Metal-free Catalyst For CO Oxidation Research Articles

Catalytic properties of cyclo-carbon clusters: An investigation on o[formula omitted] activation and CO oxidation

The carbon allotrope-based catalysts attracted considerable attention for oxidation–reduction reactions due to their low-cost and environmentally friendly properties. Systematic investigations are required to explore the catalytic properties and corresponding mechanisms of the new discovered carbon allotropes such as cyclocarbon clusters (cyclo-Cn). Here, using first-principles calculations, we study the stability and electronic properties of cycloCn. Regarding the spin multiplicity and geometry of cycloCn the electronic properties of n-odd and n-even cycloCn were found to be significantly different. Also, based on the EleyRideal (ER) and LangmuirHinshelwood (LH) mechanisms, we focus on the CO oxidation over sp-hybridized molecular carbon allotropes (cyclo-Cn) including recently synthesized cycloC18 by Kaiser, K. et al. (Science2019 365(6459), 1299–1301). In particular, thirteen cycloCn (with n=12-24) are studied. It was found that these carbon clusters may be useful for CO oxidation. We also elucidate the effects of NaCl(100) substrate on the catalytic performance of two cycloCn (n=17, 18) where we found that their optimized structures and the corresponding energy barriers are not very different than that of isolated molecular allotropes. The results show that cycloCn clusters may be a metal-free catalyst for CO oxidation. However, the stability of the cycloCn is a major concern under the acidic or basic conditions required for oxygen electrocatalysis that other groups must consider for further in situ calculations and characterizations.

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.

C20 fullerene and its boron- and nitrogen-doped counterparts as an efficient catalyst for CO oxidation

DFT calculations are utilised to investigate the CO oxidation on the C20, BC19, and NC19 clusters. For CO oxidation over considered clusters, two continuous steps are proposed that in each step one CO2 molecule is released from clusters surface. The calculations demonstrate that in the case of the C20 cluster, the first step of CO oxidation takes place through the ER mechanism on two routes with a barrier height of 1.06 eV and 2.57 eV for the rate-limiting step. Also, in the cases of BC19 and NC19 clusters, both reaction paths occur via the ER mechanism. The activation energy of the first reaction step is about 0.53 and 0.46 eV, while it is negligible for the second step that is 0.04 and 0.18 eV for BC19 and NC19 clusters, respectively. Based on the present theoretical results, the catalytic activity of BC19 and NC19 clusters toward the CO oxidation is more than that of the C20 cluster. These results show that the BC19 and NC19 clusters can be recommended as an efficient and metal-free catalyst for CO oxidation at near ambient temperatures. Research Highlights CO oxidation over C20 fullerene has been investigated. The effect of N/B-doing on the CO oxidation reaction is also studied. The N/B-doping increases the catalytic activity of C20 fullerene. Boron/Nitrogen-doped C20 fullerene can be applied as an efficient catalyst for CO oxidation.

Photocatalysis enhanced cataluminescence gas sensor for carbon monoxide based on perylenetetracarboxylic diimide

The rapid and sensitive detection techniques for CO are highly essential for public health and environmental pollution. Herein, a photocatalysis enhanced cataluminescence (CTL) gas sensor with metal-free catalyst for CO was developed. Due to the low CTL reaction activity of CO, photocatalysis which could activate CO was chosen as effective signal amplification technology to improve response sensitivity of CO. Meanwhile, self-assembled 3,4,9,10-Perylenetetracarboxylic Diimide (PDINH), which has stacked ordered structure with π-π stacking, was first used as metal-free catalyst for CO oxidation in CTL process. The π-π stacking and layered structure in PDINH are beneficial for the adsorption of O2 and CO. Therefore, amplified CTL signal was acquired because of the important role of photocatalysis and the sensing material in CTL process. Under the optimal experimental conditions, a detection limit (3σ) of 0.002 μg mL−1 CO is found in the proposed method, which has been further improved comparing to that of without photocatalysis. The realization of combining photocatalysis with CTL for the first time gives us a perspective on building a new pretreatment strategy for CTL detection.

CO oxidation by linear oxocarbon chains Ox-Cn-Ox (n = 5–10, x = 1, 2): A theoretical study

Catalyst based on allotropes of carbon drew considerable attention for oxidation reduction-reactions (ORRs) by reason of their low-cost and environmentally friendly features. However, new researches are required to gain further understanding of the catalytic properties of the novel investigated allotropes of carbon. In this communication, first-principles calculations have been used via an ER mechanism to study CO oxidation over a new allotrope of carbon called mono-atomic carbon chains (MACCs) particularly on O2 activated MACCs derivatives i.e., oxocarbon chains Ox-Cn-Ox (n = 5–10, x = 1,2). By considering 30 oxocarbon chains, it is found that for x = 2 and x = 1, n-odd and n-even chains are preferred for CO oxidation, respectively. The energy barrier is predicted to be in a range of 0.80–5.10 eV. These predicted values in some cases are in agreement with those processes catalyzed by other allotropes of carbon. Interestingly, the results are demonstrated that MACCs are a promising and metal-free catalyst for CO oxidation.

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 + Oads and CO + Oads➔ 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.

Exploring reaction mechanisms for CO oxidation on boron-doped carbon nanotubes: A computational approach

Spin-polarized first-principles computations are carried out to illustrate the catalytic mechanisms of CO oxidation on the (5, 5) boron-doped carbon nanotube (BCNT). BCNTs with two kind of boron content of 1 and 2 atom % are studied. The calculations show that O2 species prefers to partially reduce and chemically bind at CB site via the side-on configuration with the adsorption energies of −0.85 eV for the BCNT with boron content of 1 atom % and −1.27 ~ −1.29 eV for the BCNT with boron content of 2 atom %. The partially reduced O2 species can further react with CO via the Eley-Rideal (ER) mechanism by overcoming a small energy barrier of 0.34 eV for the BCNT with boron content of 1 atom % and 0.42 eV for the BCNT with boron content of 2 atom %. Second reaction of CO oxidation occurs by the reaction of CO + O → CO2 with a slight energy barriers of 0.12 and 0.14 eV for the BCNT with boron content of 1 and 2 atom %, respectively. Our results manifest that the boron-doped CNT can be an advanced metal-free catalyst for CO oxidation.

CO oxidation over BC3 nanosheet: a theoretical study

ABSTRACTMetal-free catalysts have attracted more attention due to their highly active in catalytic oxidation reactions. The electronic structure and catalytic property of BC3 sheet are investigated by using first-principles calculations. It is found that the BC3 sheet as the active surface can effectively regulate the adsorptive stability of reactive gases. Besides, the possible reaction processes for CO oxidation on the BC3 sheet are comparably analysed through different reaction mechanisms, which include the Eley–Rideal (ER), Langmuir–Hinshelwood (LH) and termolecular Eley–Rideal (TER). In the CO oxidation reactions, the decomposition of O2 molecule as the starting state (0.40 eV) is an energetically more favourable process than those of other processes, the Eley–Rideal (ER) reactions (2Oads+2CO→CO2) are more prone to take place with lower energy barriers (< 0.20 eV) on the BC3 sheet. These results provide an important guidance on exploring the highly efficiency metal-free catalyst for CO oxidation.

Probing reaction pathways for oxidation of CO by O2 molecule over P-doped divacancy graphene: A DFT study

Using the dispersion-corrected density functional theory calculations, the catalytic performance of P-doped graphene with divacancy (P-GDV) is examined for the oxidation of CO by O2 molecule. According to our results, the first step of CO oxidation (CO + O2 → CO2 + O∗) proceeds via Langmuir–Hinshelwood mechanism with a small activation energy (0.28 eV). The remaining O atom (O∗) is then eliminated by another incoming CO molecule with an energy barrier of 0.59 eV. It is found that the orbital hybridization between the O2-2π and CO-2π∗ states in the coadsorbed structure plays an important role for the first step of the CO oxidation. Our result indicates that the low-cost P-GDV can be regarded as an active metal-free catalyst for CO oxidation at room temperature.

A new carbon allotrope: Penta-graphene as a metal-free catalyst for CO oxidation

We performed first-principles calculations to study CO oxidation on a new carbon allotrope called penta-graphene (PG). The CO oxidation involves CO + O2 → CO2 + O and CO + O → CO2 reactions considering through Eley–Rideal (ER) and Langmuir–Hinshelwood (LH) mechanisms. The ER mechanism proceeds the oxidization of CO to CO2 by the pre-adsorbed O2 on the PG sheet. The energy barrier is predicted to be 0.65 eV. The LH mechanism takes place by co-adsorbed CO and O2 on PG sheet with an energy barrier as low as 0.31 eV. These predicted values are quite close to those processes catalyzed by noble metals. In addition, we analyzed the LDOS at each step of ER and LH mechanisms to deeply understand the catalytic properties of PG. Our calculation results illustrate that PG is a potential, metal-free, and low-cost catalyst for low-temperature CO oxidation. This study contributes to designing more effective carbon allotrope catalysts and widening the applications of carbon allotrope.

Nitrogen coordinated silicon-doped graphene as a potential alternative metal-free catalyst for CO oxidation

Metal-free catalysts have attracted more attention due to their highly active in catalytic oxidation reactions. The outstanding stability and catalytic activity of a single-atom Si incorporated N4 centers in graphene (Si-GN4) are investigated using first-principles calculations. It is found that the Si-GN4 configuration can be stable at high temperature, the positively charged Si dopant as the active center can effectively regulate the adsorption of reactive gases (CO and O2). Besides, the possible reaction processes of CO oxidations on the Si-GN4 surface through the Eley−Rideal (ER) mechanism are comparably analyzed. In the CO oxidation reactions, the preadsorbed O2 reacts with CO to form OOCO complex with smaller energy barrier (0.57 eV) than those of the formed CO3 complex (1.08 eV) and the dissociated O2 reaction (0.74 eV), indicating that this reaction as starting stare is an energetically more favorable process. This result indicates that the much stable Si-GN4 sheet will be a highly efficient catalyst for CO oxidation, which is comparable to that of the noble metal catalyst.

CO oxidation catalyzed by silicon carbide (SiC) monolayer: A theoretical study

Developing metal−free catalysts for CO oxidation has been a key scientific issue in solving the growing environmental problems caused by CO emission. In this work, the potential of the silicon carbide (SiC) monolayer as a metal−free catalyst for CO oxidation was systematically explored by means of density functional theory (DFT) computations. Our results revealed that CO oxidation reaction can easily proceed on SiC nanosheet, and a three-step mechanism was proposed: (1) the coadsorption of CO and O2 molecules, followed by (2) the formation of the first CO2 molecule, and (3) the recovery of catalyst by a second CO molecule. The last step is the rate−determining one of the whole catalytic reaction with the highest barrier of 0.65eV. Remarkably, larger curvature is found to have a negative effect on the catalytic performance of SiC nanosheet for CO oxidation. Therefore, our results suggested that flat SiC monolayer is a promising metal-free catalyst for CO oxidation.

Nitrogen-doped carbon nanotube as a potential metal-free catalyst for CO oxidation.

We elucidate the possibility of nitrogen-doped carbon nanotube as a robust catalyst for CO oxidation. We have performed first-principles calculations considering the spin-polarization effect to demonstrate the reaction of CO oxidation catalyzed by the nitrogen-doped carbon nanotube. The calculations show that O2 species can be partially reduced with charge transfer from the nitrogen-doped carbon nanotube and directly chemisorbed on the C-N sites of the nitrogen-doped carbon nanotube. The partially reduced O2 species at the C-N sites can further directly react with a CO molecule via the Eley-Rideal mechanism with the barriers of 0.45-0.58 eV for the different diameter of nanotube. Ab initio molecular dynamics (AIMD) simulations were performed and showed that the oxidation of CO occurs by the Eley-Rideal mechanism. The relationship between the curvature and reactivity of the nitrogen doped carbon nanotube was also unraveled. It appears that the barrier height of the rate-limiting step depends on the curvature of the nitrogen-doped carbon nanotube in the trend of (3,3)-NCNT < (4,4)-NCNT < (5,5)-NCNT (decreases with increased curvature). Using this relationship, we can predict the barriers for other N-doped carbon nanotubes with different tube diameters. Our results reveal that the nitrogen doped carbon nanomaterials can be a good, low-cost, and metal-free catalyst for CO oxidation.

Can Si-embedded boron nitride nanotubes act as a favorable metal-free catalyst for CO oxidation by N2O?

N2O adsorption over Si-doped BNNT.

Si-embedded graphene: an efficient and metal-free catalyst for CO oxidation by N2O or O2

As is well known, searching for an efficient catalyst for CO oxidation is of great importance in the removal of poisonous CO gas. From the results of density functional theory calculations, we have reported the catalytic oxidation of CO by O2 or N2O on Si-embedded graphene. Both Langmuir–Hinshelwood and Eley–Rideal mechanisms of CO oxidation on Si-embedded graphene were comparably studied. The results indicate that CO oxidation by O2 on Si-embedded can occur via a two-step mechanism: (1) CO + O2 → OOCO → CO2 + O, followed by (2) CO + O → CO2. The energy barriers for the two steps are 0.48 and 0.57 eV, respectively. For N2O + CO → N2 + CO2, N2O firstly interacts with Si-embedded graphene, releasing N2 and leaving the O-atom to be attacked by the subsequent CO to yield CO2 to proceed with the catalytic cycle. The present results provide a useful guidance to fabricate metal - free graphene-based catalysts for CO oxidation with low cost and high activity.