Molybdenum Carbide Modified Nanocarbon Catalysts for Alkane Dehydrogenation Reactions

Abstract

Nucleophilic sites on nanocarbon catalysts act as promoters for homolytic cleavage of aliphatic C–H bond. In this study, we report a hybrid catalyst composed of Mo2C and nitrogen-doped onion-like carbon (NOLC) with enhanced capability for C–H bond activation in direct dehydrogenation (DH) reaction of ethylbenzene (EB). The enhanced activity of the Mo2C/NOLC catalyst over unmodified NOLC in EB DH is attributable to the promoted C–H bond activation by Mo2C, as characterized by the lower activation energy and the kinetic isotope effect using deuterated EB. Our XPS, XRD, and Raman spectroscopy results show that the hybrid catalyst is structurally robust under the reaction condition. The increase in nucleophilicity of the oxygen active sites in NOLC is evidenced by an overall shift of the O 1s peaks to lower binding energies after Mo2C modification. The DFT calculation further provides mechanistic insights into the electron-transfer process from Mo2C to the ketonic carbonyl groups.

Fabrication of Polydopamine Modified Carbon Nanotube Hybrids and their Catalytic Activity in Ethylbenzene Dehydrogenation

“…As shown in Figure b, the binding energy of all these four types of oxygen species shifted to lower value (∼0.4 eV lower) in O1s XPS of OCNT‐PD‐600, indicating the improved nucleophilicity of oxygen functionalities on nanocarbon matrix after PD modification. This phenomenon is consistent with previous observations that the electron transfer could happen between metal (carbides or oxides) and nanocarbon in the complex system . The electron rich PD species may donate electrons to nanocarbon matrix, and the improved nucleophilicity of the oxygen functionalities (especially ketonic carbonyl groups serving as active sites) promoted the C−H bond activation ability and the intrinsic activity of nanocarbon catalysts.…”

“…Base on Arrhenius Equation, the reaction rate measured at different temperature yields the apparent activation energy (Ea) of the dehydrogenation reactions on OCNT‐PD‐X catalysts. As it is acknowledged that the activation of C−H bond is the rate determining step for ethylbenzene dehydrogenation reactions, the value of Ea could directly reflect the ability of the catalyst to activate (break) C−H bond . As shown in Figure a, the apparent activation energy of EB DH on OCNT‐PD‐800 is 77 kJ mol −1 , which is much lower than that on pristine OCNT (94 kJ mol −1 ), indicating that the activation of C−H bond is promoted after PD modifications.…”

“…It is revealed experimentally and theoretically that the activation of aliphatic C−H bond on ethyl group is the rate determining step in this reaction, and the C−H bond activation ability of nanocarbon can be promoted via adjusting the red‐ox property by modifying the chemical composition and electronic structure of nanocarbon materials. For instance, we have recently reported that covalent incorporation of molybdenum carbide clusters could lead to the electron transfer to carbon matrix thus increasing the nucleophilicity of nanocarbon materials and their DH catalytic activity . However, the long term stability of the Mo 2 C/carbon hybrid catalysts is not good enough because of the volatilization of the molybdenum species.…”

Three‐Dimensional Interconnected Porous Nitrogen‐Doped Carbon Hybrid Foam for Notably Promoted Direct Dehydrogenation of Ethylbenzene to Styrene

“…[32] In recent years, metal-free nanocarbon catalysts have shown remarkable performance in various reactions, such as photocatalytic hydrogen evolution, direct dehydrogenation of alkanes and Friedel-Crafts reactions. [39][40][41][42] However, the catalytic system is typically carried out at high temperature (600-650°C) with excess stream provided simultaneously to alleviate carbon deposit during the dehydrogenation. [39][40][41][42] However, the catalytic system is typically carried out at high temperature (600-650°C) with excess stream provided simultaneously to alleviate carbon deposit during the dehydrogenation.…”

“…[33][34][35][36][37][38] Styrene, an important chemical monomer for the synthesis of polymers like polystyrene, is primarily produced from direct dehydrogenation of ethylbenzene over commercial potassium-promoted iron oxide at the present. [39][40][41][42] However, the catalytic system is typically carried out at high temperature (600-650°C) with excess stream provided simultaneously to alleviate carbon deposit during the dehydrogenation. Although high styrene selectivity and yield are achieved, massive energy and water consumption are still harmful to the environment, thus a clean and economic ethylbenzene dehydrogenation process and efficient catalyst are of great demand for the production of styrene.…”