Thermocatalytic CO2 Conversion over a Nickel-Loaded Ceria Nanostructured Catalyst: A NAP-XPS Study.

Adrián Barroso-Bogeat,Juan José Pérez-Sagasti,José María Pintado,Carlos Escudero,Ginesa Blanco,Eric Pellegrin,Facundo C Herrera

doi:10.3390/ma14040711

Abstract

Despite the increasing economic incentives and environmental advantages associated to their substitution, carbon-rich fossil fuels are expected to remain as the dominant worldwide source of energy through at least the next two decades and perhaps later. Therefore, both the control and reduction of CO2 emissions have become environmental issues of major concern and big challenges for the international scientific community. Among the proposed strategies to achieve these goals, conversion of CO2 by its reduction into high added value products, such as methane or syngas, has been widely agreed to be the most attractive from the environmental and economic points of view. In the present work, thermocatalytic reduction of CO2 with H2 was studied over a nanostructured ceria-supported nickel catalyst. Ceria nanocubes were employed as support, while the nickel phase was supported by means a surfactant-free controlled chemical precipitation method. The resulting nanocatalyst was characterized in terms of its physicochemical properties, with special attention paid to both surface basicity and reducibility. The nanocatalyst was studied during CO2 reduction by means of Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS). Two different catalytic behaviors were observed depending on the reaction temperature. At low temperature, with both Ce and Ni in an oxidized state, CH4 formation was observed, whereas at high temperature above 500 °C, the reverse water gas shift reaction became dominant, with CO and H2O being the main products. NAP-XPS was revealed as a powerful tool to study the behavior of this nanostructured catalyst under reaction conditions.

Highlights

Since the start of the Industrial Revolution in 1750, carbon-rich fossil fuels have become essential raw materials for the production of energy and of commodity chemicals [1]
Ceria nanocubes were employed as support, while the nickel phase was supported by means a surfactant-free controlled chemical precipitation method
A basic structural and textural characterization of the as-prepared CeO2 NCs and 5Ni-CeO2 NCs samples was performed by X-ray diffraction (XRD) and N2 physical adsorption, respectively

Summary

Introduction

Since the start of the Industrial Revolution in 1750, carbon-rich fossil fuels (i.e., oil, coal, and natural gas) have become essential raw materials for the production of energy and of commodity chemicals [1]. Despite the obvious environmental benefits and increasing governments’ economic incentives associated with their substitution, these fuels are foreseen to remain as the dominant primary energy source in the medium-term future [2] Such an extensive use, together with the still low efficiency of the vast majority of energetic processes, has been causing a steady rise in the atmospheric levels of CO2, the major human-related greenhouse gas, during the past two centuries and especially in the second half of the 20th century [1,3]. More intense research efforts are still required in order to make these reactions sustainable in large-scale processes [11], and a great deal of work has been done in testing metal/reducible oxides catalysts Pathways for these reactions are not yet clear, there is a certain agreement concerning the way both the supported metal phase and the oxide are involved in the reaction. H2 activation is performed by the supported metal, whereas the support provides oxygen vacancies to activate CO2 [14,15,16]

Methods

Results

Conclusion