Low-temperature water–gas shift reaction over cobalt–molybdenum carbide catalyst

Boosting reactivity of water-gas shift reaction by synergistic function over CeO2-x/CoO1-x/Co dual interfacial structures

Dual-interfacial structure within catalysts is capable of mitigating the detrimentally completive adsorption during the catalysis process, but its construction strategy and mechanism understanding remain vastly lacking. Here, a highly active dual-interfaces of CeO2-x/CoO1-x/Co is constructed using the pronounced interfacial interaction from surrounding small CeO2-x islets, which shows high activity in catalyzing the water-gas shift reaction. Kinetic evidence and in-situ characterization results revealed that CeO2-x modulates the oxidized state of Co species and consequently generates the dual active CeO2-x/CoO1-x/Co interface during the WGS reaction. A synergistic redox mechanism comprised of independent contribution from dual functional interfaces, including CeO2-x/CoO1-x and CoO1-x/Co, is authenticated by experimental and theoretical results, where the CeO2-x/CoO1-x interface alleviates the CO poison effect, and the CoO1-x/Co interface promotes the H2 formation. The results may provide guidance for fabricating dual-interfacial structures within catalysts and shed light on the mechanism over multi-component catalyst systems.

Carbon Dioxide Conversion on Supported Metal Nanoparticles: A Brief Review

The increasing concentration of anthropogenic CO2 in the air is one of the main causes of global warming. The Paris Agreement at COP 21 aims to reach the global peak of greenhouse gas emissions in the second half of this century, with CO2 conversion towards valuable added compounds being one of the main strategies, especially in the field of heterogeneous catalysis. In the current search for new catalysts, the deposition of metallic nanoparticles (NPs) supported on metal oxides and metal carbide surfaces paves the way to new catalytic solutions. This review provides a comprehensive description and analysis of the relevant literature on the utilization of metal-supported NPs as catalysts for CO2 conversion to useful chemicals and propose that the next catalysts generation can be led by single-metal-atom deposition, since in general, small metal particles enhance the catalytic activity. Among the range of potential indicators of catalytic activity and selectivity, the relevance of NPs’ size, the strong metal–support interactions, and the formation of vacancies on the support are exhaustively discussed from experimental and computational perspective.

A Single Source, Scalable Route for Direct Isolation of Earth-Abundant Nanometal Carbide Water-Splitting Electrocatalysts

Single-phase M_xCs (M = Fe, Co, and Ni) were prepared by solvothermal conversion of Prussian blue single source precursors. The single source precursor is prepared in water, and the conversion process is carried out in alkylamines at reaction temperatures above 200 °C. The reaction is scalable using a commercial source of Fe-PB. High-resolution transmission electron microscopy, X-ray photoelectron microscopy, and powder X-ray diffraction confirm that carbides have thin oxide termination but lack graphitic surfaces. Electrocatalytic activity reveals that Fe₃C and Co₂C are oxygen evolution reaction electrocatalysts, while Ni₃C is a bifunctional [OER and hydrogen evolution reaction (HER)] electrocatalyst.

On Catalytic Behavior of Bulk Mo2C in the Hydrodenitrogenation of Indole over a Wide Range of Conversion Thereof

The catalytic activity of bulk molybdenum carbide (Mo2C) in the hydrodenitrogenation (HDN) of indole was studied. The catalyst was synthesized using a temperature-programmed reaction of the respective oxide precursor (MoO3) with the carburizing gas mixture of 10 vol.\% CH4/H2. The resultant material was characterized using X-ray diffraction, CO chemisorption, and nitrogen adsorption. The catalytic activity was studied in the HDN of indole over a wide range of conversion thereof and in the presence of a low amount of sulfur (50 ppm), which was used to simulate the processing of real petroleum intermediates. The molybdenum carbide has shown high activity under the tested operating conditions. Apparently, the bulk molybdenum carbide turned out to be selective towards the formation of aromatic products such as ethylbenzene, toluene, and benzene. The main products of HDN were ethylbenzene and ethylcyclohexane. After 99% conversion of indole HDN was reached (i.e., lack of N-containing compounds in the products was observed), the hydrogenation of ethylbenzene to ethylcyclohexane took place. Thus, the catalytic behavior of bulk molybdenum carbide for the HDN of indole is completely different compared to previously studied sulfide-based systems.

High Temperature Water Gas Shift Reactivity of Novel Perovskite Catalysts

High temperature water-gas shift (HT-WGS) is an industrially highly relevant reaction. Moreover, climate change and the resulting necessary search for sustainable energy sources are making WGS and reverse-WGS catalytic key reactions for synthetic fuel production. Hence, extensive research has been done to develop improved or novel catalysts. An extremely promising material class for novel highly active HT-WGS catalysts with superior thermal stability are perovskite-type oxides. With their large compositional flexibility, they enable new options for rational catalyst design. Particularly, both cation sites (A and B in ABO3) can be doped with promoters or catalytically active elements. Additionally, B-site dopants are able to migrate to the surface under reducing conditions (a process called exsolution), forming catalytically active nanoparticles and creating an interface that can strongly boost catalytic performance. In this study, we varied A-site composition and B-site doping (Ni, Co), thus comparing six novel perovskites and testing them for their HT-WGS activity: La0.9Ca0.1FeO3-δ, La0.6Ca0.4FeO3-δ, Nd0.9Ca0.1FeO3-δ, Nd0.6Ca0.4FeO3-δ, Nd0.6Ca0.4Fe0.9Ni0.1O3-δ and Nd0.6Ca0.4Fe0.9Co0.1O3-δ. Cobalt and Nickel doping resulted in the highest activity observed in our study, highlighting that doped perovskites are promising novel HT-WGS catalysts. The effect of the compositional variations is discussed considering the kinetics of the two partial reactions of WGS-CO oxidation and water splitting.

Magnetic and electronic properties of single-walled Mo2C nanotube: a first-principles study

The structural, electronic, and magnetic properties of single-walled Mo₂C nanotubes are investigated by using first-principles calculations. We establish that single-walled Mo₂C nanotubes can be rolled up from a graphene-like Mo₂C monolayer with H- or T-type phase, i.e. H-Mo₂C and T-Mo₂C nanotubes. The armchair-type T-Mo₂C nanotubes are more energetically stable than H-Mo₂C nanotubes with the same diameter, while zigzag-type H-Mo₂C nanotubes are more energetically stable than T-Mo₂C nanotubes. In particular, (8, 0) H-Mo₂C nanotube are more stable than Mo₂C monolayer due to structural deformation. All Mo₂C nanotubes are magnetic metals, independent of their chirality, and the magnetic moments of Mo atoms in the outer layer are larger than the inner. The ionic and metallic bonds in Mo₂C nanotubes and delocalized electrons around Mo atoms lead to the versatile electronic and magnetic properties in them, endowing them potential applications in catalysts and electronics.

Reactions of water and C1 molecules on carbide and metal-modified carbide surfaces

The formation of carbides can significantly modify the physical and chemical properties of the parent metals. In the current review, we summarize the general trends in the reactions of water and C1 molecules over transition metal carbide (TMC) and metal-modified TMC surfaces and thin films. Although the primary focus of the current review is on the theoretical and experimental studies of reactions of C1 molecules (CO, CO₂, CH₃OH, etc.), the reactions of water will also be reviewed because water plays an important role in many of the C1 transformation reactions. This review is organized by discussing separately thermal reactions and electrochemical reactions, which provides insights into the application of TMCs in heterogeneous catalysis and electrocatalysis, respectively. In thermal reactions, we discuss the thermal decomposition of water and methanol, as well as the reactions of CO and CO₂ over TMC surfaces. In electrochemical reactions, we summarize recent studies in the hydrogen evolution reaction, electrooxidation of methanol and CO, and electroreduction of CO₂. Finally, future research opportunities and challenges associated with using TMCs as catalysts and electrocatalysts are also discussed.

Simple and large-scale synthesis of β-phase molybdenum carbides as highly stable catalysts for dry reforming of methane

The catalytic stability of monometallic β-Mo₂C/CNTs was found to be superior to that of bimetallic Ni/β-Mo₂C under similar reaction conditions.

Oxidation of the hexagonal Mo2C(101) surface by H2O dissociative adsorption

Oxidation of the hexagonal Mo₂C(101) surface by H₂O dissociative adsorption was investigated using periodic density functional theory.

Elucidating the role of oxygen coverage in CO2 reduction on Mo2C

Revealed linear relationships between oxygen coverage and electronic modification of the Mo₂C catalyst that tunes the reactivity for CO₂ reduction.

Simple synthesis of ultrasmall β-Mo2C and α-MoC1−x nanoparticles and new insights into their catalytic mechanisms for dry reforming of methane

Ultrasmall β- and α-molybdenum carbide particles were synthesized by a resin route and they showed different oxidation–recarburization cycles.

One-step synthesis of bulk Mo and Ni–Mo carbides for methanation

β-Mo₂C and Ni/β-Mo₂C catalysts were prepared by a single-step thermal decomposition method using hexamethylentetramine (HMT) as a reducing agent and carbon source.

Transition metal promoted K/Mo2C as efficient catalysts for CO hydrogenation to higher alcohols

The transition metals strongly interact with molybdenum, forming mixed carbidic phases, that are likely responsible for the enhanced higher alcohol formation. These phases serve as active sites for molecular rather than dissociative adsorption of CO and offer a balance of non-dissociated and dissociated CO species on the surface.

Coverage dependent adsorption and co-adsorption of CO and H2 on the CdI2-antitype metallic Mo2C(001) surface

The adsorption and co-adsorption of CO and H₂ at different coverage on the CdI₂-antitype metallic Mo₂C(001) surface termination have been systematically computed at the level of periodic density functional theory.

Effect of sulphidation temperature on the performance of NiO–MoO3/γ-Al2O3 catalysts for sulphur-resistant methanation

Sulphidation temperature has a pronounced influence on both textural and structural properties of NiO–MoO₃/γ-Al₂O₃ catalysts for sulphur-resistant methanation.