Non-metal Catalysts Research Articles

Unexpected Intrinsic Catalytic Function of Porous Boron Nitride Nanorods for Highly Efficient Peroxymonosulfate Activation in Water Treatment.

Porous boron nitride (BN) nanorods, which were synthesized via a one-stage pyrolysis, exhibited excellent catalytic performance for organics' degradation via peroxymonosulfate (PMS) activation. The origin of the unexpected catalytic function of porous BN nanorods was proposed, in which non-radical oxidation driven by the defects on porous BN dominated the sulfamethoxazole degradation via the generation of singlet oxygen (1O2). The adsorption energy between PMS and BN was calculated via density functional theory (DFT), and the PMS activation kinetics were further investigated using an electrochemical methodology. The evolution of 1O2 was verified by electron spin resonance (ESR) and chemical scavenging experiments. The observed non-radical oxidation presented a high robustness in different water matrices, combined with a series of much less toxic intermediates. The used BN was easily regenerated by heating in air, in which the B-O bond was fully recovered. These findings provide new insights for BN as a non-metal catalyst for organics' degradation via PMS activation, in both theoretical and practical prospects.

A silk-like hydrogen-bonded organic framework functionalized membrane with intrinsic catalytic activity for nonmetallic reduction of 4-nitrophenol

Investigating the hydrogen-bonded organic frameworks (HOFs) with intrinsic functions has been a great challenge for the development of HOF materials. In this paper, an efficient way of obtaining a HOF with intrinsic catalytic activity is presented. A microporous HOF-PyTTA was self-assembled by using 4,4′,4′',4′''-(pyrene-1,3,6,8-tetrayl) tetraaniline (PyTTA) as an organic monomer. The monomer has a pyrene ring with a conjugated structure, which is conducive to the construction of large-area π-π interactions, therefore improving the stability of the HOF structure. The amino-functional group of the monomer serves as the active site which enables the HOF-PyTTA, which acts as a non-metallic catalyst to catalyze the conversion of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The permanent pore structure of the HOF-PyTTA was confirmed by X-ray single-crystal diffraction and CO2 isotherm adsorption experiments. To broaden the application of HOF-PyTTA, we propose growing HOF-PyTTA on the filter membranes of diverse materials and making a catalytic column by filling the HOF-PyTTA/glass fiber membrane into the syringe. After pouring the mixture of 4-NP and NaBH4 into the catalytic column, 4-NP was converted into 4-AP with a high rate of conversion. This work develops a simple, robust, and flexible HOF with intrinsic catalytic reduction activity for 4-NP, and broadens the application of HOF for functional modification and catalytic application.

Direct Phosphonylation of N-Phenyltetrahydroisoquinolines in Microdroplets.

Because of their unique properties and high biological activities, organophosphorus compounds have been used worldwide in agricultural, industrial, medicinal, and veterinary applications. Conventional strategies for direct phosphonylation suffer from the usage of stoichiometric or excessive metallic or nonmetallic catalysts and long reaction times under harsh conditions, leading to a strong desire for environment-friendly protocols for phosphonylation. A protocol for the accelerated phosphonylation of N-phenyltetrahydroisoquinolines in minutes was developed without the use of any catalyst in microdroplets. The phosphonylation process was completed (>85% yields) in 10 min at 40 °C using 0.8 equiv 2,3-dicyano-5,6-dichlorobenzoquinone as the oxidant and acetonitrile as the solvent. The microdroplet phosphonylation strategy showed good suitability to alkyl phosphites and N-phenyltetrahydroisoquinolines bearing electron-withdrawing and electron-donating substitutes, and the yields of the microdroplet reaction were much greater than those of the bulk (accelerated by two orders of magnitude from the ratio of the rate constants using the microdroplet and the bulk method). Furthermore, microdroplet phosphonylation can be scaled up to a 1-phenyl-2-dimethylphosphonite-1,2,3,4-tetrahydroisoquinoline amount of 510 mg h-1 by spraying 0.1 mol L-1 N-phenyltetrahydroisoquinoline at 300 μL min-1. These figures of merit make it a promising alternative to classic organic methodologies for the synthesis of organophosphorus compounds.

Polymeric ionic liquid with carboxyl anchored on mesoporous silica for efficient fixation of carbon dioxide

The utilization of carbon dioxide (CO2) has drawn much attention because of the increasing serious environmental problems. In order to promote the cycloaddition reaction of CO2 to epoxides, a new synthesis strategy for friendly nonmetal catalyst to combine polymeric ionic liquid (PIL) with mesoporous silica (mSiO2) was proposed. By thorough characterizations, those catalysts (mSiO2-PIL-n, n = 1, 2, 3, 4) were verified that PIL with multiply catalytic active sites such as carboxyl group, imidazole ring and Br–, was mainly anchored in mesoporous SiO2 structures. Therefore, mSiO2-PIL-n exhibited excellent catalytic activity for CO2 cycloaddition reaction to epoxides under solventless and cocatalyst-free conditions. Typically, the appropriate PIL loading and specific surface area guaranteed mSiO2-PIL-2 could efficiently catalyze the cycloaddition reaction with 96% yield and 99% selectivity to the target product of propylene carbonate under the conditions of 120 °C, 2 MPa and 6 h. Additionally, the mSiO2-PIL-2 catalyst showed superior recyclability and there was no catalytic activity decrease for 10 runs of recycling due to the tightly anchored PIL on mesoporous SiO2 by copolymerization. And the catalytic activity to other substituted epoxides over mSiO2-PIL-2 was also expanded. Therefore, PIL anchored on mesoporous SiO2 by copolymerization could be a promising synthetic strategy for the efficient catalyst to combine multiple active components in a single catalyst, meanwhile, mSiO2-PIL-n exhibited an appealing catalyst candidate for the effective fixation and utilization of CO2.

An alternative low-cost, eco-friendly catalyst for hydrogen production

Simple two-step hydrothermal technique creates an improved non-metal catalyst to produce hydrogen for fuel.

Utilization of CO2-Available Organocatalysts for Reactions with Industrially Important Epoxides

Recent knowledge in chemistry has enabled the material utilization of greenhouse gas (CO2) for the production of organic carbonates using mild reaction conditions. Organic carbonates, especially cyclic carbonates, are applicable as green solvents, electrolytes in batteries, feedstock for fine chemicals and monomers for polycarbonate production. This review summarizes new developments in the ring opening of epoxides with subsequent CO2-based formation of cyclic carbonates. The review highlights recent and major developments for sustainable CO2 conversion from 2000 to the end of 2021 abstracted by Web of Science. The syntheses of epoxides, especially from bio-based raw materials, will be summarized, such as the types of raw material (vegetable oils or their esters) and the reaction conditions. The aim of this review is also to summarize and to compare the types of homogeneous non-metallic catalysts. The three reaction mechanisms for cyclic carbonate formation are presented, namely activation of the epoxide ring, CO2 activation and dual activation. Usually most effective catalysts described in the literature consist of powerful sources of nucleophile such as onium salt, of hydrogen bond donors and of tertiary amines used to combine epoxide activation for facile epoxide ring opening and CO2 activation for the subsequent smooth addition reaction and ring closure. The most active catalytic systems are capable of activating even internal epoxides such as epoxidized unsaturated fatty acid derivatives for the cycloaddition of CO2 under relatively mild conditions. In case of terminal epoxides such as epichlorohydrin, the effective utilization of diluted sources of CO2 such as flue gas is possible using the most active organocatalysts even at ambient pressure.

Collaboration of Ultrasonic Irradiation and Silica Nanoparticles in the Diastereoselective Synthesis of Trans-2,3-Dihydrofuran Derivatives: An Exceptional Catalytic Activity of Sound Cavities and SiO2 Nanoparticles

Coupling ultrasonic irradiation with nanoparticles has the potential to result in the synergistic mild and multi-component synthesis of valuable organic compounds. In this work, a fast and one-step strategy was developed for the diastereoselective synthesis of trans-2,3-dihydrofuran derivatives. The combination of ultrasonic waves and silica nanoparticles was promoted the eco-friendly condensation of aromatic aldehydes, 4-hydroxycoumarin, and phenacyl pyridinium bromide with each other in aqueous media smoothly. The method is fast, has high yields compared to the conventional method, low catalyst loading. The catalyst is inexpensive and very mild also is recyclable in six runs without appreciable loss of activity. This sonochemical assisted methodology is the first report of a green and unique one-pot process for the synthesis of trans-2,3-dihydrofurans over silica nanoparticles as a nonmetal oxide catalyst.

Dual-Atom Metal and Nonmetal Site Catalyst on a Single Nickel Atom Supported on a Hybridized BCN Nanosheet for Electrochemical CO2 Reduction to Methane: Combining High Activity and Selectivity.

Atomically dispersed nitrogen-coordinated transition-metal sites supported on graphene (TM-N4-C) offer promising potential for the electrochemical carbon dioxide reduction reaction (CO2RR). However, a few TM-Nx-C single-atom catalysts (SAC) are capable of reducing CO2 to multielectron products with high activity and selectivity. Herein, using density functional theory calculations, we investigated the electrocatalytic performance of a single TM atom embedded into a defective BCN nanosheet for CO2RR. The N and B atom co-coordinated TM center, namely, TM-B2N2, constructs a symmetry-breaking site, which strengthens the overlapping of atomic orbitals, and enables the linear CO2 to be curved and activated, compared to the weak coupling of CO2 with the symmetric TM-N4 site. Moreover, the TM-B2N2 sites play a role of dual-atom active sites, in which the TM atom serves as the carbon adsorption site and the B atom acts as the oxygen adsorption site, largely stabilizing the key intermediates, especially *COOH. The symmetry-breaking coordination structures shift the d-band center of the TM atom toward the Fermi level and thus facilitate CO2 reduction to hydrocarbons and oxygenates. As a result, different from the TM-N4-C structure that leads to CO as the major product, the Ni atom supported on BCN can selectively catalyze CO2 conversion into CH4, with an ultralow limiting potential of -0.07 V, while suppressing the hydrogen evolution reaction. Our finding suggests that introduction of a nonmetal active site adjacent to the metal site provides a new avenue for achieving efficient multi-intermediate electrocatalytic reactions.

Treated activated carbon as a metal-free catalyst for effectively catalytic reduction of toxic hexavalent chromium

In this work, activated carbon treated in N2 atmosphere, as a non-metallic catalyst, exhibits excellent catalytic performance in reduction of Cr (VI) to Cr (III) using HCOOH as the reducing agent at room temperature. A series of characterizations and control experiments were carried out to deduce the possible reaction mechanism. The results showed that the improved catalytic performance can be attributed to the enhanced graphitization degree and basic sites such as pyrone-like, which favor electron transferring and activation of reactant. The reaction rate constant observed herein for the C-800 was 22 and 6 times more than that for C-0 and Pd/C catalyst, respectively. In addition, C-800 showed good recycle performance, and no loss of activity was observed after 5 cycles. This study broadens the application of nonmetallic catalyst and provides an easy-available and cost-effective catalytic material for removing toxic Cr (VI).

Computational investigation on potential energy surface evolution: The tautomerization from enediyne to enyne-allene

1,3-proton transfer process is investigated theoretically on enediyne system with the help of different non-metallic catalysts. By tuning the substituents at the ene site and carefully selecting the catalyst, it is possible to manipulate the potential energy surface, where the reaction mechanism can be converted from fully concerted one, to “hidden transition state” concerted mechanism, and finally in a stepwise manner. Natural bond orbital interactions have revealed that the reaction mechanism is determined by the stability of the charge separated intermediate after deprotonation, where the interplay of the negatively charged substrate and the protonated catalysts plays the vital role.

A generalized approach to adjust the catalytic activity of borocarbonitride for alkane oxidative dehydrogenation reactions

The borocarbonitrides (BCNs) have exhibited enormous potential as non-metallic catalysts for alkane oxidative dehydrogenation (ODH) reactions. However, the poor electron transportation ability in BCN leads to a low reactivity of oxygen functional groups (CO and BOH). Herein, we present a generalized strategy to promote the catalytic activity of BCN through in situ encapsulation of transition-metal (Fe, Co, Ni) nanoparticles within BCN nanotubes (BCNNTs). Among them, individual metal particles themselves do not contribute directly on ODH reactions and mainly serve as electron modulators to tune the electron density of CO and BOH active sites on BCNNTs. As a result, catalytic activities of all metal@BCNNTs catalysts surpass pure BCN in ethylbenzene (EB) ODH reactions, among which Fe@BCNNTs displays a significant activity enhancement with 36 % EB conversion with the styrene (ST) selectivity remaining >98% under gentle reaction conditions. Structural and kinetic analyses proved that the promotion effect originated from the strong interactions between metal nanoparticles and BCNNTs. The theoretical calculations disclosed that the enhanced ODH activity was due to the electron transfer from the encapsulated metal to BCNNTs, which increases the electron transportation ability and electron density of BCNNTs, thus promoting the nucleophilicity of CO and BOH active sites, leading to the reduced activation energy barrier for CH bond dissociation. The present work sets forth the structure-function relationship, identifying opportunities for rational design of highly efficient BCN catalysts for ODH reactions.

Carbon Nitride is a Non-Metallic Catalyst for Oxygen Electrodes for Fuel Cells

A thermo chemical method for the synthesis of layered composites of graphite-like carbon nitride from urea and melamine has been developed. The production of graphite-like carbon nitride has been proven, SEM, X-ray diffraction, Raman spectroscopy and elemental analysis. Electrochemical studies have established that the obtained composites are promising materials as metal-free catalysts for oxygen electrodes for fuel cells.

Amorphous MoSxOy/h-BNxOy Nanohybrids: Synthesis and Dye Photodegradation.

Molybdenum sulfide is a very promising catalyst for the photodegradation of organic pollutants in water. Its photocatalytic activity arises from unsaturated sulfur bonds, and it increases with the introduction of structural defects and/or oxygen substitutions. Amorphous molybdenum sulfide (a-MoSxOy) with oxygen substitutions has many active sites, which create favorable conditions for enhanced catalytic activity. Here we present a new approach to the synthesis of a-MoSxOy and demonstrate its high activity in the photodegradation of the dye methylene blue (MB). The MoSxOy was deposited on hexagonal boron oxynitride (h-BNO) nanoflakes by reacting h-BNO, MoCl5, and H2S in dimethylformamide (DMF) at 250 °C. Both X-ray diffraction analysis and high-resolution TEM show the absence of crystalline order in a-MoSxOy. Based on the results of Raman and X-ray photoelectron spectroscopy, as well as analysis by the density functional theory (DFT) method, a chain structure of a-MoSxOy was proposed, consisting of MoS3 clusters with partial substitution of sulfur by oxygen. When a third of the sulfur atoms are replaced with oxygen, the band gap of a-MoSxOy is approximately 1.36 eV, and the valence and conduction bands are 0.74 eV and −0.62 eV, respectively (relative to a standard hydrogen electrode), which satisfies the conditions of photoinduced splitting of water. When illuminated with a mercury lamp, a-MoSxOy/h-BNxOy nanohybrids have a specific mass activity in MB photodegradation of approximately 5.51 mmol g−1 h−1, which is at least four times higher than so far reported values for nonmetal catalysts. The photocatalyst has been shown to be very stable and can be reused.

Unique capability of NdPO4 to activate hydrogen for efficient hydrogenation of furfural to furfuryl alcohol over Nd-Co-P composites

Efficient and applicable catalysts are highly desirable for advanced biomass transformation industry, here, we fabricated a series of Nd-Co-P catalysts for hydrogenation of furfural (FAL) to furfuryl alcohol (FOH). By comprehensive characterizations, it is demonstrated that the prepared Nd-Co-P samples are structured as (NdPO4)m/Co2P nanocomposites with molar ratio (m) in range of 0.24–1.1; by manipulating m, the outstanding catalytic efficiency comparable with the performance of precious metal catalysts, such as turnover frequency (TOF) up to 0.50 s−1 (being ten-fold higher than Co2P) and FOH yield up to 97%, is achieved on the reusable (NdPO4)m/Co2P composites. Temperature programmed desorption (TPD), in-situ infrared spectroscopy (IR) and kinetic-mechanism studies further disclose that Co2P is decisive for activating FAL, instead, NdPO4 possesses unique capability of activating hydrogen which readily facilitate the selective hydrogenation of FAL to FOH through a rapid Langmuir–Hinshelwood process over (NdPO4)m/Co2P catalyst. These results indicate that rare-earth phosphates like NdPO4 can act as the promising and reliable catalytic component to activate hydrogen, which can be of interest not only for innovating novel and applicable non-metallic catalysts for sustainable biomass transformation analogous to hydrogenation of FAL, but also for expanding material base for other green mass transformation techniques involving hydrogen.

Metal-Free Hyper-Cross-Linked Polymers from Benzyl Methyl Ethers: A Route to Polymerization Catalyst Recycling

New routes to porous materials can help lower production costs, improve sustainability, and broaden design options. Here, we use a selection of organic acids as catalysts in the synthesis of organic hyper-cross-linked polymers from benzyl methyl ether compounds. This approach provides a new route to metal-free porous organic polymers and addresses one of the largest setbacks of hyper-cross-linked polymers by allowing the simple recovery and recycling of a nonmetallic catalyst. By use of p-toluenesulfonic acid, a solid at room temperature, catalyst recovery rates of >80% were easily achieved. The catalyst was then reused as recovered in the further production of hyper-cross-linked polymers. Three rounds of catalyst recycling are demonstrated on two different aromatic systems, with no apparent detriment to the chemical or textural properties of the resulting networks.

Photocatalytic nitrate reduction by a non-metal catalyst h-BN: Performance and mechanism

It is highly desirable but challenging to control nitrate contamination using photocatalytic reduction technology over non-mental catalysts. Herein, hexagonal boron nitride (h-BN), a typical non-metal catalyst, was employed to photocatalytic denitration in water with formic acid (FA) as a hole scavenger. Compared with a mental catalyst TiO2 and a non-mental catalyst g-C3N4, h-BN obtained a more effective reduction performance with nitrate conversion of 97.16% and N2 selectivity of 95.42%. After three cyclic use, it still presented excellent reduction activity and structure stability. In the h-BN system, the initial pH had a significant effect on the nitrate reduction performance because it determined the surface charge property of the catalyst or the dispersibility in water, and the presence of anions slightly decreased the nitrate conversion process since the competitive adsorption of NO3– or NO2–. Photocatalytic denitration over h-BN was well according with the Extended-Langmuir-Hinshelwood model. By comparing the average stoichiometric ratio of consumed FA and removed NO3– (i.e. experiment value) with the theoretical value, it was determined that there were additional electrons involved in the reduction reaction in addition to CO2•- radicals, which was also supported by the quenching experiments. Moreover, CO2•- radicals were mainly responsible for the conversion of NO2– to N2. Exposed B atoms on the h-BN edges behaved as the adsorption sites of nitrogen oxide anions. This study provides a proof-of-concept demonstration of non-mental photocatalyst h-BN for more effective management of nitrate contamination.

A mechanistic periodic DFT study of CH, CO, and OH dissociations in methanol: M-doped carbon nanotubes (M=Pt, B, Al, N, P) versus Pt(100), Pt(110) and Pt(111) surfaces

• CO, CH, and OH dissociations in methanol are studied by using Pt(100), Pt(110), Pt(111), and doped CNT. • Dissociations are studied from both thermodynamics and kinetics points of view. • Theory shows that proposed SACs have less barrier energy for C−O dissociation compared to pure Pt surfaces. Periodic density functional theory is used to study adsorption and first step dissociation of methanol on M-doped carbon nanotubes (M = B, Al, Pt, N, and P) as a single atom catalyst (SAC). Data are compared with the adsorption and dissociation of methanol on Pt(100), Pt(110), and Pt(111). Only the first step of methanol dehydrogenation is investigated by considering three models of dissociations containing CH 3 + OH, CH 3 O + H, and CH 2 OH + H. The second model of dissociation is endothermic on all facets of Pt catalyst, but exothermic on B-, Al-, and Pt-doped carbon nanotube. The model of dissociation of CH 2 OH + H is more thermodynamically favorable on Pt(100), Pt(111), and Pt-doped carbon nanotube comparing to two other models. The most exothermic reaction belongs to the CH 3 + OH model on Al-doped carbon nanotube with -1.00 eV energy. Transition state calculations show that the barrier energy of C‒O dissociation on Al-doped carbon nanotube is 1.55 eV which is less than the barrier energies of C‒O dissociation on Pt(100), Pt(110), and Pt(111) which are 2.29, 2.45, and 1.96 eV. This shows that Al-doped carbon nanotube is a good candidate for alkylation catalyst. On the other hand B-doped carbon nanotube is a good non-metal catalyst for hydrogen production through O‒H dissociation.

Single-Atom Electrocatalysts for Multi-Electron Reduction of CO2.

The multi-electron reduction of CO2 to hydrocarbons or alcohols is highly attractive in a sustainable energy economy, and the rational design of electrocatalysts is vital to achieve these reactions efficiently. Single-atom electrocatalysts are promising candidates due to their well-defined coordination configurations and unique electronic structures, which are critical for delivering high activity and selectivity and may accelerate the explorations of the activity origin at atomic level as well. Although much effort has been devoted to multi-electron reduction of CO2 on single-atom electrocatalysts, there are still no reviews focusing on this emerging field and constructive perspectives are also urgent to be addressed. Herein recent advances in how to design efficient single-atom electrocatalysts for multi-electron reduction of CO2 , with emphasis on strategies in regulating the interactions between active sites and key reaction intermediates, are summarized. Such interactions are crucial in designing active sites for optimizing the multi-electron reduction steps and maximizing the catalytic performance. Different design strategies including regulation of metal centers, single-atom alloys, non-metal single-atom catalysts, and tandem catalysts, are discussed accordingly. Finally, current challenges and future opportunities for deep electroreduction of CO2 are proposed.

Microporous nitrogen-doped carbon from polyaniline as a highly efficient and stable catalyst for acetylene hydrochlorination

BackgroundAs a hot alternative to toxic industrial catalyst for acetylene hydrochlorination recently, N-doped carbon material (NC) catalysts have not yet exhibited both good activity and stability. MethodsHerein, NC catalysts with special physicochemical characteristics (abundant specific surface area and proper nitrogen content) were presented by the calcination of protonated polyaniline via chemical polymerization conditions. Significant FindingsA comparison of the performance between the novel catalysts and industrial 5% HgCl2/AC catalyst for acetylene hydrochlorination was evaluated under same acetylene gas hourly space velocity condition. The P-NC-1173-A6V12 catalyst exhibited a better initial acetylene conversion as well as stability at a high temperature reaction condition. The excellent catalytic stability is improved by the synergetic effect of abundant pore structure (especially micropores) and proper nitrogen species. In addition, carbon deposition is the main deactivation reason of catalyst. This work provides a facile method to prepare an environmentally friendly non-metallic catalyst with the potential for acetylene hydrochlorination.

Boosting hydrogen evolution reaction on few-layer graphdiyne by sp-N and B co-doping

Hydrogen evolution reaction (HER) catalysts based on noble metals traditionally suffered from high cost, low activity, and poor stability. Metal-free catalysts originating from heteroatom-doped carbon materials have been proposed to address these problems, in which the doping configurations and electronic structures are critical for modulating the electrocatalytic activity. Herein, we reported a sequential approach for the co-doping of B and N atoms into graphdiyne (GDY). We noticed that the configurations of heteroatoms are strongly related to the doping process, and the subsequent HER test shows that a certain sp-N can decrease the overpotential, and further introduction of B atoms can continuously enhance the current density owing to the synergistic effect of chemical and electronic couplings on proton adsorption/reduction kinetics. This work provides a deeper understanding of developing dual heteroatom doped non-metallic catalysts.