Effect of Support and Chelating Ligand on the Synthesis of Ni Catalysts with High Activity and Stability for CO2 Methanation

Vetrivel Shanmugam,Stefan Neuberg,Gunther Kolb,Ralf Zapf,Helmut Pennemann

doi:10.3390/catal10050493

Vetrivel Shanmugam, Stefan Neuberg + Show 3 more

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https://doi.org/10.3390/catal10050493

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Abstract

Carbon dioxide methanation was carried out over Ni-based catalysts on different supports and chelating ligands in microreactors. To investigate the influence of chelating ligands and supports, the Ni catalysts were prepared using different support such as CeO2, Al2O3, SiO2, and SBA-15 by a citric acid (CA)-assisted impregnation method. The properties of the developed catalysts were studied by X-ray diffraction (XRD), Transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS) measurement, and the results show that the addition of CA in the impregnation solution improved the dispersion, refines the particle size, and enhanced the interaction of nickel species. The catalytic performance of the developed Ni catalysts were evaluated by CO2 methanation in microreactors in the temperature range of 275 °C–375 °C under 12.5 bar pressure. All the catalysts exhibit high CO2 conversion and extremely high selectivity to methane. However, the catalysts prepared via CA-assisted method exhibited excellent activity and stability, compared with Ni catalysts prepared by a conventional impregnation method, which could be attributed to highly dispersed nickel particles with strong metal–support interaction. The activity of CO2 methanation followed the order of Ni/CeO2-CA > Ni/SBA-15-CA > Ni/Al2O3-CA > Ni/SiO2-CA > Ni/CeO2. The Ni/CeO2 catalysts have also been prepared using different chelating ligands such as ethylene glycol (EG), sucrose (S), oxalic acid (OA) and ethylene diamine tetra acidic acid (EDTA). Among the tested catalysts prepared with different support and chelating ligands, the Ni/CeO2 catalyst prepared via CA-assisted method gave superior catalytic performance and it could attain 98.6% of CO2 conversion and 99.7% methane selectivity at 325 °C. The partial reduction of the CeO2 support generates more surface oxygen vacancies and results in a high CO2 conversion and methane selectivity compared with other catalysts. The addition of CA as promoter favored the synergistic effect of Ni and support, which led to high dispersion, controls the size, and stabilizes the Ni nanoparticles. Furthermore, the Ni/CeO2-CA catalyst yields high CO2 conversion in a time-on-stream study due to the ability of preventing the carbon deposition and sintering of Ni particles under the applied reaction conditions. However, the Ni/Al2O3-CA and Ni/SBA-15-CA catalysts showed stable performance for 100 h of time on stream.

Highlights

Since the CO2 emissions into the atmosphere cause greenhouse effects and global warming, its fixation has received much attention in recent years and has become a world challenge and Catalysts 2020, 10, 493; doi:10.3390/catal10050493 www.mdpi.com/journal/catalystsCatalysts 2020, 10, 493 priority [1]
We introduced sucrose as chelating ligand, which contributes majorly to the distribution of Ni species by preventing their sintering on SBA-15 silica support [42]
Ni catalysts supported on different supports were prepared by chelating ligand-assisted impregnation method and their catalytic activity was investigated by CO2 methanation at different temperatures

Summary

Introduction

Since the CO2 emissions into the atmosphere cause greenhouse effects and global warming, its fixation has received much attention in recent years and has become a world challenge and Catalysts 2020, 10, 493; doi:10.3390/catal10050493 www.mdpi.com/journal/catalystsCatalysts 2020, 10, 493 priority [1]. Since the CO2 emissions into the atmosphere cause greenhouse effects and global warming, its fixation has received much attention in recent years and has become a world challenge and Catalysts 2020, 10, 493; doi:10.3390/catal10050493 www.mdpi.com/journal/catalysts. In recent years, increased research efforts have been dedicated to the chemical conversion of CO2 into useful chemicals such as methane, methanol, ethanol, and dimethyl ether through catalytic hydrogenation [14]. CO2 methanation is considered to be one of the most promising ways of transforming CO2 into methane, which is an important chemical feedstock as well as a fuel for power generation by gas turbines. The amount of catalyst which can be incorporated into such a reactor is limited. The development of catalysts of high activity is the key factor for the CO2 methanation reaction at low temperature [17,18]

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