Molybdenum carbide nanoparticle: Understanding the surface properties and reaction mechanism for energy production towards a sustainable future
Introduction
One of the most important research gaps in the field of renewable and sustainable energy is rational design and synthesis of suitable eco-friendly and cost-effective catalysts with preserved energy and chemical functionality for prolonged applications in several industrial processes [1], [2], [3]. The unique chemical and physical properties of molybdenum carbide nanoparticle [4] have enhanced its popularity in the fields of materials and chemical science towards production of renewable and sustainable energy [5]. The outstanding properties of MCN include thermal stability, high electrical conductivity, adsorption capacity, high melting point, and hardness [6]. Moreover, the characteristics of MCNs such as resistance to nitrogen and sulfur, high catalytic current density, and durability are similar to those of noble metals, which enable their utilization in hydrogenation and hydrogen evolution reactions (HER) [7], [8]. Examples of these reactions include CO2 hydrogenation to alcohol, CO hydrogenation to alcohol [9], hydrodeoxygenation [10], electrocatalytic hydrogen evolution from water splitting [11] including oxygen evolution reaction [12], hydro-treating [13], watergas shift reaction (WGS) [14], hydrodesulfurization (HDS) [15], CH4 aromatization [16], and hydrodenitrogenation (HDN) [17]. The MCNs are also suitable for electrocatalytic reactions.
MCN has been used successfully to hydrogenate feedstock such as cellulose, indole, toluene, and cumene, which are popularly processed with group 9 and 10 noble metals (Pt, Pd, Rh) [18], [19], [20]. These being commercially available catalysts for reactions such as methane reforming, hydrocarbon isomerization, water-gas shift reactions, and CO hydrogenation. Further, MCN has been employed as an alternative to Ru, and to an extent Pt as electrocatalysts in the anode of polymer membrane fuel cells (PEMFC) [21], [22], [23] because of its platinum-like behaviors [24]. The thermal stability of MCN in the absence of oxygen is due to the delay of the sintering and attrition effects as reaction proceeds. However, the catalytic activity of MCN systems mainly depends on the nature and physiochemical properties of the catalyst.
Previously, the high temperature classical metallurgical process was used to prepare metal carbides but the products exhibit low specific surface areas and high particle size [25]. This results in the Metal carbide products exhibiting low catalytic performance in targeted catalytic processes [3]. Currently, the MCN synthesis method by Lee et al. [26], which is a temperature program reduction (TPR) carburization is most popular due to its remarkable improvement on the textural property of the product [27]. TPR carburization is a carbothermal reduction method that carburizes the Mo precursor supported on carbon in hydrogen atmosphere [28]. The Mo precursor is to be thermally treated, at increasing the controlled temperature in a reducing environment [29]. To form the carbide phase, the carbon source is mainly light hydrocarbon, while hydrogen is the reducing agent. The essence of the controlled temperature is to optimize the carburation temperature to avoid sintering of the reduced Mo particles, thereby reducing the particle size of the resulting carbide. The carburization conditions (temperature and time) control the physiochemical properties, the chemical nature, and structure of the resulting carbide phase. MCN exists in two main crystalline structures: orthorhombic and hexagonal (Mo2C) and hexagonal structure. The preparation methods of carbide-supported metal catalysts include wet impregnation [30], atomic layer deposition [31] and vacuum environment [32]. Mostly, the synthesized MCN, passivated prior to its exposure to air to prevent oxidation.
The goal of this review is to provide insight into the surface properties of MCN and its reaction mechanism for renewable and sustainable energy production towards a sustainable future. In Section 2, rational design and synthesis of MCN are discussed, highlighting the effect of operating parameters. The third section deals with a structural diversity of MCN using density functional theory (DFT) to categorize different form of MCN based on structural differences. Section 4 briefly discusses the surface properties of MCNs to determine the stability based on their structural diversity. While Section 5 gives an insight into multiscale reaction model on MCNs for a better understanding of catalytic reaction mechanism of the system, which is crucial to the commercial applications of MCN in the production of renewable and sustainable energy. Finally, we presented the catalytic activity of MCN based catalysts (both unsupported and promoted/supported) in Section 6.
Section snippets
Preparation of MCN
MCNs are popularly prepared by carbothermal reduction carburization process. This process consists of three different steps; (i) deposition of the Mo-precursor on the carbon source, (ii) carbothermal reduction of the Mo-precursor to produce MCN, and [33] the subsequent stabilization of the produced MCN by Mo-carbide surface passivation [19]. Generally, synthesis of MoO2 nanoparticles is not a difficult task; the transformation into MCN is where the major challenge is. The transformation is so
Structural diversity of molybdenum carbide
Understanding the structural diversity of MCN is an uphill task due to its complex nature and a number of metastable and stable phases [52]. However, density functional theory (DFT) based estimations with the revised Perdew–Burke–Ernzerhof (RPBE) exchange-correlation functional has been successfully employed to identify the crystal structure [53]. MCN is characterized by five different crystal structures: α-MoC1−x, α-Mo2C, β-Mo2C, γ-MoC and η-MoC [54], which arise from different preparation
Surface properties of MCNs
MCNs possess a similar surface to that of transition metal surface M(111), which is a little more reactive toward CH2/3 species when compared with metals with a similar strength of carbon adsorption. This makes MCN a suitable for hydrogenation reaction, which is less vulnerable to graphite poisoning because of an increased attraction to hydrocarbons [74]. Moreover, Mo2C (001) has a similar the O/OHx binding with that of the transition metal M(211) surfaces indicating the likelihood of oxygen
Multiscale reaction model on MCNs
For a better understanding of catalytic reaction mechanism with MCNs, there is a need to establish a multiscale reaction model, which combines quantum mechanical (QM) density functional tight-binding (DFTB) technique with a molecular mechanical (MM) force field [82], [83]. This could be accomplished by building a QM/MM model to define the MCN, the model aromatic solvent, and the surroundings. The free energy profiles of the reactions could be determined by using Umbrella sampling (US) [82]. Liu
Unsupported MCN
Recently, Posada-Pérez et al. [116] reported the use of MCN heterogeneously catalyzed hydrogenation reactions, where H2 is adsorbed and dissociated. The study was carried out using systemic DFT-PBE with or without dispersion terms, regarding the interaction and stability of H2 with orthorhombic β-Mo2C(001) and cubic δ-MoC(001) surfaces. For β-Mo2C(001), two likely Mo or C terminations are considered. Their report shows that the energy profiles for the elementary steps H2 dissociation are mainly
Conclusion
Definitely, hydrogenation and hydrogen production reactions are the modern research hotspot towards renewable and sustainable energy production and have, therefore, inspired extensive interests in rational design and synthesis of cheap, noble metal-free, thermal/hydrothermal stable and active catalysts. This will offer a remarkable relief to the renewable and sustainable energy community. One of such materials is MCN, which is a promising replacement for noble metals. Factors like carbon
Acknowledgments
The authors gratefully acknowledge the financial support from GSP-MOHE (MO008–2015) High Impact Research (HIR) grant and RP015–2012D grant, University of Malaya, Malaysia.
References (133)
- et al.
Hydrogenation of CO on molybdenum and cobalt molybdenum carbides
Appl Catal A: General
(2012) - et al.
New insights into high-valence state Mo in molybdenum carbide nanobelts for hydrogen evolution reaction
Int J Hydrog Energy
(2017) - et al.
Mo 2 C catalyzed vapor phase hydrodeoxygenation of lignin-derived phenolic compound mixtures to aromatics under ambient pressure
Appl Catal A: General
(2016) - et al.
Dissociation of CO and H 2 O during water–gas shift reaction on carburized Mo/Al 2 O 3 catalyst
Appl Catal A: General
(2011) - et al.
HDN and HDS of different gas oils derived from Athabasca bitumen over phosphorus-doped NiMo/γ-Al2O3 carbides
Appl Catal B: Environ
(2006) - et al.
A comparative study of the catalytic performance of Co-Mo and Co (Ni)-W carbide catalysts in the hydrodenitrogenation (HDN) reaction of pyridine
Appl Catal A: Gen
(2007) - et al.
Structural evolution of alumina supported Mo–W carbide nanoparticles synthesized by precipitation from homogeneous solution
Mater Res Bull
(2005) - et al.
On the genesis of molybdenum carbide phases during reduction-carburization reactions
J Solid State Chem
(2012) - et al.
Composites of graphene-Mo 2 C rods: highly active and stable electrocatalyst for hydrogen evolution reaction
Electrochim Acta
(2016) - et al.
Highly dispersed molybdenum carbide as non-noble electrocatalyst for PEM fuel cells: performance for CO electrooxidation
Int J Hydrog Energy
(2010)
Cyclic voltammetry and X-ray photoelectron spectroscopy studies of electrochemical stability of clean and Pt-modified tungsten and molybdenum carbide (WC and Mo 2 C) electrocatalysts
J Power Sources
Tungsten and nickel tungsten carbides as anode electrocatalysts
Electrochim Acta
Molybdenum carbide catalyst formation from precursors deposited on active carbons: XRD studies
Appl Catal A: General
Molybdenum carbide catalysts: I. Synthesis of unsupported powders
J Catal
New synthesis of Mo 2 C 14 nm in average size supported on a high specific surface area carbon material
J Solid State Chem
Metal carbides and nitrides as potential catalysts for hydroprocessing
Appl Catal A: Gen
Catalytic performances of platinum doped molybdenum carbide for simultaneous hydrodenitrogenation and hydrodesulfurization
Catal Today
Formation of β-Mo 2C below 600 °C using MoO 2 nanoparticles as precursor
J Catal
Catalysis over molybdenum carbides and nitrides: I. Catalyst characterization
J Catal
High specific surface area Mo 2C nanoparticles as an efficient electrocatalyst for hydrogen evolution
J Power Sources
Encapsulation of carbides of chromium, molybdenum and tungsten in carbon nanocapsules by arc discharge
J Cryst Growth
A study on mechanochemical behavior of MoO 3–Mg–C to synthesize molybdenum carbide
Int J Refract Met Hard Mater
Effect of carburization protocols on molybdenum carbide synthesis and study on its performance in CO hydrogenation
Catal Today
Steam reforming of methanol for hydrogen production over nanostructured wire-like molybdenum carbide catalyst
Int J Hydrog Energy
CO 2 hydrogenation on Au/TiC, Cu/TiC, and Ni/TiC catalysts: production of CO, methanol, and methane
J Catal
Study of the mechanism of formation of nano-crystalline zeolite X in heterogeneous system
Microporous Mesoporous Mater
Preparation and characterization of alumina-supported molybdenum carbide
Appl Catal A: Gen
Formation of encapsulated molybdenum carbide particles by annealing mechanically activated mixtures of amorphous carbon with molybdenum
Carbon
Benzene adsorption on Mo 2C: a theoretical and experimental study
Appl Catal A: Gen
Phase stability diagrams of transition metal carbides, a theoretical study
Chem Phys Lett
Preparation of Mo 2C single crystals by the floating zone method
J Cryst Growth
Catalyst size matters: tuning the molecular mechanism of the water–gas shift reaction on titanium carbide based compounds
J Catal
Elementary steps of syngas reactions on Mo 2C (001): adsorption thermochemistry and bond dissociation
J Catal
High resolution images of Mo 2C (0001)-(3× 3) R30° structure by scanning tunneling microscopy
Surf Sci
Photoelectron spectroscopy study of Mo 2C (0001)
Solid State Commun
Surface electronic structure of α-Mo 2C (0001)
Surf Sci
About CO and H2 activation mechanisms on Fe and Mo2C catalysts on the basis of density functional theory computation and ab initio atomistic thermodynamics
Artificial neural network study for the estimation of the C–H bond dissociation enthalpies
J Fluor Chem
Kaolinite properties and advances for solid acid and basic catalyst synthesis
RSC Adv
Efficient biodiesel production via solid superacid catalysis: a critical review on recent breakthrough
RSC Adv
Insight into catalyst deactivation mechanism and suppression techniques in thermocatalytic deoxygenation of bio-oil over zeolites
Rev Chem Eng
In-situ destruction of chlorinated hydrocarbons in groundwater using catalytic reductive dehalogenation in a reactive well: testing and operational experiences
Environ Sci Technol
Carbon nanofiber supported transition‐metal carbide catalysts for the Hydrodeoxygenation of Guaiacol
ChemCatChem
Influence of carbon on molybdenum carbide catalysts for the hydrogen evolution reaction
ChemCatChem
A review of molybdenum catalysts for synthesis gas conversion to alcohols: catalysts, mechanisms and kinetics
Catal Rev
Molybdenum-carbide-modified nitrogen-doped carbon vesicle encapsulating nickel nanoparticles: a highly efficient, low-cost catalyst for hydrogen evolution reaction
J Am Chem Soc
Nanocrystalline Mo2C as a bifunctional water splitting electrocatalyst
ChemCatChem
Sulfur-decorated molybdenum carbide catalysts for enhanced hydrogen evolution
ACS Catalysis
Characterization of molybdenum carbides for methane reforming by TPR, XRD, and XPS
J Phys Chem B
Adsorption equilibria of CO coverage on β-Mo2C surfaces
J Phys Chem C
Cited by (34)
Pyrolysis of lignocellulosic, algal, plastic, and other biomass wastes for biofuel production and circular bioeconomy: A review of thermogravimetric analysis (TGA) approach
2022, Renewable and Sustainable Energy ReviewsHigh-efficiency recycling method for Mo and Ni from spent catalyst via soda roasting and solvent extraction
2022, Journal of Cleaner ProductionCitation Excerpt :First, the spent catalyst is heated to remove the deposited carbon and is subsequently roasted with Na2CO3. The soda roasting process accompanied by hot water leaching is a highly efficient Mo transformation technique compared to direct acidic leaching and blank roasting with acidic leaching (Alaba et al., 2018). Although soda roasting is an established method, more attention should be paid to the application of soda roasting to the transformation of Mo from insoluble into soluble forms.
Restructuring of the gold-carbide interface for low-temperature water-gas shift
2022, Chemical CommunicationsThe surface phase structure evolution of the fcc MoC (001) surface in a steam reforming atmosphere: systematic kinetic and thermodynamic investigations
2022, Catalysis Science and Technology