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

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.

Highly Active and Stable Ni/La-Doped Ceria Material for Catalytic CO2 Reduction by Reverse Water-Gas Shift Reaction

“…As mentioned earlier in the Introduction, working at high temperatures and using Ni as the metallic phase, the formation of water, produced by the reaction of H atoms coming from the metal particles with the oxygen coming from the partially reduced ceria, seems to be the rate-limiting step for the rWGS reaction, and hydroxyl groups play an important role in water production (rWGS rate-determining step (RDS)). Their concentration was determined under reaction conditions by NAP-XPS, where the O 1s region (Figure d) shows three peaks assigned to lattice oxygen (O L , centered at 529.7 eV), hydroxyl species (OH, at 530.6 eV), and carboxyl species (CO, at 531.8 eV). , It is clear that the Ni0.07/Ce0.9La0.1 sample, which shows a higher Ce 3+ concentration, exhibits a significantly lower amount of OH species than other samples. Therefore, a lower proportion of adsorbed hydroxyl groups under reaction conditions suggests a more favored water formation and desorption, which correlates well with the higher catalytic activity observed for the 10% La-doped catalyst.…”

“…Their concentration was determined under reaction conditions by NAP-XPS, where the O 1s region (Figure 4d) shows three peaks assigned to lattice oxygen (O L , centered at 529.7 eV), hydroxyl species (OH, at 530.6 eV), and carboxyl species (CO, at 531.8 eV). 45,46 It is clear that the Ni0.07/Ce0.9La0.1 sample, which shows a higher Ce 3+ concentration, exhibits a significantly lower amount of OH species than other samples. Therefore, a lower proportion of adsorbed hydroxyl groups under reaction conditions suggests a more favored water formation and desorption, which correlates well with the higher catalytic activity observed for the 10% La-doped catalyst.…”

Nanoshaped Cerium Oxide with Nickel as a Non-Noble Metal Catalyst for CO2 Thermochemical Reactions

“…Currently, one idea for reducing the concentration of CO 2 in the atmosphere is its conversion into products with a high positive value, i.e., chemicals or fuels [ 1 , 2 ]. There is a possibility of thermochemical conversion of CO 2 using solar energy [ 3 ].…”

Cu/Fe3O4 Nanocomposites from Layered Double Hydroxides as Catalysts for Selective Electroreduction of Carbon Dioxide

“…At present, excessive CO 2 emission has caused a variety of serious environmental problems, such as global warming and ocean acidification, which is a severe challenge to the sustainable development of human society . So far, scientists have used various methods, including electrocatalysis, photocatalysis, thermocatalysis, biocatalysis, absorption, and solidification − to convert CO 2 into valuable chemical products, among which electroreduction of CO 2 is an effective method to convert CO 2 into value-added chemicals and promotes carbon neutrality (Scheme ). , Ethanol is an important industrial raw material and a C2 product for CO 2 electroreduction.…”