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Direct methane conversion (DMC) to oxygenates at low temperature is of great value but remains challenging due to the high energy barrier for C−H bond activation. Here, we report that in situ decoration of Pd1‐ZSM‐5 single atom catalyst (SAC) by CO molecules significantly promoted the DMC reaction, giving the highest turnover frequency of 207 h−1 ever reported at room temperature and ~100 % oxygenates selectivity with H2O2 as oxidant. Combined characterizations and DFT calculations illustrate that the C‐atom of CO prefers to coordinate with Pd1, which donates electrons to the Pd1−O active center (L−Pd1−O, L=CO) generated by H2O2 oxidation. The correspondingly improved electron density over Pd−O pair renders a favorable heterolytic dissociation of C−H bond with low energy barrier of 0.48 eV. Applying CO decoration strategy to M1‐ZSM‐5 (M=Pd, Rh, Ru, Fe) enables improvement of oxygenates productivity by 3.2–11.3 times, highlighting the generalizability of this method in tuning metal‐oxo electronic structure of SACs for efficient DMC process. [ABSTRACT FROM AUTHOR]

Chemical looping reforming of methane to syngas (CO and H2) is one of the most promising routes for methane utilization, where the further reaction of CO on oxygen carrier surfaces is a primary determinant of CO selectivity. In this work, the effects of oxygen vacancy (Vo) on CO desorption, CO oxidation, and CO dissociation are systematically studied by using density functional theory calculattions. Our calculated results reveal that increasing Vo concentration can weaken CO desorption at Fe sites due to the enhanced localization of electrons in the Fe atoms. Also, the increase in Vo concentration from 1/12 ML to 1/6 ML leads to a dramatic increase of activation energy in the CO oxidation from 0.64 eV to 1.10 eV. Moreover, the increase in Vo concentration is conducive to CO dissociation, but the dissociation is still almost impossible due to the high reaction energies (large than 3.00 eV). Considering these three reaction paths, CO desorption can proceed spontaneously at reaction temperatures above 900 K. Increasing Vo concentration can improve the selectivity of syngas production due to the less favorable CO oxidation compared with CO desorption at high Vo concentrations (1/6 ML). This work reveals the microscopic mechanism that CO selectivity rises in the CLRM as the degree of Fe2O3 reduction increases. [ABSTRACT FROM AUTHOR]

The development of a single-atom iron catalyst (Fe©SiO2) for the direct conversion of methane to olefins, aromatics, and hydrogen is a breakthrough in the field of nonoxidative conversion of methane (NCM). However, the optimization of the catalyst remains desirable for industrial applications. Herein, 25 transition metals, including Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, and Au, are selected to replace the central Fe atom for screening out better single-atom catalysts for the NCM. Using the performance on the activation of methane, such as the adsorption energy of methane, the dissociation energy, and the barrier of methane as the screening descriptors, Mn©SiO2, Fe©SiO2, W©SiO2, and Re©SiO2 are first screened out. The remarkable performance of the four catalysts on methane activation is attributed to the unique geometric structure and the d z 2 orbitals of the central metal crossing over the Fermi level, which can benefit the interaction between methane and the catalysts. By considering the catalytic performance on the whole pathway of methane to ethylene, W©SiO2 is finally selected as the most active catalyst for the NCM, which has the lowest rate-determining barrier of 1.62 eV and the smallest free energy span (1.06 eV) of the overall catalytic cycle. [ABSTRACT FROM AUTHOR]

Methane (CH4) oxidation to high value chemicals under mild conditions through photocatalysis is a sustainable and appealing pathway, nevertheless confronting the critical issues regarding both conversion and selectivity. Herein, under visible irradiation (420 nm), the synergy of palladium (Pd) atom cocatalyst and oxygen vacancies (OVs) on In2O3 nanorods enables superior photocatalytic CH4 activation by O2. The optimized catalyst reaches ca. 100 μmol h−1 of C1 oxygenates, with a selectivity of primary products (CH3OH and CH3OOH) up to 82.5%. Mechanism investigation elucidates that such superior photocatalysis is induced by the dedicated function of Pd single atoms and oxygen vacancies on boosting hole and electron transfer, respectively. O2 is proven to be the only oxygen source for CH3OH production, while H2O acts as the promoter for efficient CH4 activation through ·OH production and facilitates product desorption as indicated by DFT modeling. This work thus provides new understandings on simultaneous regulation of both activity and selectivity by the synergy of single atom cocatalysts and oxygen vacancies. CH4 oxidation to high value chemicals under mild conditions through photocatalysis confronts critical issues regarding both conversion and selectivity. Here, atomic Pd and oxygen vacancies were integrated on In2O3 nanorods, leading to visible-driven CH4 conversion with a remarkable yield of oxygenates and high selectivity of primary products. [ABSTRACT FROM AUTHOR]

The direct, nonoxidative conversion of methane on a silica‐confined single‐atom iron catalyst is a landmark discovery in catalysis, but the proposed gas‐phase reaction mechanism is still open to discussion. Here, we report a surface reaction mechanism by computational modeling and simulations. The activation of methane occurs at the single iron site, whereas the dissociated methyl disfavors desorption into gas phase under the reactive conditions. In contrast, the dissociated methyl prefers transferring to adjacent carbon sites of the active center (Fe1©SiC2), followed by C−C coupling and hydrogen transfer to produce the main product (ethylene) via a key −CH−CH2 intermediate. We find a quasi Mars–van Krevelen (quasi‐MvK) surface reaction mechanism involving extracting and refilling the surface carbon atoms for the nonoxidative conversion of methane on Fe1©SiO2 and this surface process is identified to be more plausible than the alternative gas‐phase reaction mechanism. [ABSTRACT FROM AUTHOR]

[Display omitted] • A series of SA-FLP dual-active-site catalysts are designed for the conversion of CH 4 and CO 2 to acetic acid. • The SA-FLP dual active sites can concurrently adsorb and activate CH 4 and CO 2. • Ag 1 -FLP catalyst exhibits the best performance in the reaction of CH 4 and CO 2 to acetic acid. Direct conversion of CH 4 and CO 2 into acetic acid is an emerging attractive process but remains a significant challenge due to the inherent stability of both molecules. Hence, developing active and stable catalysts is crucial for the simultaneous activation of CO 2 and CH 4. Herein, we designed the "Single-Atom" - "Frustrated-Lewis-Pair" (SA-FLP) dual-active-site catalysts for the co-conversion of CH 4 and CO 2 to acetic acid based on density functional theory (DFT) calculations. The SA sites were introduced by doping the transition-metal (TM) atoms (TM = Fe, Co, Ni, Cu; Ru, Rh, Pd, Ag; Os, Ir, Pt, Au) into CeO 2 (1 1 0) surface, and the FLP sites were constructed by the regulation of surface oxygen vacancies. Our results demonstrate the introduction of SA into CeO 2 surface could facilitate the formation of oxygen vacancies, and thus promotes the formation of FLP sites. The SA-FLP dual active sites can concurrently activate CH 4 and CO 2 with CH 4 preferentially activated at SA sites and CO 2 preferentially activated at FLP sites. Among the twelve SA-FLP catalysts, Ag 1 -FLP catalyst exhibits the best performance in the reaction of CH 4 and CO 2 to acetic acid with a rate-determining barrier of 1.12 eV and a turnover frequency of 2.52 × 10–3 s−1 at 573 K and 2 bar. This work not only offers a novel catalyst prototype for the co-conversion of CH 4 and CO 2 to acetic acid but also provides insights into developing dual-active-site catalysts on earth-abundant metal oxide materials. [ABSTRACT FROM AUTHOR]

• A microkinetic model combining oxygen supply and catalysis was established for Fe 2 O 3. • The influence of TMs-doping in Fe 2 O 3 on oxygen carriers was systematically studied. • Ni-doping in Fe 2 O 3 has been confirmed to enhance the formation rate and the selectivity of CO. The rate-matching between oxygen migration and surface catalytic reaction of oxygen carrier (OC) is a critical determinant for the reaction selectivity of the chemical looping reforming (CLR) of methane. However, the theoretical mechanism behind this rate-matching relationship is still unclear. Herein, we propose to use density functional theory (DFT) combined with microkinetic simulations to establish a model integrating the methane oxidation reactions with oxygen migration kinetics on α-Fe 2 O 3 oxygen carrier. Our calculated results reveal that the transition metals (TMs)-doping such as Co, Ni, and Cu after Fe element in the periodic table can accelerate the oxygen migration rate as it promotes the upshift of the O p -band center. Moreover, a suitable oxygen migration energy barrier of about 1.0 eV is helpful to enhance the harmonization of α-Fe 2 O 3 oxygen migration and surface catalytic reactions. Based on this, Ni-doping in α-Fe 2 O 3 is predicted to be able to enhance the oxygen migration rate to match the rate of first-step methane dissociation, thereby simultaneously improving the reaction rate and the selectivity in the CLR of methane to syngas. These results could help to understand the relationship between oxygen migration and surface catalytic reaction rates and pave the way for the rational design of metal oxide oxygen carriers. [ABSTRACT FROM AUTHOR]

[Display omitted] • The oxygen migration properties of Fe 2 O 3 (oxygen carrier) were systematically investigated. • The matching problem of oxygen migration rate with the surface catalytic reaction rate was studied. • A suitable concentration of oxygen vacancies is found to be beneficial for the chemical looping reforming of methane to syngas. The chemical looping reforming of methane to syngas is of great significance to the sustainable development of energy and environment, where the oxygen carrier (OC) is the core element of this technology. To study the oxygen migration properties of OCs and the matching problem of oxygen migration rate with the surface catalytic reaction rate, we present a theoretical study by taking the abundant and cheap α-Fe 2 O 3 as the model OC. It is found that the migration rate of lattice oxygen and the dissociation of methane will be enhanced as the concentration of surface oxygen vacancy increases. By comparing the oxygen migration rate with the methane dissociation rate, we reveal that the two rates can match well at a low surface oxygen vacancy concentration, which is the key to the selective production of syngas. Lower or higher surface oxygen vacancy concentration will lead to the products towards carbon dioxide or coke. [ABSTRACT FROM AUTHOR]