CNT and H2 Production During CH4 Decomposition over Ni/CeZrO2. I. A Mechanistic Study

Agata Łamacz

doi:10.3390/chemengineering3010026

Abstract

This work presents a new insight into the potential of a Ni/CeZrO2 catalyst in two separate processes: (i) Chemical Vapor Deposition (CVD) using methane as a feedstock to obtain carbon nanotubes (CNTs) and H2, and (ii) catalyst regeneration with H2O that yields H2. The direct reaction of methane with H2O (steam methane reforming (SMR)) leads to H2 and CO (and CO2), whereas carbon deposition—regardless of its type—is an unwanted reaction. The concept presented in this work assumes dividing that process into two reactors, which allows one to obtain two valuable products, i.e., CNTs and H2. The literature data on CNT production via CVD ignores the issue of H2 formation. Moreover, there is no data concerning CNT production in fluidized bed reactors over ceria-zirconia supported metal catalysts. The results presented in this work show that CNTs can be formed on Ni/CeZrO2 during CH4 decomposition, and that the catalyst can be easily regenerated with H2O, which is accompanied by a high production of H2. The ability of Ni/CeZrO2 to be regenerated is its main advantage over the Ni-MgO catalyst that is popular for CNT production. This paper also shows that the Ni/CeZrO2 catalyst has the potential to be used for CNT and H2 production in a larger scale process, e.g., in a fluidized bed reactor.

Highlights

The demand for hydrogen has been increasing in the last decades, because it is a component of synthesis gas and used in the hydrogenation processes, and because it is a perfect energy carrier, e.g., in fuel cells (FC)
Approximately 85% of the total hydrogen is produced via the steam reforming of natural gas
Maghsoodi et al [25] have studied the continuous production of carbon nanotubes (CNTs) via the Chemical Vapor Deposition (CVD) of methane over the Fe/MgO catalyst in a fluidized bed reactor at 900 ◦C

Summary

Introduction

The demand for hydrogen has been increasing in the last decades, because it is a component of synthesis gas and used in the hydrogenation processes, and because it is a perfect energy carrier, e.g., in fuel cells (FC). Maghsoodi et al [25] have studied the continuous production of CNTs via the CVD of methane over the Fe/MgO catalyst in a fluidized bed reactor at 900 ◦C. They obtained MWNTs of about 20 nm in size, as well as SWNTs of 1.0–1.2 nm in diameter. There is no data about the production of CNTs in fluidized bed reactors over ceria-zirconia supported metal catalysts. These catalysts are known for being resistant to carbon deposition. Mechanistic studies of these reactions, conducted by tests on a laboratory scale using a “micro-reactor”, have shown the potential of Ni/CeZrO2 for further applications in fluidized bed reactors

Experimental

Catalyst Characterization

CH4 Decomposition to CNTs and H2

Catalyst Regeneration with H2O

Conclusions