Oxidative Dehydrogenation on Nanocarbon: Insights into the Reaction Mechanism and Kinetics via in Situ Experimental Methods

Abstract

Sustainable and environmentally benign catalytic processes are vital for the future to supply the world population with clean energy and industrial products. The replacement of conventional metal or metal oxide catalysts with earth abundant and renewable nonmetallic materials has attracted considerable research interests in the field of catalysis and material science. The stable and efficient catalytic performance of nanocarbon materials was discovered at the end of last century, and these materials are considered as potential alternatives for conventional metal-based catalysts. With its rapid development in the past 20 years, the research field of carbon catalysis has been experiencing a smooth transition from the discovery of novel nanocarbon materials or related new reaction systems to the atomistic-level mechanistic understanding on the catalytic process and the subsequent rational design of the practical catalytic reaction systems. In this Account, we summarize the recent progress in the kinetic and mechanistic studies on nanocarbon catalyzed alkane oxidative dehydrogenation (ODH) reactions. The paper attempts to extract general concepts and basic regularities for carbon catalytic process directing us on the way for rational design of novel efficient metal-free catalysts. The nature of the active sites for ODH reactions has been revealed through microcalorimetric analysis, ambient pressure X-ray photoelectron spectroscopy (XPS) measurement, and in situ chemical titration strategies. The detailed kinetic analysis and in situ catalyst structure characterization suggests that carbon catalyzed ODH reactions involve the redox cycles of the ketonic carbonyl-hydroxyl pairs, and the key physicochemical parameters (activation energy, reaction order, and rate/equilibrium constants, etc.) of the carbon catalytic systems are proposed and compared with conventional transition metal oxide catalysts. The proposal of the intrinsic catalytic activity (TOF) provides the possibility for the fair comparisons of different nanocarbon catalysts and the consequent structure-function relation regularity. Surface modification and heteroatom doping are proved as the most effective strategies to adjust the catalytic property (activity and product selectivity etc.) of the nanocarbon catalysts. Nanocarbon is actually a proper candidate platform helping us to understand the classical catalytic reaction mechanism better, since there is no lattice oxygen and all the catalytic process happens on nanocarbon surface. This Account also exhibits the importance of the in situ structural characterizations for heterogeneous nanocarbon catalysis. The research strategy and methods proposed for carbon catalysts may also shed light on other complicated catalytic systems or fields concerning the applications of nonmetallic materials, such as energy storage and environment protection etc.

Oxidative Dehydrogenation on Nanocarbon: Revealing the Reaction Mechanism via In Situ Experimental Strategies

“…The direct catalytic applications of earth abundant carbon (especially nanocarbon) materials (carbon acting as active phase) have attracted considerable research interests in chemistry and material science during the past 20 years . The relatively high and stable catalytic activity of non‐metallic nanocarbon materials in alkane dehydrogenation,, organic compound selective oxidation ,[6,7] hydrogenation, and hydrohalogenation, reactions etc.…”

“…The direct catalytic applications of earth abundant carbon (especially nanocarbon) materials (carbon acting as active phase) have attracted considerable research interests in chemistry and material science during the past 20 years. [1][2][3] The relatively high and stable catalytic activity of non-metallic nanocarbon materials in alkane dehydrogenation, [4,5] organic compound selective oxidation , [6,7] hydrogenation, [8] and hydrohalogenation [9,10] reactions etc. sheds light on the possibility for the replacement and upgrade of conventional metal-based catalytic systems to meet the urgent demands of green and sustainable chemical engineering process in modern society.…”

Sulfate Surfactant Assisted Approach to Fabricate Sulphur‐Doped Supported Nanodiamond Catalyst on Carbon Nanotube with Unprecedented Catalysis for Ethylbenzene Dehydrogenation

“…To solve this problem, the sustainable nanocarbon materials, such as carbon nanotubes (CNT), nanodiamond (ND), carbon nanofibers (CNFs) and so on, become more and more popular among many fields including the dehydrogenation of ethylbenzene. These materials featured specific electric conductivity and catalytic properties . For example, CNT is a common nanocarbon material and features a hollow, tube‐like structure, sp 2 carbon atoms, perfect electro‐conductibility with large specific surface area, which results in its wide application in electrocatalysis and synthesis of new carbon materials for dozens of reactions with better application performance than traditional materials .…”

“…These materials featured specific electric conductivity and catalytic properties. [2,[17][18][19][20][21] For example, CNT is a common nanocarbon material and features a hollow, tube-like structure, sp 2 carbon atoms, perfect electroconductibility with large specific surface area, which results in its wide application in electrocatalysis and synthesis of new carbon materials for dozens of reactions with better application performance than traditional materials. [22][23][24][25][26][27][28][29][30][31] In addition to CNT, ND, prepared by detonation and featured sp2-sp3 core-shell structure, is also an attractive material widely used in synthesis of dye, electrocatalysis, heat catalysis, photocatalysis, semiconductor and biology.…”

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. [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.…”