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The most widely used catalyst for the hydrogen evolution reaction (HER) is Pt, but the high cost and low abundance of Pt need to be urgently addressed. Single-atom catalysts (SACs) have been an effective means of improving the utilization of Pt atoms. In this work, we used a nonmetal (NM = B, N, O, F, Si, P, S, Cl, As, Se, Br, Te, and I) doped β-Mo 2 C (100) C-termination surface as the support, with Pt atoms dispersed on the support surface to construct Pt@NM-Mo 2 C. Using density functional theory (DFT) calculations, we selected catalysts with excellent HER activity. Among 117 candidate catalysts, 49 catalysts exhibited ideal catalytic performance with Gibbs free energy of hydrogen intermediate (H*) adsorption (Δ G H* ) values less than 0.2 eV. The Δ G H* values of 16 catalysts were even lower than that of Pt (Δ G H* ≈ 0.09 eV), with Pt I @N 2/4-a -Mo 2 C demonstrating the best performance (Δ G H* = -0.01 eV). Combined with electronic structure analysis, we could understand the impact of charge transfer between Pt and the underlying NM atoms on the strength of the Pt-H bond, thereby promoting HER activity. Using machine learning (ML), we identified that the primary influencing factors of the HER catalytic activity in the Pt@NM-Mo 2 C system were the Bader charge transfer of Pt ( N ePt ), the d-band center of Pt (ε dPt ), and the atomic radius of NM ( R NM ), with N ePt having the greatest impact on the HER catalytic activity.

• There exists a strong interaction between Pd and β-Mo 2 C. • Atomically dispersed Pd species with positive charge is formed. • The formation of Pd hydride is inhibited. • The excessive hydrogenation is avoided. • The adsorption of ethylene is weakened. Molybdenum carbide is a promising support to tune the metal reactivity, which originates from the interaction between metal and support. In this work, Pd/β-Mo 2 C was prepared using a deposition-precipitation method for selective hydrogenation of acetylene. The high temperature calcination is employed to modulate the interaction between Pd and β-Mo 2 C. The Pd/β-Mo 2 C catalyst calcined at 600 °C exhibits significant promotion in selective hydrogenation, which shows 100 % acetylene conversion and 81.4 % ethylene selectivity at 160 °C. The activity promotion originates from the enhanced electronic metal-support interaction, which induces a shift of Pd 3d to higher binding energy. Besides, the Pd species become atomically dispersed after calcination. The changes in geometric and electronic structure suppress the formation of Pd hydrides, which consequently inhibits the excessive hydrogenation capacity of Pd. The structure variation also affects the adsorption of ethylene. No strong adsorbed ethylene (di-σ bonded ethylene) can be identified, which is conducive to the improvement of ethylene selectivity. Density functional theoretical (DFT) calculations confirm that Pd on β-Mo 2 C is positively charged. The desorption energy of C 2 H 4 * (0.78 eV) is significantly lower than that of further hydrogenation (1.45 eV), which explains the improved ethylene selectivity of the calcinated catalyst. The present study indicates calcination is an effective method to tune the activity of Pd/β-Mo 2 C for reactions beyond selective hydrogenation of acetylene. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Exploring earth-abundant and noble metal-free catalysts for water electrolysis is pivotal in renewable hydrogen production. Herein, a highly active electrocatalyst of nitrogen-doped porous carbon nanosheets coupled with Mo2C nanoparticles (Mo2C/NPC) was synthesized by a novel method with high BET surface area of 1380 m2 g−1 using KOH to activate carbon composite materials. The KOH plays a key role in etching out MoS2 to produce Mo precursor; simultaneously, it corrodes carbon to form porous structure and produce reducing gas such as H2 and CO. The resulting Mo2C/NPC hybrid demonstrated superior HER activity in acid solution, with the overpotential of 166 mV at current density of 10 mA cm−2, onset overpotential of 93 mV, Tafel slope of 68 mV dec−1, and remarkable long-term cycling stability. The present strategy may provide a promising strategy to fabricate other metal carbide/carbon hybrids for energy conversion and storage.

• We reveal that the Mo 2 C(1 0 0) surface is covered by a monolayer of oxygen atoms under HER turnover condition. • The chemisorbed oxygen atoms on Mo 2 C(1 0 0) are identified as the active sites for HER. • The HER activity of Mo 2 C(1 0 0) shows a positive correlation with its oxidation degrees. Large-scale production of hydrogen fuels via electrochemical water splitting requires efficient and cost-effective electrocatalysts. Molybdenum carbide (Mo 2 C), as a promising substitute for expensive Pt-based catalysts, exhibits outstanding electrocatalytic performance toward hydrogen evolution reaction (HER). Herein, by combining theoretical studies and experimental measurements, we systematically investigate the surface stability and HER activity of Mo 2 C. We demonstrate that the Mo 2 C(1 0 0) surface is oxidized under HER turnover condition, and the HER activity shows a positive correlation with the oxidation degrees of this surface. The Mo 2 C(1 0 0) surface covered by a monolayer of oxygen atoms is verified as the most stable surface structure, which derives the optimum HER activity, and thus the surface chemisorbed oxygen atoms are identified as the active sites. This study provides new insights into developing efficient electrocatalysts for HER based on Mo 2 C. [ABSTRACT FROM AUTHOR]

Molybdenum carbide (β-Mo 2 C) possesses excellent electrical conductivity, good thermal and chemical stability, and is, therefore, a promising candidate material for electromagnetic (EM) shielding in diverse harsh environments. Herein, for the first time, β-Mo 2 C based ultra-thin films were prepared through in-situ growth of the carbide on a self-assembled graphene oxide (GO) film. The remaining reduced GO (RGO) layers located in between two adjacent Mo 2 C nanoparticles not only can work as flexible binder to impart the resultant films excellent flexibility but also enable the formation of heterogeneous nano-interface which is beneficial for the improvement of shielding by absorption. The amounts of β-Mo 2 C in the resultant films were adjusted through varying the Mo precursor contents. With the introduction of β-Mo 2 C phase in the resultant film, the shielding effectiveness (SE) increased significantly. At the thickness of ∼25 μm, the highest SE reaches 46.8 dB compared to 21.6 dB of the pristine RGO film. With the increase of the Mo 2 C content in the resultant materials, the density increased from 0.32 to 1.23 g/cm3. The resultant Mo 2 C film exhibit an SSE/t (specific SE by thickness) value of as high as 15,971 dB cm2 g−1. Image 1 [ABSTRACT FROM AUTHOR]

The advancement of innovative Mo 2 C anode yet faces the challenge of exploring a simple, convenient and controllable synthetic route. β-Mo 2 C was prepared by utilizing low-cost hexamethylenetetramine and ammonium molybdate as raw materials and employing simple calcination treatment under N 2 atmosphere. When applied as an anode for lithium ion batteries (LIBs), β-Mo 2 C delivers a satisfactory rate performance (147.0 and 103.4 mAh g−1 at 0.5 and 1.0 A g−1) and excellent cyclic stability (72.2 mAh g−1 at 2.0 A g−1 after 1500 cycles). Meanwhile, a suitable voltage plateau at ∼1.4 V for β-Mo 2 C also avoids the formation of lithium dendrites to improve the safety of LIBs. β-Mo 2 C with high electronic conductivity and suitable lithium storage potential was prepared by utilizing low-cost hexamethylenetetramine and ammonium molybdate as raw materials and employing simple calcination treatment under N 2 atmosphere. [Display omitted] • β-Mo 2 C was prepared by simple calcination treatment under N 2 atmosphere. • A suitable voltage plateau (∼1.4 V) for β-Mo 2 C avoids the formation of Li dendrite. • β-Mo 2 C delivered a satisfactory rate performance and excellent cyclic stability. [ABSTRACT FROM AUTHOR]

The CO 2 -assisted oxidative dehydrogenation reaction can possibly become a more sustainable alternative for the production of light olefins. Due to the endothermic nature of this reaction, elevated reaction temperatures are required to achieve conversion levels of interest, with competing side reactions as result. In this study, the effect of reaction temperature on the performance of silica supported molybdenum carbide nanoparticles is investigated. At all applied reaction temperatures, the maximum possible ethylene selectivity of 67 C-% is achieved. An increase in reaction temperature decreases the oxidation of the catalyst under reaction conditions. However, a clear phase change effect on the various carbide allotropes suggests that an oxidation/re-carburization mechanism occurs from β-Mo 2 C to MoO x C y /MoO 2 to α-MoC 1−x /β-Mo 2 C, rather than a prevention of the oxidation in the first place. Nevertheless, catalyst deactivation was still observed and can be assigned to carbon formation on the surface of the catalyst, blocking active sites. [Display omitted] • Mo 2 C on SiO 2 performs CO 2 -ODH with minimal occurrence of side reactions. • Severe oxidation of β-Mo 2 C to MoO 2 during low temperature CO 2 -ODH. • High temperature CO 2 -ODH re-carburizes MoO 2 to MoO x C y followed by α-MoC 1−x. • Extensive characterization of spent catalyst using XRD, XANES and Raman. [ABSTRACT FROM AUTHOR]

Toluene, n-heptane, and methane were studied as carbon sources during the synthesis of Mo2C. Ammonium heptamolybdate ((NH4)6Mo7O24·4H2O), molybdenum dioxide (MoO2), orthorhombic molybdenum trioxide (α-MoO3), and a low crystallinity molybdenum oxide (MoO x) were employed as metal precursors and their conversion into the carbide phase was followed by time-resolved X-ray diffraction from synchrotron radiation. Thermal treatment was carried out from 298 K up to 1023 K and the evolution of gases analyzed by mass spectrometry. The resulting carbidic phase obtained using methane/H2 was hexagonal β-Mo2C, while in contrast, cubic molybdenum carbide (α-MoC1- x) was obtained when toluene/H2 or n-heptane/H2 were employed, which occurred independently of the original metal precursor. Molybdenum carbide was first detected, on average, at about 923 K. Mass spectrometry results show the formation of CO when methane was used as a carbon source, while methyl radicals and benzene and mainly methyl radicals were detected when toluene and n-heptane were employed, respectively. [ABSTRACT FROM AUTHOR]

Non-thermal plasma (NTP) coupled with catalysis provides a way to enable the dry reforming of methane (DRM) reaction to occur at low temperatures. While assistance of NTP brings the negative issue of coke deposition due to the faster rate of CH 4 dissociation induced by NTP. Herein, β-Mo 2 C was employed as an effective component to activate CO 2 and collaborated with Ni/γ-Al 2 O 3 for the plasma-assisted DRM reaction. Addition of β-Mo 2 C facilitated the charge deposition, and Ni nanoparticles were found to re-disperse over the β-Mo 2 C surface due to the strong interaction between Ni and β-Mo 2 C. Benefiting from the new active interface of Ni-Mo 2 C, the mechanically mixed Mo 2 C-Ni/Al 2 O 3 catalyst exhibited much better activity and stability as compared with the undoped Ni/Al 2 O 3 catalyst. The present study reveals the crucial roles of β-Mo 2 C additives, providing practical solutions to depress carbon deposition, and thereby enhance the catalytic stability in plasma-assisted DRM reaction. [Display omitted] • β-Mo 2 C collaborated with Ni/γ-Al 2 O 3 for the coupled plasma-catalysis DRM reaction. • β-Mo 2 C facilitated the charge deposition and higher energy efficiency being obtained. • Redispersion of Ni NPs over β-Mo 2 C forming Ni-Mo 2 C interface. • A matching conversion rate of CH 4 with that of CO 2 being obtained. [ABSTRACT FROM AUTHOR]

Abstract: Potassium-promoted β-Mo2C catalysts were prepared and their performances in CO hydrogenation were investigated. The main products over β-Mo2C catalyst were C1–C4 hydrocarbons, only ∼4 C-atom% alcohols were obtained. The products of hydrocarbons and alcohols obeyed traditional linear Anderson–Schultz–Flory (A–S–F) distribution. However, modification with K2CO3 resulted in a remarkable selectivity shift from hydrocarbons to alcohols. Moreover, it was found that potassium promoter enhanced the ability of chain propagation of β-Mo2C catalysts and resulted in a higher selectivity to C2+OH. For K/β-Mo2C catalysts, the hydrocarbon products also obeyed traditional linear A–S–F plots, whereas alcohols gave a unique linear A–S–F distribution with remarkable deviation of methanol compared with that on β-Mo2C catalyst. It could be concluded that potassium promoter might exert a prominent function on the whole chain propagation to produce alcohols. A surface phase on the K/β-Mo2C catalysts such as the “K–Mo–C” explained the higher value for C2+OH, especially could promote the step of C1OH to C2OH, or could have a role in producing directly C2OH, but again this would be speculative. At the same time, the influence of the loadings of K2CO3 on the performances of β-Mo2C catalyst was investigated and the results revealed that the maximum yield of alcohol was obtained at K/Mo molar ratio of 0.2. [Copyright &y& Elsevier]

Abstract: Potassium and nickel doped β-Mo2C catalysts were prepared and their performances of CO hydrogenation were investigated. The main products over β-Mo2C catalyst were hydrocarbons, and only few alcohols were obtained. The potassium promoter resulted in remarkable selectivity shift from hydrocarbons to alcohols over β-Mo2C. Moreover, it was found that the potassium promoter enhanced the ability of chain propagation of β-Mo2C catalyst and resulted in a higher selectivity to C2+OH. When doped by potassium and nickel, β-Mo2C catalyst showed high activity and selectivity for mixed alcohols synthesis, the Ni promoter further enhanced the whole chain propagation to produce alcohols especially for the step of C1OH–C2OH. From the XPS analysis, it had been proved that the formation of higher alcohols might be attributable to the presence of MoIV species, whereas the formation of hydrocarbons was closely associated with the presence of MoII species on the surface of the catalysts. [Copyright &y& Elsevier]

• Molybdenum carbides of different crystal phases have been prepared and experimentally compared. • Molybdenum carbide exhibited excellent aromatics selectivity in quinoline hydrodenitrogenation, and this catalytic process was characterized by low hydrogen consumption. • The excellent performance of the catalyst was explained from the perspective of characterization and density functional theory. • The hypothesis of multiple active sites on molybdenum carbide was proposed. The hydrodenitrogenation (HDN) with a low hydrogen consumption in the hydroprocessing of crude oils derived from carbon resources is still a challenge. Here, a molybdenum carbide (α-MoC 1-x) catalyst with a high selectivity to aromatic compounds was reported, using the HDN of quinoline as a model reaction. This process was characterized by low hydrogen consumption. The prepared α-MoC 1-x had a much larger specific surface area (107.6 m2•g−1) than β-Mo 2 C (6.8 m2•g−1). Under the catalysis of α-MoC 1-x , the conversion and the denitrification rate of quinoline could both reach 99%, and the highest selectivity of the total aromatics reached 48.5% at 360 °C, which was 10.7% higher than that on β-Mo 2 C. The cleavage of C C bonds of side chain of Propylbenzene (PB) and Propylcyclohexane (PCH) occurred, producing several unexpected products with unusual high selectivity. A new possible reaction network of quinoline hydrodenitrogenation was drawn, and the reaction mechanism was discussed based on the experiments and DFT (density functional theory) calculations. [Display omitted] [ABSTRACT FROM AUTHOR]

Lamellar β-Mo 2 C and α-MoC 1-x are synthesized by a self-assemble synthetic route using Mo-dopamine as single source at low carburization temperature. Due to more active sites and higher site density, β-Mo 2 C presents superior HDO performance than that of α-MoC 1-x. [Display omitted] • Lamellar β-Mo 2 C and α-MoC 1-x are prepared by one-step pyrolysis of Mo-dopamine. • β-Mo 2 C performs better performance in HDO of diphenyl ether than that of α-MoC 1-x. • Structure difference leads to discrepant performance of β-Mo 2 C and α-MoC 1-x. • β-Mo 2 C catalyst presents good stability during the time on stream test. The controllable synthesis of molybdenum carbides with different phases by a facile and environmentally friendly method and understanding their structure-performance relationship are still challenges. In this work, lamellar β-Mo 2 C and α-MoC 1-x have been synthesized by a self-assembly synthetic route using Mo-dopamine as single source without any template and additive at a relatively low carburization temperature. The introduction of H 2 fortifies the reducibility of the system and accelerates the carburization process and phase transformation. The structure-performance relationship was also investigated in the hydrodeoxygenation (HDO) of diphenyl ether. Thereinto, β-Mo 2 C exhibits 99.9% conversion and 95.2% selectivity to benzene, while α-MoC 1-x shows only 74.6% conversion with 84.8% selectivity to benzene and 12.7% to O-containing product phenol at the same conditions. The superior HDO performance of β-Mo 2 C can be attributed to the more active sites in β-Mo 2 C than α-MoC 1-x. β-Mo 2 C with stronger thermostability exhibits long-term stability during the HDO process. The results show that β-Mo 2 C is a promising catalyst for lignin valorization. [ABSTRACT FROM AUTHOR]

Exploring earth-abundant and noble metal-free catalysts for water electrolysis is pivotal in renewable hydrogen production. Herein, a highly active electrocatalyst of nitrogen-doped porous carbon nanosheets coupled with Mo2C nanoparticles (Mo2C/NPC) was synthesized by a novel method with high BET surface area of 1380 m2 g−1 using KOH to activate carbon composite materials. The KOH plays a key role in etching out MoS2 to produce Mo precursor; simultaneously, it corrodes carbon to form porous structure and produce reducing gas such as H2 and CO. The resulting Mo2C/NPC hybrid demonstrated superior HER activity in acid solution, with the overpotential of 166 mV at current density of 10 mA cm−2, onset overpotential of 93 mV, Tafel slope of 68 mV dec−1, and remarkable long-term cycling stability. The present strategy may provide a promising strategy to fabricate other metal carbide/carbon hybrids for energy conversion and storage. [ABSTRACT FROM AUTHOR]