Abstract

Sub-nanometer zeolite 13X-supported Ni-ceria catalysts were synthesized for CO2 methanation. XRD and SEM results show the structure and morphology of 13X zeolite after impregnation and calcination. Ce loading affected the catalysts’ metal dispersion, reducibility, basicity and acidity, and thence their activity and selectivity. STEM-EDX elemental mappings showed that Ce and Ni are predominantly highly dispersed. Ce has a positive effect on the reduction of NiO and leads to a relatively high number of medium basic sites with a low Ce loading. Highly stable 5%Ni2.5%Ce13X had high activity and nearly 100% CH4 selectivity in CO2 methanation at 360 °C, which is mainly due to the high dispersion of metals and relatively high amount of medium basic sites. It can be inferred that this catalyst synthesis strategy has great potential for good catalyst dispersion, since metal uptake by the zeolite is selective for the metal citrate complexes in solution.

Highlights

  • Sorption-enhanced CO2 methanation has attracted significant attention from researchers in recent years due to its potential in future processes for energy storage and use [1,2]

  • We investigated the Ni/change after Ni (Ce) ratio effect for Ni:Ce 13X zeolite catalysts with Ce loading varying from 0 to 10 wt.% and Ni loading fixed at 5 wt. %

  • The calcined catalysts were characterized by Xray powder diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX), transmission electron mi­ croscopy (TEM), scanning transmission electron microscopy equipped with energy-dispersive X-ray spectroscopy (STEM-EDX), X-ray photo­ electron spectroscopy (XPS), hydrogen-temperature programmed reduction (H2-TPR), Fourier transform infrared (FT-IR), CO2-tempera­ ture programmed desorption (CO2-TPD), and pyridine-FTIR

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Summary

Introduction

Sorption-enhanced CO2 methanation has attracted significant attention from researchers in recent years due to its potential in future processes for energy storage and use [1,2]. When traditional methods are used to prepare catalysts [1,2,4], the dispersion of Ni on zeolite is typically far from single-atom or sub-nanometer. This de­ creases the activity of the active metal, and increases its inventory. Few or single-atom based bi-functional materials, i.e. having catalytic plus sorption properties, are a promising option (Fig. 1), because they have high activity and should largely retain their water-adsorption capacity by loading only a very limited amount of metal into the support material. We describe a facile metal-complex precursor strategy to prepare sub-nanometer Ni clusters, or even single-atoms, to be used in combi­ nation with the sorbent properties to yield a bi-functional material with great potential for heterogeneous catalysis.

Catalyst preparation
Catalyst characterization
Catalyst structure and surface properties
Evaluation of catalytic properties in methanation using a fixed-bed reactor
Conclusions

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