Photocatalytic nitrogen fixation represents a green alternative to the conventional Haber–Bosch process in the conversion of nitrogen to ammonia. In this study, a series of Bi5O7Br nanostructures w...

Visible-Light-Driven Nitrogen Fixation Catalyzed by Bi5O7Br Nanostructures: Enhanced Performance by Oxygen Vacancies.

Metal-organic frameworks (MOFs) have recently emerged as promising precursors to construct efficient non-noble metal electrocatalyst for oxygen evolution reaction (OER) Herein, a Co-Ni-Fe spinel oxide-carbonitrides hybrids (CoNiFeOx-NC) electrocatalyst with hierarchical structure was synthesized from Fe-MIL-101-NH2 through a unique ion-exchange based strategy The ion exchange of Fe-MIL-101-NH2 with both Ni and Co ions induced a hierarchically structured 2-D ternary metal MOF shell layer encapsulated 3-D octahedral MOF crystals as a core This prevents the collapse of MOF frameworks during the air calcination process and affords highly porous structure and large surface area Additionally, the unique combination of Co-Ni-Fe in spinel oxides derived from calcination of the hierarchically structured core-shell MOF provides a favorable electronic environment for the adsorption of OER intermediates, which was further verified by the XPS characterizations and DFT calculations DFT study revealed the Ni-Co coordinated Oh sites in the MFe2O4 reverse spinel structures as the main active sites, which tuned the binding strength of oxygen species with a catalyst through electron transfer of Fe→Co→Ni, thereby lowered the energy barriers for OER As a result, the rationally designed CoNiFeOx-NC catalyst manifests superior OER performance with a low overpotential of 265 mV at 50 mA cm−2 and a decent Tafel slope of 641 mV dec-1 The ion-exchange based strategy may serve as a versatile platform for rational design and synthesis of multi-metallic MOF derived electrocatalysts

Hierarchical trimetallic Co-Ni-Fe oxides derived from core-shell structured metal-organic frameworks for highly efficient oxygen evolution reaction

During dry reforming of methane, oxygen species over the catalyst surface play an important role in CH4/CO2 reactivity, catalytic performance and carbon deposition. Herein, the effects of the surface adsorbed oxygen species tuned by doping with different rare-metal metals (such as Ce, La, Sm and Y) on the catalytic behavior were elaborated systematically. It was found that Y-doped catalyst exhibited the most amount of surface adsorbed oxygen species, followed by Sm, La, Ce and non-doped catalysts. The results confirmed that the surface adsorbed oxygen species were remarkably beneficial to enhance both CO2 activation and CH4 dissociation. Nevertheless, carbon formation and removal did not keep pace at low temperature due to more promotional effects of the surface adsorbed oxygen species on CH4 dissociation than CO2 activation. The gap between carbon deposition and removal was potential to be ameliorated through the accelerated activation to CO2 at high temperature.

Effects of the surface adsorbed oxygen species tuned by rare-earth metal doping on dry reforming of methane over Ni/ZrO2 catalyst

Biogas Reforming to Syngas: A Review.

Alkanes are the major constituents of natural gas and crude oil, the feedstocks for the chemical industry. The efficient and selective activation of C–H bonds can convert abundant and low-cost hydrocarbon feedstocks into value-added products. Due to the increasing global demand for light alkenes and their corresponding polymers as well as synthesis gas and hydrogen production, C–H bond activation of light alkanes has attracted widespread attention. A theoretical understanding of C–H bond activation in light hydrocarbons via density functional theory (DFT) and microkinetic modeling provides a feasible approach to gain insight into the process and guidelines for designing more efficient catalysts to promote light alkane transformation. This review describes the recent progress in computational catalysis that has addressed the C–H bond activation of light alkanes. We start with direct and oxidative C–H bond activation of methane, with emphasis placed on kinetic and mechanistic insights obtained from DFT assisted microkinetic analysis into steam and dry reforming, and the partial oxidation dependence on metal/oxide surfaces and nanoparticle size. Direct and oxidative activation of the C–H bond of ethane and propane on various metal and oxide surfaces are subsequently reviewed, including the elucidation of active sites, intriguing mechanisms, microkinetic modeling, and electronic features of the ethane and propane conversion processes with a focus on suppressing the side reaction and coke formation. The main target of this review is to give fundamental insight into C–H bond activation of light alkanes, which can provide useful guidance for the optimization of catalysts in future research.

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C-H bond activation in light alkanes: a theoretical perspective.

Modulating lattice oxygen in metal oxides that conducts partial oxidation of methane in balancing C-H activation and syngas selectivity remains challenging. This paper describes the discovery of distorting FeO6 octahedra in La1-xCexFeO3 (x = 0, 0.25 0.5, 0.75, 1) orthorhombic perovskites for the promotion of lattice oxygen activation. By combined electrical conductivity relaxation measurements and density functional theory calculations studies, this paper describes the enhancement of FeO6 octahedral distortion in La1-xCexFeO3 promoting their bulk oxygen mobility and surface oxygen exchange capability. Consequently, La0.5Ce0.5FeO3 with the highest FeO6 distortion achieves exceptional syngas productivity of ∼3 and 8 times higher than LaFeO3 and CeFeO3, respectively, in CH4 partial oxidation step with simultaneous high CO2 conversion (92%) in the CO2-splitting step at 850 °C. The results exemplify the feasibility to tailor the active lattice oxygen of perovskite by modulating the distortion of BO6 in ABO3, which ultimately influences their reaction performance in chemical looping processes.

FeO6 Octahedral Distortion Activates Lattice Oxygen in Perovskite Ferrite for Methane Partial Oxidation Coupled with CO2 Splitting.

The modulation of the interaction between the active metal and the underlying support material plays a key role and remains a challenge in many important catalytic reactions. This paper describes a new method for the modification of Ni/Al2O3 by La2O2CO3, which is responsible for modulating the interaction between Ni and the Al2O3 support. When La2O2CO3 is loaded on the Al2O3 support as a La2O3 precursor, combined with XRD, H2-TPR, H2-pluse chemisorption, Raman spectroscopy and TEM characterization, it is found that La2O2CO3 can prevent Ni from entering the alumina support and forming NiAl2O4. This strategy allows more Ni to be reduced and exposed as active sites. Consequently, the La2O2CO3 modified Ni/Al2O3 exhibited superior activity with respect to the reference La2O3 modified Ni/Al2O3 and original Ni/Al2O3 in dry reforming of methane (DRM). At the same time, La can cover the acidic sites of alumina and increase the alkalinity of the catalyst, thereby promoting carbon dioxide adsorption and activation, and inhibiting carbon deposition. In addition, the introduction of La also inhibits the sintering of Ni under harsh reaction conditions by enhancing the interaction between Ni metal and the support. This modification method can simultaneously improve the reactivity and stability of the catalyst by altering the interaction between the metal and the support.

Dry reforming of methane over La2O2CO3-modified Ni/Al2O3 catalysts with moderate metal support interaction

This paper describes the synthesis of ordered mesoporous Ni/La2O3 catalysts (denoted as Ni/La2O3-m) for dry reforming of methane and investigates the synergistic effect of Ni/La2O3 interfaces on the activation of CO2. The resultant nanostructured La2O3 possessed high specific surface area of 211.5 m2/g, and Ni/La2O3-m catalysts maintained the initial morphology upon thermal treatment. The mesostructure was beneﬁcial to obtain and maintain Ni nanoparticles with sizes between 4–6 nm. Ni/La2O3-m catalysts exhibited superior activity and stability in dry reforming of methane, showing excellent performance in activating both CH4 and CO2 due to more catalytically active Ni sites and increased interfaces. In situ DRIFTS indicated that bidentate carbonate participates in coke elimination. Combined with CO2-TPD and density functional theory (DFT) calculations, we found that Ni/La2O3-m catalyst has stronger capability to promote the formation of bidentate carbonate due to the increased interfaces by enhancing Ni dispersion, which leads to better stability by suppressing the coke deposition.

Ordered mesoporous Ni/La2O3 catalysts with interfacial synergism towards CO2 activation in dry reforming of methane

Auto-thermal reforming of methanol is an attractive route for low-temperature methanol conversion for hydrogen production. This paper describes utilization the lattice oxygen of Cu2O/Ca2Fe2O5 participates the partial oxidation of methanol to achieve the efficient auto-thermal reforming of methanol. ASPEN Plus software was adopted to verify the feasibility of auto-thermal conversion of methanol via Cu↔Cu2O looping and provided a comprehensive understanding of the associated process via operating parameter optimization. A series of CuO/Ca2Fe2O5 with different contents of copper were prepared as the catalytic oxygen carrier (COC) which goes through the reduction → catalytic methanol conversion →re-oxidation. The surface and bulk properties of COCs were characterized by XRD, XPS, TEM-EDS mapping, Raman, and H2-TPR; the reaction pathways were investigated using CH3OH-pulse and in situ DRIFTS. Results indicate that 40 % Cu-loaded Cu2O-Ca2Fe2O5 shows the highest catalytic activity of the synthesized COCs, and the presence of Ca2Fe2O5 tunes the redox activity and mobility of the lattice oxygen, obtaining a H2 production rate of 37.6 μmol·H2∙g−1·COC·s−1 at 240 °C. The reaction pathways of chemical looping methanol conversion follow the sequence: CH3OH full oxidation → formaldehyde intermediate → methyl-formate intermediate as the amount of lattice oxygen decreases gradually.

Xianhua Zhang

Papers

FeO6 Octahedral Distortion Activates Lattice Oxygen in Perovskite Ferrite for Methane Partial Oxidation Coupled with CO2 Splitting.

Dry reforming of methane over La2O2CO3-modified Ni/Al2O3 catalysts with moderate metal support interaction

Ordered mesoporous Ni/La2O3 catalysts with interfacial synergism towards CO2 activation in dry reforming of methane

Chemical looping oxidative steam reforming of methanol: A new pathway for auto-thermal conversion

Chemical looping steam reforming of methane over Ce-doped perovskites