Promoting Role of Amorphous Carbon and Carbon Nanotubes Growth Modes of Methane Decomposition in One-Pot Catalytic Approach

Lifang Chen,Ulises Arellano,Luis Enrique Noreña,Oscar Arturo González Vargas,Roberto Limas,Jin An Wang

doi:10.3390/catal11101217

Abstract

We report the simultaneous production of hydrogen fuel and carbon nanotubes (CNTs) via methane dehydrogenation catalyzed with Ni/SBA-15. Most Ni nanoparticles (NPs) with size between 10 and 30 nm were highly dispersed on SBA-15 and most of them had a strong interaction with the support. At temperatures ranging from 500 to 800 °C, methane could be decomposed to release hydrogen with 100% selectivity at conversion between 51 and 65%. There was no CO or CO2 detectable in the reaction fluent. In the initial stage of the reaction, amorphous carbon and dehydrogenated methane species adsorbed on the Ni NPs promoted the CH4 decomposition. The amorphous carbon atoms were then transformed into carbon nanotubes which chiefly consisted of a multiwall structure and grew towards different orientations via a tip-growth or a base-growth modes, controlled by the interaction strength between the Ni NPs and the SBA-15 support. Reaction temperature affected not only methane conversion, but also the diffusion of carbon atoms on/in the Ni NPs and their precipitation at the interfaces. At higher temperature, bamboo-like CNTs or onion-like metal-encapsulated carbons were formed, mainly due to the rate of carbon atom formation greater than that of carbon precipitation for CNTs construction. The CNTs formation mechanisms are discussed and their growth modes under different conditions are proposed.

Highlights

Natural gas is a versatile and efficient fuel resource with a wide spectrum of applications, principally in the electronic power plants, residential and transportation uses
Afterwards, water in the mixture was removed at 110 ◦C; the resultant sample was dried at 110 ◦C for 12 h and calcined at 800 ◦C for 4 h in air for Catalysts 2021, 11, 1217 slowly formed and a hydroxide solid layer was formed on the outer surface of the SBA-15 during 24 h of reaction
In the CH4 catalytic decomposition reaction, the amorphous carbon predominately formed at the beginning of the methane decomposition reaction over Ni/SBA-15 catalysts, which may promote CH4 dehydrogenation

Summary

Introduction

Natural gas is a versatile and efficient fuel resource with a wide spectrum of applications, principally in the electronic power plants, residential and transportation uses. One of the alternatives is to use it for the simultaneous production of COx–free hydrogen-rich fuel and nanocarbon materials through a one-pot catalytic approach, i.e., the catalytic decomposition technique [1,2,3,4,5]. It is a fully green chemistry process due to zero pollutants release. As the products of this catalytic process are gaseous hydrogen and solid carbon, they can be automatically separated. This reaction does not produce CO and CO2; there is no need of subsequent processes for COx separation

Methods

Results

Conclusion