Hybrid Nanocarbon as a Catalyst for Direct Dehydrogenation of Propane: Formation of an Active and Selective Core–Shell sp²/sp³Nanocomposite Structure

Abstract

Hybrid nanocarbon, comprised of a diamond core and a graphitic shell with a variable sp(2)-/sp(3)-carbon ratio, is controllably obtained through sequential annealing treatment (550-1300 °C) of nanodiamond. The formation of sp(2) carbon increases with annealing temperature and the nanodiamond surface is reconstructed from amorphous into a well-ordered, onion-like carbon structure via an intermediate composite structure--a diamond core covered by a defective, curved graphene outer shell. Direct dehydrogenation of propane shows that the sp(2)-/sp(3)-nanocomposite exhibits superior catalytic performance to that of individual nanodiamond and graphitic nanocarbon. The optimum catalytic activity of the diamond/graphene composite depends on the maximum structural defectiveness and high chemical reactivity of the ketone groups. Ketone-type functional groups anchored on the defects/vacancies are active for propene formation; nevertheless, once the oxygen functional groups are desorbed, the defects/vacancies alone might be active sites responsible for the C-H bond activation of propane.

Oxidative Dehydrogenation on Nanocarbon: Intrinsic Catalytic Activity and Structure–Function Relationships

“…It should be noted that this value indicates the surface concentration of active sites that are "working" under the given reaction conditions and it is not necessarily the same as the surface concentration of the ketonic carbonyl groups on fresh catalysts.F irst, some of the carbonyl functionalities are not accessible as ar esult of the porous structure of nanocarbons.S econd, complex transformations occur between surface defects and various oxygen functionalities (such as hydroxys,carboxylic acids,and ethers) under ODH conditions. [10] This is also the reason for the residual reactivity of the catalysts after titration as shown in Figure 1. Thec hemically active defects easily chemisorb oxygen and are oxidized under the reaction conditions.…”

“…[8,9] However, identifying and quantifying these functionalities using current spectroscopy-based techniques,s uch as X-ray photoelectron spectroscopy (XPS) or temperature-programed desorption (TPD), presents as ignificant challenge because of the similarities in molecular weight and physical/chemical properties between the different oxygen moieties. [10][11][12] The chemical titration (passivation) method could provide the surface concentration of major oxygen functionalities on carbon nanotube (CNT) surfaces. [13,14] However,t he ex situ process cannot provide any information on the active sites under steady-state conditions and it also requires as eries of samples and tedious steps,w hich is not practical for kinetic studies.T oconnect the chemical structure and quantity of the active sites to their steady-state intrinsic activity,wepropose here an in situ titration technique as shown in Scheme 1.…”

Nitrogen-doped carbon nanotubes via a facile two-step approach as an efficient catalyst for the direct dehydrogenation of ethylbenzene

“…[22][23][24][25][26][27][28][29][30][31][32] Post treatment includes thermal treatment, plasma treatment, and N 2 H 4 treatment. [42][43][44][45][46] Moreover, the introduction of nitrogen can improve the basic properties of carbon materials resulting in the promotion of dehydrogenation activity but inhibition of cracking side reaction of ethylbenzene by decreasing the amount of phenolic hydroxyl group, as well as can improve the nucleophilicity of ketonic CQO groups, and therefore can improve the activity of CQO for C-H activation. The incorporation of nitrogen atoms into the carbon matrix entirely takes place on the surface of the carbon nanostructures by post thermal treatment, where the reactions take place.…”

A Review of Carbon-Composited Materials as Air-Electrode Bifunctional Electrocatalysts for Metal–Air Batteries

“…In their structural characterizations, a comparison of HRTEM images and selected area electron diffraction (SAED) patterns of their B-OLC and OLC samples revealed the existence of multilayered sp 2 fullerene shells forming a quasi-spherical onion-like nanoparticle with particle sizes of 5-8 nm. The appearance of the graphite ring (002) in the SAED patterns also confirmed the effective conversion of nanodiamonds into sp 2 carbon phases with an identified interlayer spacing (~ 0.34 nm) that did not change after B-doping [59,60]. Based on the B 1s spectrum in XPS, six deconvoluted peaks were obtained at 185.…”