Coadsorption Of O2 Research Articles

Low-temperature catalytic performance improvement of Ru/TiO2{001} for o-dichlorobenzene oxidation

Chlorinated aromatics hydrocarbons were harmful to ecology and human health, whose catalytic combustion encounters problem of catalyst deactivation by chlorine poisoning. To simultaneously improve the catalytic activity, CO2 selectivity and stability of catalyst, the present study used the loading of Ru active component on the anatase TiO2 which preferentially exposes highly active {001} crystalline facets. Take o-dichlorobenzene (o-DCB) oxidation as a surrogate reaction, Ru/TiO2{001} showed lower T90% (temperatures with 90% conversion), higher CO2 selectivity and better stability than Pt/TiO2{001}, Pd/TiO2{001} and Ru/commercial TiO2 (Ru/TiO2-C). The excellent results could be attributed to the strong metal support interaction between Ru species and TiO2{001}, with more oxygen vacancies and higher surface oxygen concentration, more Lewis acid sites, enhanced low-temperature reducibility, more surface Ti3+ species, more surface Ru4+ species, and highly dispersed Ru species, favoring the excellent low temperature catalytic activity and CO2 selectivity of Ru/TiO2{001}. In addition, the less Cl species on the used 1.5% Ru/TiO2{001} indicated their effectively removal, which is the core issue for the deep oxidation of o-DCB. Furthermore, the in situ FTIR spectroscopy gave the detail oxidation route of o-DCB over 1.5% Ru/TiO2{001}, that the co-adsorption of o-DCB and O2 on Ru/TiO2{001} surface were calculated based on the density functional theory calculations. The present study gave a new insight into the new pathway for the design of promising catalysts for the treatment of CAHs.

A unique air-assisted DMSO oxidation pathway for the highly efficient synthesis of 2,5-diformylfuran from 5-hydroxymethylfurfural/fructose

A unique air-assisted DMSO oxidation pathway is activated by the co-adsorption of DMSO and O2 on Co-(pyrrolic N–C) pairs of CoNC-MCM.

Reactant adsorption modulation by Fe and K in Pt catalyst for highly effective CO preferential oxidation in practical conditions

Developing efficient and stable catalysts for preferential oxidation of CO (CO-PROX) within a wide temperature window is significant for the industrial hydrogen resource purification process. Herein, dual promoters of Fe and K were deliberately introduced to the mordenite supported Pt catalyst for optimizing the adsorption behaviors of reactants in CO-PROX. The optimal 1Pt0.1 K/Fe-MOR catalyst can achieve 100% CO conversion and 60–70% CO2 selectivity (the ratio of CO/O2 is 1:1) under the realistic application temperature range (130–200 °C), and remains catalytically stable during 65 h testing at 140 °C. A combination of detailed characterizations and density functional theory (DFT) simulations show that Fe species can avoid the co-adsorption of O2 on the Pt sites by providing more oxygen vacancy to activate O2, while K species will further enhance the adsorption of CO and repulse the adsorption of H2 on Pt surface. Therefore, the optimized adsorption of CO, O2 and H2 results in a total CO conversion and high CO2 selectivity in high temperature range.

The interaction of H2O, O2 and H2O + O2 molecules with g-C3N4 surface:A first-principle study

The interactions between H2O, O2, H2O + O2 and graphene carbon nitride (g-C3N4) surface were investigated by using first-principle method. The results indicated that the N atoms near the bridge sites and vacancies for g-C3N4 surface have high activity, which can promote the dissociation of water molecules and form hydrogen bonds after water and oxygen adsorption. The H2O and O2 molecules are not dissociated for only H2O or O2 molecules adsorption on g-C3N4 surface, and the hydrogen bonds are formed after H2O molecule adsorption. Two oxygen atoms of O2 molecule are bonded to carbon and nitrogen atoms of g-C3N4 surface respectively after O2 adsorption. There are two stable configurations for H2O + O2 co-adsorption on g-C3N4 surface (MA and MC), and their adsorption energies are −57.35 kJ/mol, −61.10 kJ/mol, respectively. For the MA, two oxygen atoms of O2 molecule are bonded to C and N atoms of g-C3N4 surface, respectively, and one hydrogen bond is formed between H2O and O2 molecules. As for the MC, three hydrogen bonds are formed in the interface of H2O + O2 and g-C3N4 surface. H2O molecule is dissociated, and O2 molecule turns to superoxide radical by gaining electrons. The formation of superoxide radical contributes to the degradation of organic pollutants for g-C3N4.

Theoretical studies of MXene-supported single-atom catalysts: Os1/Ti2CS2 for low-temperature CO oxidation

We report herein a new sulfur-functionalized MXene Ti2C (Ti2CS2)-supported osmium-metal single-atom catalyst (SAC) Os1/Ti2CS2 with high low-temperature catalytic activity for CO oxidation. Using periodic density functional theory calculations, the most stable SAC, Os1/Ti2CS2, has been screened from a series of group 8–11 transition metal SACs M1/Ti2CS2 (M = Fe, Co, Ni, Cu; Ru, Rh, Pd, Ag; Os, Ir, Pt, Au). The calculations show that it is favorable for O2 and CO to be coadsorbed on the Os1 single atom (SA) of Os1/Ti2CS2 and the adsorption energy of the first O2 molecule is slightly higher than that of CO. Moreover, the termolecular co-adsorption of O2 + 2CO on Os1 SA is also possible, which is favorable for CO oxidation on Os1 SA through a novel three-molecule reaction mechanism. Accordingly, four different catalytic mechanisms, the Langmuir-Hinshelwood (L-H), Eley-Rideal (E-R), termolecular Langmuir-Hinshelwood-A (TLH-A) and termolecular Langmuir-Hinshelwood-B (TLH-B), are systematically studied for CO oxidation by O2 on Os1/Ti2CS2. The theoretical studies indicate that the TLH-B mechanism is the most feasible for CO oxidation with the reaction barrier energy of only 0.74 eV, which is far lower than for L-H, E-R and TLH-A with barrier energies of 1.06, 1.09 and 1.47 eV, respectively. The results provide fundamental understanding to the surface chemistry of MXene and designing new sulfur-functionalized two-dimensional MXene catalytic nanomaterials.

A mechanistic DFT study of selective ethylene oxidation to ethylene oxide catalyzed by Pd-doped C3N monolayer

The selective epoxidation of ethylene on Pd-doped C3N nanosheet (Pd@C3N) is investigated using dispersion-corrected DFT calculations. The electronic resonance between the Pd and its neighboring C atoms is shown to significantly activate the adsorbed O2 and C2H4 molecules on Pd@C3N. According to our results, the coadsorption of O2 and C2H4 molecules on Pd@C3N is more energetically feasible than a single O2 or C2H4 adsorption. The oxidation of ethylene on Pd@C3N is accomplished via two mechanisms, i.e., bimolecular (B-LH) and trimolecular Langmuir–Hinshelwood (T-LH). In both pathways, the ethylene oxide formation is favored over the acetaldehyde formation. The obtained activation barriers are comparable to those reported for Au-based catalysts. Moreover, the epoxidation of ethylene has a faster kinetics than the formation of acetaldehyde. Also, the effects of temperature and entropy are studied on the rate-determining steps of the B-LH and T-LH mechanisms.

Adsorption of NO and O2 on MnO2 and (MnO2)3/Al2O3

Based on first-principles density functional theory (DFT), the adsorption performance of MnO2(110) surface for NO and O2 was calculated, and the deposition of (MnO2)3cluster on the γ-Al2O3(110) surface was studied. In addition, the adsorption and co-adsorption of NO and O2 on the surface of (MnO2)3/Al2O3 were further calculated. The results showed that NO was more inclined to adsorb on the four-coordinated Mn(Ⅳ) sites on the MnO2(110) surface (the maximum Eads was −75.35KJ·mol−1). There were very few O2 adsorption sites on the MnO2(110) surface, and only the vacancies between adjacent Mn(IV) could adsorb O2 stably. PDOS analysis showed that the hybridization between Mn 3d orbital and N 2p (or O 2p) orbital was the main reason for Mn-N bonds (or Mn-O bonds). The (MnO2)3 cluster tended to load on Al2O3(110) surface in a flat six-membered ring structure. There are abundant active oxygen sites on the (MnO2)3/Al2O3 surface, which had an excellent ability to adsorb NO (the maximum Eads was −278.24 KJ·mol−1). NO molecules interacted with surface-active oxygen to generate nitroso, and NO2 was easily desorbed from the (MnO2)3/Al2O3 surface. The co-adsorption of NO and O2 on the (MnO2)3/Al2O3 surface formed an ONOO* structure, which could decompose to form adsorbed NO2* and O*. Compared with single-phase manganese oxide crystals, manganese oxide clustered on γ-Al2O3 had superior NO adsorption performance and may have excellent catalytic oxidation properties.

H2O and O2 co-adsorption on 3C-SiC (111) by first-principle calculations: The role of water in initial oxidation

First-principle calculations were employed to investigate the initial oxidation behaviors of CVD-SiC in wet oxygen. The H2O/O2 co-adsorption behaviors with different H2O/O2 molecular ratios and coverages on (3 × 3) 3C-SiC (111) surface were studied by geometry optimization and property calculation. The results showed that the OO bond in SiOO structure had higher bond energy than that in Si-O-O-H structure, indicating the weaker bond energy of OO bond in the formed hydroperoxyl. First-principle molecular dynamic (FPMD) simulations confirmed that the formation of hydroperoxyl as an intermediate was feasible during the dissociation of molecular oxygen, which played an important role in O2 activation. The static calculation results indicated that the formation of hydroperoxyl needed to experience a lower activation energy barrier (0.35 eV), which demonstrated more likely occurrence than the direct dissociation of molecular oxygen. In brief, the introduction of molecular water could enhance the oxidation rate of 3C-SiC in initial stage by the formation of hydroperoxyl. This work revealed the initial oxidation mechanism of 3C-SiC (111) in wet oxygen and the role of water in initial oxidation, which could also provide a new view to explain the accelerated oxidation rate of SiC in wet oxygen.

CO oxidation over defective and nonmetal doped MoS2 monolayers

Defective (missing S atoms) and nonmetal (C- and N-) doped MoS2 monolayers in the 2H and 1T′ phases have been evaluated for catalyzing CO oxidation based on first-principles calculations. For the reaction 2CO + O2 → 2CO2, the oxidization of the first CO molecule is fairly easy and sometimes is even spontaneous, as the O2 molecule is highly activated or dissociates upon adsorption. However, for the defective (2H-), C-doped (1T′-), and N-doped (2H- and 1T′-) MoS2 monolayers, the remaining O* adatom often refuses to react with other CO molecules and is hard to be removed (barrier > 1.20 eV). Only when over the C-doped 2H- and defective 1T′-MoS2 monolayers, the removal of the second O* adatom requires to overcome moderate barriers (0.74 and 0.88 eV, respectively) by reacting with another CO molecule via the Eley–Rideal mechanism and the catalysts are recovered. The barriers can be further reduced by applying either tensile or compressive strain to the MoS2 nanosheet. In contrast, the Langmuir–Hinshelwood mechanism is followed over the metal-containing MoS2 nanosheets, as the bigger size of metal dopants allow the co-adsorption of CO and O2. Therefore, the C-doped 2H- and defective 1T′-MoS2 monolayers are promising nonmetal-doped catalysts for CO oxidation.

CO oxidation on Ni and Cu embedded graphdiyne as efficient noble metal-free catalysts: A first-principles density-functional theory investigation

Single atom catalysts (SACs) have become the research hotspot on account of the maximum usage of the metal atom and have exhibited preferable catalytic activity. As a new allotrope of carbon, graphdiyne (GDY) has been proposed to be a potential substrate for SACs. CO oxidation on GDY embedded with Ni and Cu atoms (Ni-GDY and Cu-GDY), as a prototype reaction, has been systematically investigated by first-principles density-functional theory calculations. The calculated results show that both Ni and Cu atoms tend to embed at the corner of the acetylenic ring of GDY and the diffusion barriers of Ni and Cu atoms on GDY are rather high. Furthermore, the CO oxidation via Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms are compared. Since the adsorption of CO on Ni-GDY or co-adsorption of CO and O2 on Cu-GDY is more favorable than the adsorption of O2, the CO oxidation prefers to begin with LH reaction with a lower energy barrier and further proceeds with ER reaction. The calculated results presented here demonstrate that GDY is believed to be a promising SAC substrate for CO oxidation, which also provide deeper insights into the design of novel heterogeneous catalysts based on GDY.

Unveiling the importance of reactant mass transfer in environmental catalysis: Taking catalytic chlorobenzene oxidation as an example

To date, investigations onto the regulation of reactants mass transfer has been paid much less attention in environmental catalysis. Herein, we demonstrated that by rationally designing the adsorption sites of multi-reactants, the pollutant destruction efficiency, product selectivity, reaction stability and secondary pollution have been all affected in the catalytic chlorobenzene oxidation (CBCO). Experimental results revealed that the co-adsorption of chlorobenzene (CB) and gaseous O2 at the oxygen vacancies of CeO2 led to remarkably high CO2 generation, owning to their short mass transfer distance on the catalyst surface, while their separated adsorptions at Brönsted HZSM-5 and CeO2 vacancies resulted in a much lower CO2 generation, and produced significant polychlorinated byproducts in the off-gas. However, this separated adsorption model yielded superior long-term stability for the CeO2/HZSM-5 catalyst, owning to the protection of CeO2 oxygen vacancies from Cl poisoning by the preferential adsorption of CB on the Brönsted acidic sites. This work unveils that design of environmental catalysts needs to consider both of the catalyst intrinsic property and reactant mass transfer; investigations of the latter could pave a new way for the development of highly efficient catalysts towards environmental pollution control.

Formation, electronic, gas sensing and catalytic characteristics of graphene-like materials: A first-principles study

The formation geometry, electronic property, gas sensing and reactive activity of single-atom Fe anchored on different nanoporous carbon materials (graphenylene-Fe and γ-graphyne-Fe) are comparably analyzed by using first-principles calculations. Firstly, the graphenylene structure is more stable than that of γ-graphyne sheet. The varied strains (from −10% to +10%) can regulate the metal and semiconducting properties of graphenylene sheet. Compared with the γ-graphyne-Fe, the single or two reactive gases have larger adsorption energies on graphenylene-Fe sheet. Meanwhile, the electronic structures and magnetic properties of graphenylene-Fe can be modified by these adsorbed species. Secondly, the coadsorbed configurations of different gas reactants on two kinds of γ-graphyne-Fe and graphenylene-Fe sheets are further analyzed for the catalytic oxidation of NO and CO. By the Langmuir–Hinshelwood (LH) mechanism, the coadsorption of CO and O2 on graphenylene-Fe has lower reaction barriers than the same mechanism for NO oxidation. Furthermore, the adsorbed 2NO molecules can promote the oxidation reactions of 2CO (2NO + 2CO → 2CO2 + N2) through Eley − Rideal (ER) mechanism (<0.6 eV), which provides a theoretical reference on exploring new nanoporous graphene-like catalyst for toxic gases removal.

Catalytic oxidation of CO over Pt/Fe3O4 catalysts: Tuning O2 activation and CO adsorption

The self-inhibition behavior due to CO poisoning on Pt metal particles strongly impairs the performance of CO oxidation. It is an effective method to use reducible metal oxides for supporting Pt metal particles to avoid self-inhibition and to improve catalytic performance. In this work, we used in situ reductions of chloroplatinic acid on commercial Fe3O4 powder to prepare heterogeneousstructured Pt/Fe3O4 catalysts in the solution of ethylene glycol. The heterogeneous Pt/Fe3O4 catalysts achieved a better catalytic performance of CO oxidation compared with the Fe3O4 powder. The temperatures of 50% and 90% CO conversion were achieved above 260°C and 290°C at Pt/Fe3O4, respectively. However, they are accomplished on Fe3O4 at temperatures higher than 310°C. XRD, XPS, and H2-TPR results confirmed that the metallic Pt atoms have a strong synergistic interaction with the Fe3O4 supports. TGA results and transient DRIFTS results proved that the Pt metal particles facilitate the release of lattice oxygen and the formation of oxygen vacancies on Fe3O4. The combined results of O2-TPD and DRIFTS indicated that the activation step of oxygen molecules at surface oxygen vacancies could potentially be the rate-determining step of the catalytic CO oxidation at Pt/ Fe3O4 catalysts. The reaction pathway involves a Pt-assisted Mars-van Krevelen (MvK) mechanism.

Catalytic ethylene oxidation by Cu–Au core–shell nanoclusters: a computational study

We have studied the catalytic activity of Cu–Au core–shell nanoclusters toward the ethylene oxidation based on periodic first-principles computations. The adsorption behaviors of O2 and C2H4 on the Cu–Au core–shell nanoclusters as well as the C2H4–O2 coadsorption were examined. We found that O2 and C2H4 are preferably bound at bridge (B) and top (T) sites with adsorption energies of − 2.09 and − 0.65 eV for Cu32–Au6 nanocluster and − 1.06 and − 0.62 eV for Au32–Cu6 nanocluster. The oxidation reaction occurs via the Langmuir–Hinshelwood (LH) mechanism which has been illustrated by employing the climbing image nudged elastic band method. The overall reaction of O2 + C2H4 → epoxide + O is exothermic by ~ 3.31 eV for Cu32–Au6 nanocluster and 2.17–2.26 eV for Au32–Cu6 nanocluster, while those are 3.76–4.24 eV and 2.91–2.73 eV for the generation of acetaldehyde. The Cu–Au core–shell nanoclusters, especially the hexagonal fcc(111)-like face of Cu32–Au6 and the square fcc(100)-like face of Au32–Cu6 core–shell nanoclusters, exhibit better catalytic properties and selectivity for the ethylene oxidation compared with the Cu and Au nanoparticles.

Catalytic Enhancement of CO Oxidation on LaFeO3 Regulated by Ruddlesden-Popper Stacking Faults.

The influence of planar defects, in the form of stacking faults, within perovskite oxides on catalytic activity has received little attention because controlling stacking-fault densities presents a major synthetic challenge. Furthermore, stacking faults in ceramics are not thought to appreciably impact surface chemistry, which partly explains why their direct effect on catalysis is generally ignored. Here, we show that Ruddlesden-Popper (RP) stacking faults in otherwise stoichiometric LaFeO3 can be broadly controlled by modulating the ceramic synthesis route. Electronic structure calculations along with electron microscopy and spectroscopy show that energetically favorable RP faults occur both near the surface and in bunches and enhance CO oxidation kinetics. Density functional theory (DFT) + U shows that subsurface RP faults strengthen the adsorption and co-adsorption of CO, O, and O2, which could lower the apparent activation energy of CO oxidation on faulted catalysts compared to that on their pristine counterparts. Our work suggests that planar defects should be considered a new and useful feature in hierarchal nanoscale design of future catalysts.

Co-adsorption of O2 and C2H4 on a Free Gold Dimer Probed via Infrared Photodissociation Spectroscopy.

Infrared multiple photon dissociation (IR-MPD) spectroscopy in conjunction with density functional theory (DFT) calculations has been employed to study the activation of molecular oxygen and ethylene co-adsorbed on a free gold dimer cation Au2+. Both studied complexes, Au2O2(C2H4)+ and Au2O2(C2H4)2+, show distinct features of both intact O2 and ethylene co-adsorbed on the cluster. However, the ethylene C=C double bond is activated, increasing in length by up to 0.07Å compared with the free molecule, and the red shift of the O-O vibration frequency increases with the number of adsorbed ethylene molecules, indicating a small but increasing activation of the O-O bond. The small O2 activation and the rather weak interaction between O2 and C2H4 are also reflected in the calculated electronic structure of the co-adsorption complexes which shows only a small occupation of the empty anti-bonding O2 2π*2p orbital as well as the localization of most of the Kohn-Sham orbitals on O2 and C2H4, respectively, with only limited mixing between O2 and C2H4 orbitals. The results are compared with theoretical studies on neutral AuxO2(C2H4) (x = 3, 5, 7, 9) complexes.

Catalytic Mechanism of CO Oxidation on Three‐Silicon‐Doped Hexagonal Boron Nitride

AbstractDoped nanomaterials show extremely high atom efficiency, low cost, high stability and activity for CO oxidation, bridging the gap between homogeneous and heterogeneous catalysis. The catalytic mechanism of CO oxidation on three‐silicon‐doped h‐BN is reported. The adsorption of O2 is more advantageous than CO. The electron transfer from the dopant activates the adsorbed O2 and initiates the following CO oxidation. The oxidation process includes O2 adsorption, electron transfer, CO adsorption, oxygen transfer, and CO2 desorption. The energy barriers for the generation of two CO2 molecules in N vacancy dopant are 0.50 and 0.33 eV, respectively. The enhanced catalytic performance indicates that three‐silicon‐doped h‐BN has potential applications to fabricate low cost and high activity BN‐based metal‐free catalysts.

Enhanced catalytic CO oxidation by Cu13-mNim (m = 0, 1, 13) clusters at ambient temperatures with more active sites and distinct mechanistic pathways

Nowadays, developing highly efficient, stable and low cost catalysts is generally considered to be the key to solve the drastically increasing of carbon monoxide (CO) emission. In this paper, Cu13-mNim (m = 0, 1, 13) bimetallic clusters have been proposed as new cluster catalysts, and their electronic, chemical properties and CO catalytic oxidation reaction are systematically calculated by DFT theoretical simulation. When an O2 molecule is adsorbed on the active-site of Cu13-mNim cluster, O2 molecule decomposing reaction occurs firstly, rather than coadsorption of O2 and CO molecule, which is modified the traditional Langmuir - Hinshelwood (LH) mechanism. By analyzing the reaction energy barrier of each step on Cu13-mNim clusters, the rate - determining step is determined as the oxidation reaction between a dissociated oxygen atom and carbon monoxide, which is hindered by a significant activation barrier. In addition, microkinetics simulations predict that Cu12Ni cluster is extremely efficient in catalyzing CO oxidation. Our findings present a rational way for designing heterogeneous catalysts with abundant reactive sites.

Co-adsorption of O2 and H2O on α-uranium (110) surface: A density functional theory study**Project supported by the National Nature Science Foundation of China (Grant Nos. 51401237, 11474358, and 51271198).

First-principles calculations based on density functional theory corrected by Hubbard parameter U (DFT+U) are applied to the study on the co-adsorption of O2 and H2O molecules to α-U(110) surface. The calculation results show that DFT+U method with Ueff = 1.5 eV can yield the experimental results of lattice constant and elastic modulus of α-uranium bulk well. Of all 7 low index surfaces of α-uranium, the (001) surface is the most stable with lowest surface energy while the (110) surface possesses the strongest activity with the highest surface energy. The adsorptions of O2 and H2O molecules are investigated separated. The O2 dissociates spontaneously in all initial configurations. For the adsorption of H2O molecule, both molecular and dissociative adsorptionsoccur. Through calculations of co-adsorption, it can be confirmed that the inhibition effect of O2 on the corrosion of uranium by water vapor originates from the preferential adsorption mechanism, while the consumption of H atoms by O atoms exerted little influence on the corrosion of uranium.

CO oxidation on Ni doped and Ni-M (M = Ca, Sc, V, Cu) bimetal-doped graphene: A first-principles study

CO oxidation over atomic Ni doped and Ni-M (M = Ca, Sc, V, Cu) bimetal-doped graphene (Ni@graphene and Ni-M@graphene, respectively) were investigated by first-principles method. For atomic Ni@graphene, O2 is adsorbed first and then reacts with CO (gas phase) directly to release the first CO2. The barrier is about 0.432 eV. The remaining O atom would react with CO (gas phase) directly and release the second CO2 with a barrier of 0.368 eV. If another metal atom was doped at the opposite site of Ni atom, the reaction path does not change. However, the calculated reaction barriers are all higher for the first CO2 release but lower for the second. The CO and O2 co-adsorption structures are all energetically unfavorable. The reason is that the LUMO orbital of the O2 pre-adsorbed structure is mainly located on the two O atoms, and thus will have a maximum overlap with the CO HOMO orbital. D-band model can explain the different adsorption energies for CO and O2.