Hollow Hemispherical Carbon Microspheres with Mo₂C Nanoparticles Synthesized by Precursor Design: Effective Noble Metal‐Free Catalysts for Dehydrogenation

Abstract

photocatalytic hydrogen evolution reactions, techno-economically feasible ways to store and transport it need to be developed. [2,3] Liquid organic hydrides (LOHs, e.g., cyclohexane) are considered among the most viable H 2 carriers for safe transport and use of H 2. [4] However, to deploy LOHs as H 2 storage and release media for practical applications, facile catalytic methods that enable the dehydrogenation of LOHs are needed. Thus, there is ongoing research to develop efficient and cost-effective catalysts for the dehydrogenation of LOHs. [5,6] Owing to their high catalytic activity, noble metals such as Pt have traditionally been used for the dehydrogenation of LOHs. [7] Recently, more research is being carried out to reduce the overall amount of noble metals used in such catalysts without compromising the overall activities of the catalysts, e.g., by alloying the noble metals with other inexpensive elements. [8] However, these types of catalysts are still difficult to fully scale up due to the high cost and scarcity of the noble metals included in them. Therefore, additional research should be done to develop alternative, sustainable, and scalable catalysts for the dehydrogenation of LOHs and other related reactions. [9] Transition metal carbides (TMCs) have long been known to have Pt-like d-band electronic structures, optimal hydrogen adsorption properties, and similar catalytic properties as Pt. [10,11] Thus, they have been the subject of many recent Noble metal-based catalysts are currently widely used for the dehydrogenation of hydrocarbons or the production of H 2 from hydrocarbons for various applications. However, these catalysts are expensive and hard to scale up. In this work, a facile template-assisted synthesis of hollow carbon microspheres possessing ultrasmall molybdenum carbide (Mo 2 C) nanoparticles (NPs) that can efficiently catalyze the dehydrogenation of hydrocarbons is reported. The hollow structures and catalytic activity of the materials can be tuned, or optimized, by controlling the relative amount of Mo species or template used in their precursors. The bowl-like hemispherical carbons with ≈20 nm thin shells and <5 nm in diameter Mo 2 C NPs show superior catalytic activity for dehydrogenation of cyclohexane, with a turnover frequency value of 1 × 10 −4 s −1 at 305 °C. The catalytic activity of these microspheres for the reaction is 15 times higher than that of the corresponding incomplete hollow spherical carbon microparticles possessing similar sized Mo 2 C NPs and also better than that of activated carbon-supported Pt (Pt/AC). Interestingly also, adding a mere 0.1% Pt into the materials leads to several-fold increase in their catalytic activity and much higher activity than that of Pt/AC.

Mesoporous Carbon Nanotablets Coupled with Mo2C Nanoparticles: Combining Morphology and Structure to Realize High Activity for Efficient Hydrogen Evolution

“…65‐8766). The structure information was further obtained by Raman and N 2 ad‐/desorption analysis.As shown in Figure g, the peaks centred at 818 and 992 cm −1 for nanotablets material confirm the formation of Mo 2 C, and the broad shoulder peaks located at ca. 1350 cm −1 and 1590 cm −1 are magnified and displayed in inset of Figure g, which are matched to the D and G bands originated from the defective carbon and graphitic carbon, respectively .…”

“…Due to their similarity to the d‐band electronic structure, perfect electrical conductivity and excellent hydrogen‐adsorption propertiesof Pt, transition metal carbides such as molybdenum carbide (Mo 2 C) have been accepted as the promising and alternative Pt‐free catalysts for the involving‐hydrogen reaction . Particularly, Mo 2 C hybrids behave as high active in the water splitting‐involved reaction .…”

“…Due to their similarity to the d-band electronic structure, perfect electrical conductivity and excellent hydrogen-adsorption propertiesof Pt, transition metal carbides such as molybdenum carbide (Mo 2 C) have been accepted as the promising and alternative Pt-free catalysts for the involving-hydrogen reaction. [12][13][14][15] Particularly, Mo 2 C hybrids behave as high active in the water splitting-involved reaction. [16][17][18] Recently, the reported works mainly focus on constructing of molybdenum carbide and nanocarbon hybrids to confine the growth of Mo 2 C nanoparticles (NPs), containing octahedrons nanocarbon, [17] nanowires, [19] carbon nanofibers, [20] carbon nanotubes, [21] nanosheets, [22] hollow nanosphere [23] and meshlike carbon nanlayers.…”

Controllable N Doped in Carbon Nanolayers@Mo2C Nanodots as Electrocatalyst Boosts High‐Efficient Hydrogen Production

“…The peak at 819 cm −1 can be attributed to formation of molybdenum carbide. [ 12 ] The D‐band peak at 1357 cm −1 and the G‐band peak at 1589 cm −1 is observed, and the peak intensity ratio ( I D / I G ) of Mo 2 C/NC, Mo 2 C/NC‐1, Mo 2 C/NC‐2, Mo 2 C/NC‐3 are 0.92, 0.96, 0.97, and 0.99, respectively. Obviously, the I D / I G values increase as the amount of melamine is increased, indicating that structural defects can be controlled by adding melamine.…”

Synthesis of One‐Dimensional Mo2C‐Embedded Carbon Nanofibers with Enhanced Lithium Storage Capacity for Lithium‐Ion Batteries

“…The value of I D /I G = 1.24, calculated from the Raman spectroscopy, further affirms the presence of a higher concentration of disordered CÀ C bond. [41][42][43] The observation of the presence of more disordered carbon than graphitic carbon even at the calcination temperature of 1000 °C could be due to the larger content of embedded Mo 2 C within the carbon fibers. The other peaks appearing at 720, 832, and 1005 cm À 1 correspond to the Mo 2 C phase, which is in agreement with the XRD results of the hexagonal phase of Mo 2 C as reported earlier.…”