Pd-Decorated WTe2 Monolayer as a Favorable Sensing Material toward SF6 Decomposed Species: A DFT Study

Based on density functional theory, this work first investigates the Pd-decorating property on the pristine WTe₂ monolayer and then simulates the adsorption performance of a Pd-decorated WTe₂ (Pd-WTe₂) monolayer on SO₂ and SOF₂ molecules, in order to explore its sensing potential for SF₆ decomposed species. It is found that the Pd atom can be stably anchored on the top of the W atom of the WTe₂ monolayer with a binding energy of -2.43 eV. The Pd-WTe₂ monolayer performs chemisorption on SO₂ and SOF₂, with adsorption energies of -1.36 and -1.17 eV, respectively. The analyses of the band structure and density of states reveal the deformed electronic property of the WTe₂ monolayer by Pd-decoration, as well as that of the Pd-WTe₂ monolayer by gas adsorption. The bandgap of the Pd-Wte₂ monolayer is increased by 1.6% in the SO₂ system and is decreased by -3.9% in the SOF₂ system, accounting for the sensing response of 42.0 and -56.7% for the detection of two gases. Moreover, the changed work function (WF) in two gas systems in comparison with that of the pristine Pd-WTe₂ monolayer suggests its potential as a WF-based gas sensor for sensing two gases as well. This paper uncovers the gas sensing potential of the Pd-WTe₂ monolayer to evaluate the operation status of SF₆ insulation devices, which also illustrates the strong potential of WTe₂-based materials for gas sensing applications in some other fields.

N-doped carbon-modified palladium catalysts with superior water resistant performance for the oxidative removal of toxic aromatics

The supported palladium catalysts perform well in the oxidative removal of hazardous aromatic hydrocarbons. However, water vapor can seriously deactivate the catalysts especially in the low-temperature regime. Hence, improving moisture resistance of the Pd-based catalysts is full of challenge in the removal of aromatics. Herein, we report a new type of Pd@NC/BN catalysts featured with nitrogen-doped carbon layers modified Pd supported on hexagonal boron nitride (h-BN), and the relationship between structure and water resistance of the catalysts. The results show that in the presence of 10 vol% H₂O in the feedstock, the Pd@NC/BN catalyst could effectively oxidize o-xylene (with an almost 87% removal efficiency), whereas o-xylene conversion declined from 69% to 20% over the conventional Pd/Al₂O₃ at a reaction temperature of 210 °C and a space velocity of 40,000 mL/(g h). The adsorption of H₂O was significantly inhibited on the nitrogen-doped carbon layers due to the hydrophobic nature. Meanwhile, the oxygen species active for o-xylene oxidation were not only from the adsorbed gas-phase oxygen but also from the new active oxygen (*OOH and *OH) species that were generated via the interaction of O₂ and H₂O in the presence of water in the feedstock. It is concluded that the reactive oxygen species that accelerated the activation and cleavage of C-H bonds significantly facilitated the conversion of key intermediate species (from benzaldehyde to benzoic acid), thus playing a decisive role in o-xylene oxidation. The present work provides a direction for developing the superior water resistance catalysts with hydrophobic nature and good water activation ability in the oxidative removal of volatile organic compounds.

Novel joint catalytic properties of Fe and N co-doped graphene for CO oxidation

Using density functional theory, we have performed detailed calculations of the joint catalytic activity of graphene co-doped with Fe and N atoms. The Fe atom can be located on single vacancy graphene and acts as the active site. Due to the strong attraction of the Fe ion, the O-O bond length of the O2 molecule is elongated, which decreases the bonding energy between the O atoms. The energy barrier of CO oxidization is 0.84 eV. When N atoms are doped into the graphene, the interactions between the Fe ions and O2 molecules are stronger, and the O-O bond lengths are elongated further, which makes the desorption of the quasi-CO2 molecule easier. The energy barriers are reduced to 0.62 eV, 0.49 eV, and 0.33 eV for graphene doped with one, two and three N atoms, respectively. The O atom remaining on the Fe ion can form a CO2 molecule with an additional CO molecule. The produced CO2 molecule can be released with a small or even zero energy barrier by adsorbing an O2 molecule. The adsorbed O2 molecule is then involved in the next reaction process, and the material can be used as a recycled catalyst.

Unraveling Catalytic Mechanisms for CO Oxidation on Boron-Doped Fullerene: A Computational Study

By means of spin-polarized density functional theory (DFT) computations, we unravel the reaction mechanisms of catalytic CO oxidation on B-doped fullerene. It is shown that O2 species favors to be chemically adsorbed via side-on configuration at the hex-C-B site with an adsorption energy of -1.07 eV. Two traditional pathways, Eley-Rideal (ER) and Langmuir-Hinshelwood (LH) mechanisms, are considered for the CO oxidation starting from O2 adsorption. CO species is able to bind at the B-top site of the B-doped fullerene with an adsorption energy of -0.78 eV. Therefore, CO oxidation that occurs starting from CO adsorption is also taken into account. Second reaction of CO oxidation occurs by the reaction of CO + O → CO2 with a very high energy barrier of 1.56 eV. A trimolecular Eley-Rideal (TER) pathway is proposed to avoid leaving the O atom on the B-doped fullerene after the first CO oxidation. These predictions manifest that boron-doped fullerene is a potential metal-free catalyst for CO oxidation.

CO2 Electrochemical Reduction by Exohedral N-Pyridine Decorated Metal-Free Carbon Nanotubes

Electrochemical CO2 reduction reaction (CO2RR) to fuels and chemicals represents nowadays one of the most challenging solutions for renewable energy storage and utilization. Among the possible reaction pathways, CO2-to-CO conversion is the first (2e−) reduction step towards the production of a key-feedstock that holds great relevance for chemical industry. In this report we describe the electrocatalytic CO2-to-CO reduction by a series of tailored N-decorated carbon nanotubes to be employed as chemoselective metal-free electrocatalysts. The choice of an exohedral functionalization tool for the introduction of defined N-groups at the outer surface of carbon nanomaterials warrants a unique control on N-configuration and electronic charge density distribution at the dangling heterocycles. A comparative electrochemical screening of variably N-substituted carbon nanomaterials in CO2RR together with an analysis of the electronic charge density distribution at each heterocycle have suggested the existence of a coherent descriptor for the catalyst’s CO faradaic efficiency (FECO). Evidence allows to infer that N-configuration (N-pyridinic vs. N-pyrrolic) of exohedral dopants and electronic charge density distribution at the N-neighboring carbon atoms of each heterocycle are directly engaged in the activation and stabilization of CO2 and its reduction intermediates.

Co-doped triel-pnicogen graphene as metal-free catalyst for CO oxidation: Role of multi-center covalency

Third and fifth group atoms, named triel and pnicogen, respectively, were used for graphene doping. AlP and AlN structures were selected as co-doped graphene-based catalysts. The electronic structure and catalytic properties of binary AlN, AlP co-doped graphene were investigated through density functional theory (DFT). Results show that the AlP co-doped graphene strictly enhances the oxygen reactivity compared to AlN one. The CO oxidation on AlP and AlN co-doped graphene sheets is mainly done through Eley-Rideal mechanism as follows: CO + O₂➔CO₂ + O_ads and CO + O_ads➔ CO₂. The CO oxidation reaction paths over the AlN and AlP-co-doped graphene have revealed that they can be regarded as the competent catalyst for CO oxidation in the presence of O₂. Mechanistically, both AlP and AlN co-doped graphene catalysts are appropriately active in the first step while the second step is too hard to do regarding the multi-center covalency character between O₂ and AlP co-doped graphene and hence its catalytic efficiency is significantly lower compared to AlN co-doped graphene sheet. Thus, the substitution of a C-C bond with Al-N is an effective way to design the graphene-based catalysts for CO oxidation.

CO oxidization catalyzed by B, N, and their co-doped fullerenes: a first-principles investigation

The novel catalytic properties of the oxides of B and N, and their co-doped fullerenes are investigated.

UV-Assisted Cataluminescent Sensor for Carbon Monoxide Based on Oxygen-Functionalized g-C3N4 Nanomaterials

Cataluminescence (CTL) is one of the most important sensing-transduction principles for the real-time monitoring of atmospheric pollutants. Highly sensitive CTL-based CO detection still remains a challenge because of the relatively poor reactivity of CO and the low catalytic efficiency of the catalysts. Herein, combining ultraviolet (UV)-light activation and chemical modification of the sensing element, we have successfully established a UV-assisted CTL sensor for gaseous CO based on g-C₃N₄ with high sensitivity, selectivity, and stability. UV irradiation can efficiently activate CO molecules and induce the generation of reactive oxygen species (ROS) for CO oxidation. Furthermore, carboxyl groups greatly facilitate the chemisorption of CO on functionalized g-C₃N₄ nanomaterials, thus enhancing the CTL sensitivity. The influences of experimental conditions and the possible catalytic mechanism of CO on functionalized g-C₃N₄ have been investigated in detail. Under the optimal experimental conditions, the proposed CTL sensor presents a detection limit (3σ) toward CO of 0.008 μg mL^-1, which is much lower than the maximum allowable emission concentration of CO in atmospheric conditions (0.030 μg mL^-1). The UV-CTL system is green, sensitive, stable, and low cost, and thus it possesses great potential application in gas sensing.

Can molten carbonate be a non-metal catalyst for CO oxidation?

For the first time, we have examined molten carbonate as a non-metal catalyst for CO oxidation in the temperature range of 300–600 °C.

Catalytic CO oxidation on B-doped and BN co-doped penta-graphene: a computational study

The catalytic reaction of carbon monoxide oxidation on boron-doped and boron–nitrogen co-doped penta-graphene materials has been systematically studied by utilizing spin-polarized density functional theory (DFT) calculations.

A promising single atom catalyst for CO oxidation: Ag on boron vacancies of h-BN sheets

Due to “CO-Promoted O₂ Activation”, the termolecular Eley–Rideal (TER) mechanism is the most relevant one for CO oxidation over the SAC, Ag₁/BN.