence distributions of cobalt. Compared with the untreated catalyst, small active particle size with a narrow size distribution formed on the surface of N-doped catalyst. Moreover, the modified catalyst also provides more basic sites for the reforming reaction to accelerate the adsorption and dissociation of CO2 on the active site of the catalyst.

Nitrogen doped tin oxide nanostructured catalysts for selective electrochemical reduction of carbon dioxide to formate

Tin/tin oxide materials are key electrocatalysts for selective conversion of CO2 to formate/formic acid. Herein we report a tin oxide material with nitrogen doping by using ammonia treatment at elevated temperature. The N doped material demonstrated enhanced electrocatalytic CO2 reduction activity, showing high Faradaic efficiency (90%) for formate at –0.65 V vs. RHE with partial current density of 4 mA/cm2. The catalysis was contributed to increased electron negativity of N atom compared to O atom. Additionally, the N-doped catalyst demonstrates sulfur tolerance with retained formate selectivity. The analysis after electrolysis shows that the catalyst structure partially converts to metallic Sn, and thus the combined Sn/N–SnO2 is the key for the active CO2 catalysis.

Synergistic effect of nitrogen-doped carbon-nanotube-supported Cu–Fe catalyst for the synthesis of higher alcohols from syngas

Heteroatom doping is an attractive approach for improving the properties of carbon materials for various applications. In this study, a series of nitrogen-doped (N-doped) carbon-nanotube-supported Cu–Fe (xCun–Fem/yN-CNT) catalysts were prepared for CO hydrogenation to higher alcohols. The structural and textural properties of N-doped catalysts were characterized by X-ray diffraction, transmission electron microscopy, hydrogen temperature-programmed reduction, and CO2 temperature-programmed desorption. The results revealed that doping N into CNT supports improved the Cu–Fe dispersion, strengthened the interaction of Cu and Fe species with N-CNT, and introduced many surface-basicity sites. Thus, an improved CO conversion and excellent selectivity to higher alcohols [S(C2+–OH)] were obtained. Furthermore, the selectivity to alcohols [S(ROH)] and S(C2+–OH)/S(MeOH) over the optimized 15Cu1–Fe1/1.3N-CNT catalyst reached 27.2% and 2.2, while the corresponding values were 20.2% and 0.4, respectively, over the catalyst without N doping under identical reaction conditions. The present results on N-CNT supported Cu–Fe catalyst will provide further understanding on the catalyst design for the transformation of syngas to higher alcohols.

Coexistence of sulfonic and pyridinic sites on H2SO4 treated N-doped carbon nanotubes

Three types of purified nitrogen doped CNTs were tested for isopropyl alcohol conversion under nitrogen or air atmosphere, and compared to undoped CNTs. The N-doped CNTs differ from their nitrogen content, from the presence or not of undoped section in their structure, and from their sulfur content. The isopropyl alcohol conversion leads to the formation of acetone as the sole product on catalysts presenting no nitrogen or low nitrogen and sulfur content, pointing to the presence of basic sites. At higher nitrogen and sulfur content, N-doped catalysts lead to the formation of acetone and propene, highlighting the presence of both basic and acidic sites on such material. XPS characterizations allow us to propose that the basic sites consist in pyridinic surface groups, and the acidic sites in sulfonic surface groups formed during the purification of these materials with sulfuric acid.

Mesoporous carbon doped with N,S heteroatoms prepared by one-pot auto-assembly of molecular precursor for electrocatalytic hydrogen peroxide synthesis

A bottom-up approach based on hydrothermal carbonization of organic molecules has been used to prepare carbon materials doped with either nitrogen or sulfur or both. To generate mesopores, ZnCl2 has been used as removable structure-directing agent. The final mean mesopore size depended on the type of dopant element. The doped materials exhibited remarkable activity as electrocatalyst in oxygen reduction reaction with nearly complete selectivity to H2O2 synthesis. Two pyrolysis temperatures (973K and 1173K) were used that yield materials with different electric conductivity, dopant content and porosity but comparable electrocatalytic performance. N-doped catalyst with an intermediate nitrogen content (4wt%) and around 80% of pore volume in the mesopore range provided the best performance among the catalysts tested.

Catalytic wet oxidation of organic compounds over N-doped carbon nanotubes in batch and continuous operation

Multi-walled carbon nanotubes (MWCNTs) were treated by ball milling with and without a nitrogen precursor (melamine) to introduce nitrogen functionalities. These materials were tested as catalysts in batch and continuous catalytic wet oxidation (CWO) experiments for the degradation of phenol in aqueous solution. The influence of several reaction parameters (temperature, dissolved oxygen concentration and initial phenol concentration) were studied in both operating modes. Temperature had a more significant effect on the reaction rate than the dissolved oxygen concentration, an optimal temperature of 160°C being determined. The experiments with different initial phenol concentrations showed that higher amounts of phenol and carbon contents were removed when the initial concentration of phenol was increased. MWCNTs with N-groups showed high catalytic activity for phenol removal in both operation modes, as also observed when performing some experiments with oxalic acid. For instance, complete phenol degradation and 50% of total organic carbon (TOC) removal were achieved after 2h in batch operation at 160°C and 6bar of oxygen partial pressure with the N-doped catalyst (against 68% and 50%, respectively, with the undoped sample). In the continuous mode reactor, 80% and 50% of phenol and TOC removals were observed at the steady state with the N-doped catalyst, in this case at 160°C and 12bar of oxygen partial pressure with an initial phenol concentration of 500mgL−1. A significant regeneration of the N-doped catalyst was achieved by thermal treatment at 600°C under nitrogen atmosphere.