N-doped Catalysts Research Articles

Chitosan pyrolysis in the presence of a ZnCl2/NaCl salts for carbons with electrocatalytic activity in oxygen reduction reaction in alkaline solutions.

The one-step carbonization of low cost and abundant chitosan biopolymer in the presence of salt eutectics ZnCl2/NaCl results in nitrogen-doped carbon nanostructures(8.5 wt.% total nitrogen content). NaCl yields the spacious 3D structure, which allows external oxygen to easily reach the active sites for the oxygen reductionreaction (ORR) distinguished by their high onset potential and the maximum turnover frequency of 0.132 e site⁻1s⁻1. Data show that the presence of NaCl during the synthesis exhibits the formation of pores having large specific volumes and surface(specific surface area of 1217 m2g-1), and holds advantage by their pores characteristics such as their micro-size part, which provides a platform for mass transport distribution in three-dimensional N-doped catalysts for ORR. It holds benefit over sample pre-treated with LiCl in terms of the micropores specific volume and area, seen as their percentage rate, measured in the BET. Therefore, the average concentration of the active site on the surface is larger.

Which Insights Can Gas Diffusion Electrode Half-Cell Experiments Give into Activity Trends and Transport Phenomena of Membrane Electrode Assemblies?

In order to push the energy turnaround forward, research and development on technologies enabling storage and release of renewable energies, such as water electrolysis and fuel cells is vital in the current decade. For both processes it is essential to collect meaningful data for catalyst activity in terms of transferability to the industrial application already on the lab-scale and at an early stage of material development. Gas diffusion electrode (GDE) half-cell setups were recently presented as a fast and cost-effective tool to characterize oxygen reduction reaction (ORR) catalyst layers at fuel cell relevant potentials and current densities (3 A cm-2) [1]. An Inter-lab comparison demonstrated that GDE testing with various, slightly differing setups can deliver data that is both reliable and comparable if standardized measurement protocols are followed [2]. On the way to widespread application, it is essential to evaluate to which extend GDE half-cell measurements can provide reasonable trends of how catalyst layer properties influence ORR activity in membrane electrode assembly (MEA) applications, despite the major influence of the active metal itself. Elucidating possibilities and limitations of GDE half-cell measurements to study catalyst layer influences is scope of this study.The transferability of trends was studied for i) an ionic liquid modified and unmodified Pt/C catalyst (following our previous work [3]) and ii) employing nitrogen modified carbon support at different ionomer to carbon ratios (following the work of Ott et al. [4]). Regarding the activity increase due to IL modification we will show that rotating disk electrode (RDE) and GDE results at low current densities show the same trend. GDE testing also shows a maximum activity depending on the IL loading at slightly elevated current densities. In the high current density regime, however, MEA testing showed a negative effect of the IL modification, which was also obtained correctly within the GDE testing at the same current densities. For the N-doped Pt/C catalyst a positive effect was observed in MEA characterization with low ionomer content under dry conditions, where proton transport losses are dominant for the unmodified catalyst. However, at higher I/C ratio and under wet conditions, where proton transport is sufficient for both unmodified and N-doped catalyst, worse performance after N modification is observed in the high current density regime. During GDE evaluation only the latter phenomenon could be capture and the unmodified catalyst showed a superior performance over the N-doped material at any I/C ratio in the ohmic and in the mass transport limiting regime.In summary, we showed that GDE half-cell experiments, where the catalyst layer is in direct contact with the liquid electrolyte, can be used to reliably predict trends in catalytic activity for real MEAs at high current densities that are related to differences in oxygen mass transport [5]. However, differences in catalytic activity being related to proton accessibility especially at lower relative humidities cannot be captured completely, as the catalyst layer is always wetted fully. An introduction of an ionomer membrane between catalyst layer and liquid electrolyte might be necessary during GDE evaluation for a reliable description of all transport phenomena in real fuel cells. Nevertheless, our results indicate that GDE measurements without the utilization of an ionomer membrane allow for the study of oxygen mass transport properties independent of other transport phenomena at fuel cell relevant current densities.Literature:[1] Schmitt et al. Electrochemistry Communications 2022, 141, 107362 [2] Ehelebe et al. ACS Energy Lett. 2022, 7, 816-826. [3] Zhang et al. Advanced Functional Materials 31.28 (2021): 2010977 [4] Ott et al. Nature materials 19.1 (2020): 77-85. [5] Schmitt et al. Energy Adv. 2023, 2, 854.

N-doped MOF-lignin hybrid catalyst for highly selective hydrodeoxygenation of lignin-derived phenols

Upgrading of lignin-derived bio-oil to value-added biofuel was of great significance for efficient utilization of renewable resources and reducing the use of fossil fuels. Hydrodeoxygenation (HDO) was considered to be a promising technology for the conversion of lignin-derived bio-oil. Herein, we reported a novel method for the preparation of lignin-MOF derived N-doped catalysts, which was then successfully introduced into the upgrading of lignin-derived phenols and lignin depolymerization. All catalysts were well characterized and Co/CN-0.5–750 exhibited excellent performance during the catalytic HDO process. The optimized catalyst demonstrated highly efficient active hydrogen generation from isopropanol. Moreover, it could afford the best vanillin (VAN) conversion (100 %) and highest 2-Methoxy-4-methylphenol (MMP) yield (92 %) under the mild reaction conditions (180 °C, 0.5 MPa nitrogen, 2 h). It was confirmed that the excellent performance was related to nitrogen doping. This study could provide some useful insights for the hydrodeoxygenation of lignin and its derivative.

Nitrogen species from Spirulina platensis derived bio-oil enhance catalytic activity of cobalt catalysts for hydrogenation

High nitrogen content in Spirulina platensis-derived bio-oil is a highly undesirable feature in upgrading of bio-oil to biofuel via hydrodeoxygenation. However, the nitrogen species could be potentially used as dopant for tailoring the catalytic behaviors of metallic sites in heterogeneous catalysts. In this study, the nitrogen species in the bio-oil from hydrothermal carbonization (HTC) of Spirulina platensis was used to modify Co-based catalyst for enhancing their catalytic activity for hydrogenation of o-chloronitrobenzene (o-CNB). The results showed that the introduction of N species not only promoted dispersion of Co particles via formation of Co–N sites, but also generated extra pores and significantly increased H2 uptake. The abundant Co–N sites, high dispersion of Co and higher surface area of N-doped catalyst (CoFeAl–N) jointly contributed to the enhanced catalytic activity for hydrogenation of o-CNB, achieving the yield of 90.3% for o-chloroaniline (o-CA) and lowering the activation energy from 63.0 kJ mol−1 (with N-free CoFeAl catalyst) to 55.1 kJ mol−1. The effectiveness of introducing nitrogen for enhancing catalytic activity for hydrogenation of o-CNB was also confirmed in the experiments for doping Co/Al2O3 (prepared via impregnation) and CoAl (prepared via co-precipitation) catalysts with the Spirulina platensis derived bio-oil.

Sonocatalytic Activity of Porous Carbonaceous Materials for the Selective Oxidation of 4-Hydroxy-3,5-dimethoxybenzyl Alcohol.

Selective oxidation, which is crucial in diverse chemical industries, transforms harmful chemicals into valuable compounds. Heterogeneous sonocatalysis, an emerging sustainable approach, urges in-depth exploration. In this work, we investigated N-doped or non-doped carbonaceous materials as alternatives to scarce, economically sensitive metal-based catalysts. Having synthesized diverse carbons using a hard-template technique, we subjected them to sonication at frequencies of 22, 100, 500, and 800 kHz with a 50% amplitude. Sonochemical reaction catalytic tests considerably increased the catalytic activity of C-meso (non-doped mesoporous carbon material). The scavenger test showed a radical formation when this catalyst was used. N-doped carbons did not show adequate and consistent sonoactivity for the selective oxidation of 4-Hydroxy-3,5 dimethoxybenzyl alcohol in comparison with control conditions without sonication, which might be associated with an acid-base interaction between the catalysts and the substrate and sonoactivity prohibition by piridinic nitrogen in N-doped catalysts.

Developing and understanding Leaching-Resistant cobalt nanoparticles via N/P incorporation for liquid phase hydroformylation

The ultimate target in heterogeneous catalysis is the achievement of robust, resilient and highly efficient materials capable of resisting industrial reaction conditions. Pursuing that goal in liquid-phase hydroformylation poses a unique challenge due to carbon monoxide-induced metal carbonyl species formation, which is directly related to the formation of active homogeneous catalysts by metal leaching. Herein, supported heteroatom-incorporated (P and N) Co nanoparticles were developed to enhance the resistance compared with bare Co nanoparticles. The samples underwent characterization using operando XPS, XAS and HR electron microscopy. Overall, P- and N-doped catalysts increased reusability and suppressed leaching. Among the studied catalysts, the one with N as a dopant, CoNx@NC, presents excellent catalytic results for a Co-based catalyst, with a 94% conversion and a selectivity to aldehydes of 80% in only 7.5 h. Even under milder conditions, this catalyst outperformed existing benchmarks in Turnover Numbers (TON) and productivity. In addition, computational simulations provided atomistic insights, shedding light on the remarkable resistance of small Co clusters interacting with N-doped carbon patches.

N-doped catalysts built by iron-based metal–organic framework efficiently activated peroxymonosulfate for the tetracycline degradation

Tetracycline, one of the most commonly used antibiotics, has emerged as a critical concern in water pollution treatment. N-doped iron-based catalysts were prepared by one-step pyrolysis with MIL-101 (Fe) as precursors in this study. The effects of doping ratio, material dosage, anions and other factors on the degradation efficiency of tetracycline were investigated. In best conditions, the removal rate of tetracycline has reached 91%, which was attributed to the synergistic effect of free radical (i.e., SO4•−, •OH) and non free radical pathways (i.e., 1O2). And the ion leaching of N doped catalysts was investigated. The iron ion leaching was maintained at a relatively low level. Then, LC-MS was used to study the pathway of tetracycline degradation. ECOSAR assessments had demonstrated that tetracycline and its intermediates exhibited significantly reduced levels of acute toxicity, developmental toxicity, and mutagenicity. These studies indicated that the derivative of N-doped iron-based MOFs was a highly promising, environmentally friendly catalyst for practical wastewater treatment applications.

Electrocatalytic activity analysis of vinegar residue-based heteroatom-doped carbon quantum dots integrated on vertically aligned graphene arrays for hydrogen evolution reaction

Carbon-based materials are considered cost-effective electrocatalysts for hydrogen evolution reaction (HER). Here we design the heteroatom-doped carbon quantum dots (CQDs) loaded on vertical graphene (VG) as HER catalyst by density functional theory (DFT). And heteroatoms (B/N/P/S)-doped CQDs is synthesized with vinegar residue as the carbon source, which are integrated on VG as HER electrocatalysts. The results of electrochemical measurements are consistent with the DFT calculations. The heteroatom of CQDs in heteroatom-doped CQDs loaded on VG (CQDs-VG) is the leading active site in the HER process, which increases the catalytic potential of VG. The VG substrate increases the electron density of the heteroatom, which decreases the energy barrier and improves the catalytic activity. The N-doped catalyst shows the best potential in the HER process. This work contributes for the development of carbon based cost-effective electrocatalysts for water-splitting.

The effect of nitrogen doping on hydrogenation capability and stability of Cu-based catalyst in ester hydrogenation to methyl glycolate

Methyl glycolate (MG) was a significant chemical raw material of biodegradable and bioabsorbable polyglycolic acid (PGA). In this work, the N-doped layered carbon supported Cu catalysts were constructed for dimethyl oxalate (DMO) hydrogenation to MG. Nitrogen doping had significant effects on the particle size, valence state and electronic environment of Cu species. The electronic interaction between Cu species and N-doped carbon support improved the Cu0/(Cu0 + Cu+) ratio and electron density surrounding Cu species in N-doped catalysts. The synergistic effect of high Cu0/(Cu0 + Cu+) ratio and electron density made Cu species in Cu/C-E catalyst showed up to 74.84% MG yield. More importantly, the intimate interaction between Cu species and N-doped carbon support improved the thermal and valence stability of Cu catalyst, resulting in the Cu/C-E catalyst with a much higher stability of over 600 h than the currently reported Cu catalyst.

Engineering of the N-doped carbon support for improved performance of supported Pd catalysts in hydrogen production from gas-phase formic acid

Development of N-doped Pd/C catalysts for hydrogen production from gas-phase formic acid is a challenge. To elucidate the efficient routes of nitrogen insertion on the surface of a mesoporous carbon support, the latter was treated with melamine (Mel), dicyandiamide or NH3 at 673 and 823 K. Pyrolysis of the melamine/carbon mixture taken in a 1:2 ratio provides an increase in the reaction rate by a factor of 5. The inserted N-sites strongly interact with Pd leading to the formation of highly dispersed Pd nanoparticles (∼1.6 nm) and active atomically dispersed Pd2+ species. With a further increase of the Mel/C ratio, the number of surface N-sites decreases due to occupation of carbon support pores with a g–C3N4–type residue. This provides a decrease in the Pd dispersion leading to lower reaction rates. Therefore, melamine is an efficient N precursor. The considered synthesis of N-doped catalysts could be scaled.

Highly Dispersed Ni on Nitrogen-Doped Carbon for Stable and Selective Hydrogen Generation from Gaseous Formic Acid.

Ni supported on N-doped carbon is rarely studied in traditional catalytic reactions. To fill this gap, we compared the structure of 1 and 6 wt% Ni species on porous N-free and N-doped carbon and their efficiency in hydrogen generation from gaseous formic acid. On the N-free carbon support, Ni formed nanoparticles with a mean size of 3.2 nm. N-doped carbon support contained Ni single-atoms stabilized by four pyridinic N atoms (N4-site) and sub-nanosized Ni clusters. Density functional theory calculations confirmed the clustering of Ni when the N4-sites were fully occupied. Kinetic studies revealed the same specific Ni mass-based reaction rate for single-atoms and clusters. The N-doped catalyst with 6 wt% of Ni showed higher selectivity in hydrogen production and did not lose activity as compared to the N-free 6 wt% Ni catalyst. The presented results can be used to develop stable Ni catalysts supported on N-doped carbon for various reactions.

N-doped activated carbon as support of Pd-Sn bimetallic catalysts for nitrate catalytic reduction

This work studies the catalytic reduction of nitrate using N-doped activated carbon catalysts. Activated carbons were prepared by hydrothermal carbonization (220 °C, 80 % water, 16 h) of garden and park waste and olive stones using (NH4)2SO4 as N source, followed by chemical activation with H3PO4 at 500 °C (N2 atmosphere, 1 h). These were impregnated with Pd and Sn to prepare bimetallic catalysts for nitrate catalytic reduction. N-doping improved the BET surface area up to 1369 m2 g−1 and increased the N content on the catalyst surface to 3 wt%. The N-doped catalysts showed better catalytic performance than the non-doped ones, showing high stability for 100 h on stream, reaching even higher activity than a catalyst supported on a commercial activated carbon. N-doping also showed a positive effect by decreasing NH4+ selectivity. Finally, natural and drinking waters spiked with NO3- were treated in continuous flow, exhibiting the N-doped activated carbon catalysts, prepared from garden and park waste, a high tolerance to ions other than NO3- present in the water solution.

Advantageous Role of N-doping on K@Al in COS/CS2 Hydrolysis: Diminished Oxygen Mobility and Rich basic sites

Basic sites are important to promote carbonyl sulfide (COS) and carbon disulfide (CS2) hydrolysis activity while improving the oxidation resistance of hydrolysis catalysts is a challenge. Here, we report an N-doped alumina-based catalyst (N-K@Al), where the complete hydrolysis removal of COS and CS2 by the N-doped catalyst was extended up to 15 h at 160 °C, and the turnover frequency (TOF) value of the catalyst was increased from 0.85 × 10-2 s−1 to 1.16 × 10-2 s−1. The results showed that the strong interaction between nitrogen and potassium decreased the reactive oxygen density and activated –OH, weakening the oxygen mobility. In addition, the beneficial effects of N-doped included the addition of moderately and weakly basic sites by pyridine N. The optimized N-K@Al showed good catalytic performance in the hydrolysis of COS and CS2 removal with lower reaction temperature and higher total hydrogen sulfide yield. Density functional theory calculations revealed that N-K@Al reduced the Gibbs free energy of COS and CS2 hydrolysis to 0.21 eV and 0.33 eV, respectively, contributing to the enhanced catalytic activity. The present study presents new strategies for developing efficient antioxidant organosulfur hydrolyzers and other practical industries.

N-doped carbon nanosheets derived from lignin as a novel bifunctional electrocatalyst for rechargeable zinc-air battery

New energy utilization devices have attracted great research interest as a sustainable route for clean energy production. However, the disadvantage of this process is the need to use high-cost precious metal catalysts. Hereby, N-doped carbon nanosheets (LNZ@GC) was prepared by ball milling-carbonization two step strategy using alkali lignin as carbon source and the gas-phase exfoliation with NH4Cl and ZnCl2 as pore-forming agents. We investigative the properties of LNZ@GC series and find that LNZ@GC exhibit the most excellent ORR performances with a half-wave potential up to 0.851 V, outstanding stability and methanol tolerance, which are all superior commercial Pt/C. Furthermore, the rechargeable zinc-air battery assembled by LNZ-800@GC shows excellent performance with a high power density of 841.8 Wh kg−1, a large specific capacity of 750.3 mA h g−1. This work not only provides a general strategy for the preparation of porous N-doped catalysts, but also provides technical support for the design and development of inexpensive catalysts using lignin as a carbon source.

Facile synthesis of N-doped TiO2 and its photocatalytic properties for ciprofloxacin degradation

The preparation of N-doped TiO2 with excellent photocatalytic performance is reported. The study of the synthesis process involves the control of N-doping and the crystalline phase. The incorporation of urea provides dual features; it introduces a nitrogen source and also reduces the phase transition temperature of anatase to rutile. The optimal N-doped catalyst that possesses both anatase and rutile phases shows excellent catalytic efficiency in the degradation of ciprofloxacin under illumination by visible light and sunlight.

The investigation of the role of nitrogen in the improvement of catalytic activity and stability of Zr/Ti-based material for carbon disulfide hydrolysis

A nonmetallic N-doped Zr/Ti-based catalyst was prepared to investigate the effect of N addition on catalytic performance for carbon disulfide (CS2) hydrolysis. The characterization of the catalyst indicated that doped N atoms were present as interstitial N in the TiO2 lattice, resulting in an increase in the number of basic sites of the catalyst from 1.64 to 2.37 and from 0.68 to 2.53 for weakly basic and strongly basic sites, respectively. In addition, the doping of N promoted the formation of OH groups, which were favorable for the hydrolysis of CS2, from water (H2O) adsorbed on the catalyst, thus greatly improving the performance of catalytic CS2 hydrolysis. However, N doping reduced the amount of chemisorbed oxygen on the catalyst surface from 44.7% to 33.4%, thus decreasing the oxidation reaction of the hydrolysis product H2S and improving the stability of the catalyst. CS2 hydrolysis reaction activity and catalyst lifetime were tested. The experimental results demonstrated that the catalytic CS2 hydrolysis performance was greatly improved after N doping, and the temperature to obtain 100% conversion was reduced from 180 °C to 130 °C. Selectivity to H2S was greatly improved with N-doped catalysts. Furthermore, the resistance of the catalyst to sulfate was improved. Nonmetallic N-doped Zr/Ti-based catalysts offer a new strategy for blast furnace gas desulfurization.

Effect of N-doping and carbon nanostructures on NiCu particles for hydrogen production from formic acid

A series of NiCu based catalysts were prepared using different carbon nanostructure as support and loading 2.5 wt% of each metal. The studied nanocarbon materials were: reduced graphene oxide (rGO), N-doped reduced graphene oxide (NrGO), high surface area graphite (HSAG), single and multiwalled carbon nanotubes (SWCNT and MWCNT), N-doped carbon nanotubes (NCNT), spheres of xerogel carbons (SXC) and N-doped SXC (NSXC). The effect of N-doping, electronic properties and morphology of the carbon nanostructures on the metallic particle size was studied as well as their capacity to produce high purity hydrogen from formic acid decomposition at low temperature. The NiCu based catalysts tested are highly selective to H2 (98−94 % at conversions above 95 %). The site time yield (STY) of the catalysts follows the order: NCNT > SXC > SWCNT∼HSAG∼rGO10>rGO325>MWCNT∼NSXC > NrGO325>NrGO10, indicating that N-doped catalysts are less active, except in the case of NCNT which is ascribed to the N-pyrrolic heteroatoms of this material.

(Invited) N-Doped Carbon-Based Materials: Improved Fundamental Understanding through Comprehensive Characterization

N-doped carbon materials are used across a wide range of energy applications including fuel cell catalysts, CO2 electroreduction, catalyst supports, and energy storage materials. They are often integrated with metals in the form of either metal nanoparticles or atomically-dispersed sites to tune their performance for specific catalytic reactions. In general, these materials are very heterogeneous, containing a multitude of nitrogen functionalities and therefore, they are intrinsically challenging to understand, requiring a wide range of characterization techniques.This talk will discuss a family of N-doped catalysts derived from a series of N-doped carbon nanospheres. N-doped nanospheres, produced solvothermally, are synthesized with the ability to control size, shape, concentration of nitrogen dopants, and their nitrogen functionalities. The tunability of these spheres allows for systematic studies that help to identify trends with different N functionalities and densities. Platinum and non-platinum metals were incorporated using various synthetic routes, targeting formation of either metal nanoparticles or atomically-dispersed species. Understanding the surface and bulk chemistry of these materials is essential for elucidating the effects of nitrogen dopants on nucleation and stability of metals across the periodic table. Trends observed experimentally will be compared with metal adsorption computations with the goal of extending beyond experimental data to make predictions for more efficient catalyst development. Within a catalyst layer, the surface chemistry also affects interactions with ionomer, and both the nature of the metal and its morphology, as well as the functionality of nitrogen impacts these interactions.

Recycling of waste tires by synthesizing N-doped carbon-based catalysts for oxygen reduction reaction

Currently, there are 1.5 billion waste tires (WTs) produced yearly, which has become a vital issue worldwide. In this study, we suggest to recycle rubbers and carbon black (CB) together by carbonizing rubbers in WTs. Sulfonation of WT rendered stable structure to carbonize rubbers, which are innately non-carbonizable. The following heat-treatment in Ar/NH3 atmosphere provided abundant nitrogen functional groups on resulting carbons including CB and carbonized rubbers, confirmed by X-ray photoelectric (XPS) spectroscopy and TEM micrographs. To validate them as oxygen reduction reaction (ORR) catalysts, a half-cell test in alkaline media was carried out. The N-doped catalyst with carbonized rubbers and CB exhibited a superior ORR activity to that with carbonized WTs without sulfonation and further those performance was comparable to a Pt/C catalyst. It is evident that carbonized rubbers induced higher nitrogen contents and larger electrochemical surface areas of the catalyst, which offered more active sites higher ORR activity. Therefore, we believed that the proposed approach introduced in this paper shows an effective solution to deal with WTs by envisioning alternative recycling pathway.

Ferrocene-crosslinked polypyrrole hydrogel derived Fe–N-doped hierarchical porous carbon as an efficient electrocatalyst for pH universal ORR and Zn–air batteries

A Fe–N-doped catalyst (PF-800), prepared via pyrolysis of ferrocene-crosslinked polypyrrole hydrogel, shows impressive activity for ORR in various pH. Further Zn–air battery using PF-800 present high energy density and excellent long-term stability.