Comparison of the Surface State of Ni Nanoparticles Used for Methane Catalytic Decomposition

Abstract

Nickel nanoparticles were synthesized by two different routes and their reactivity was assessed during methane catalytic decomposition (MCD) conducted in situ in a thermogravimetric analyzer at atmospheric pressure from room temperature to 930°C. Commercially available nickel nanoparticles were also evaluated for comparative purposes. Carbon buildup was monitored continuously to provide a qualitative comparison of the rate of the reaction for all the systems, while residues composed of nickel nanoparticles and carbon nanotubes (CNTs) were collected at different stages for further evaluation by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The surface composition of the fresh nickel nanoparticles was clearly sensitive to the preparation method and was presumably responsible for the trends observed during the catalytic evaluation. On one hand, an early onset in the temperature of the catalytic reaction at 400°C is distinguished by Ni nanoparticles prepared in a one-step direct thermal decomposition of nickel acetate tetrahydrate while, under the same conditions, Ni nanoparticles produced by an alternative emulsion-mediated synthesis reacted at T > 480°C. When MCD is finished at 930°C, multiwalled carbon nanotubes (MWCNTs) and bamboo-shaped carbon nanotubes (BSCNTs) structures are collected selectively in the systems catalyzed by particles prepared by one-step and emulsion-mediated synthesis, respectively. Commercial nickel nanoparticles, on the other hand, produced low quality CNTs in a comparatively much slower fashion. Methane catalytic decomposition conducted in a thermogravimetric analyzer provides a complementary tool to compare in situ reactivity of nanoparticles and to isolate them for further ex situ characterization.

Ni/H-ZSM-5 as a stable and promising catalyst for COx free H2 production by CH4 decomposition

“…8 Nickel is a common transition metal used for the conversion of methane. [9][10][11][12][13][14][15][16] The most important factors that inuence the carbon deposits during methane decomposition are the particle size, dispersion and stabilization of the metallic nickel particle by selecting appropriate support. Michalkiewicz and co-workers critically reviewed the effect of reaction temperature on the carbon growth due to the Ni loading and also the nature of support that would strongly inuence the H 2 yields as well as the quality of the CNTs formed during the CDM process.…”

Size dependence of the magnetic properties of Ni nanoparticles prepared by thermal decomposition method

“…For the fabrication of Ni nanoparticles, methods such as sputtering [ 13 , 14 ], solution glow discharge [ 15 ], pulsed laser ablation [ 6 ], reversed micelles [ 16 ], thermal decomposition [ 17 - 20 ], and wet chemical reduction [ 7 , 21 , 22 ] are used. Among them, the ones based on thermal decomposition are preferred.…”

The Key Points of Highly Stable Catalysts for Methane Reforming with Carbon Dioxide

“…Among them, Ni‐based catalysts are preferred for their high activity and low price, which, however, deactivate rapidly due to carbon deposition and Ni particle sintering 9–12. Heavy carbon nanotube (CNT) growth can be observed under reaction conditions,13–16 resulting in the structure destruction of the catalysts (Supporting Information, Scheme S1), which is the first problem to the catalyst stability. The coke on catalyst support and the sintering of the active Ni components are the other two major problems devastating to the catalyst stability.…”