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

Abstract

The design of an active, effective, and economically viable catalyst for CO 2 conversion into value-added products is crucial in the fight against global warming and energy demand. We have developed very efficient catalysts for reverse water-gas shift (rWGS) reaction. Specific conditions of the synthesis by combustion allow the obtention of macroporous materials based on nanosized Ni particles supported on a mixed oxide of high purity and crystallinity. Here, we show that Ni/La-doped CeO 2 catalysts�with the "right" Ni and La proportions�have an unprecedented catalytic performance per unit mass of catalyst for the rWGS reaction as the first step toward CO 2 valorization. Correlations between physicochemical properties and catalytic activity, obtained using a combination of different techniques such as X-ray and neutron powder diffraction, Raman spectroscopy, in situ near ambient pressure X-ray photoelectron spectroscopy, electron microscopy, and catalytic testing, point out to optimum values for the Ni loading and the La proportion. Density functional theory calculations of elementary steps of the reaction on model Ni/ ceria catalysts aid toward the microscopic understanding of the nature of the active sites. This finding offers a fundamental basis for developing economical catalysts that can be effectively used for CO 2 reduction with hydrogen. A catalyst based on Ni 0.07 / (Ce 0.9 La 0.1 O x ) 0.93 shows a CO production of 58 × 10 −5 mol CO •g cat −1•s −1 (700 °C, H 2 /CO 2 = 2; selectivity to CO > 99.5), being stable for 100 h under continuous reaction.

Comprehensive Density Functional and Kinetic Monte Carlo Study of CO2 Hydrogenation on a Well-Defined Ni/CeO2 Model Catalyst: Role of Eley–Rideal Reactions

“…We suggest that these differences are due to the different initial and final states used and to the different computational methodology used for the calculations. In fact, Alvarez-Galvan et al reported a CO 2 dissociation energy barrier of 0.75 eV, which nicely agrees with our calculated value of 0.77 eV. Moreover, they also found a barrierless H 2 dissociation reaction also in line with our results.…”

“…The difference is clearly due to the different Ni atom in which H 2 adsorbs as well as to the lack of the ZPE term. For instance, in this study, the molecular H 2 adsorption energy with and without the ZPE term is −0.63 and −0.75 eV, respectively, the latter being closer to the value reported by Alvarez-Galvan et al Moreover, additional deviations can arise from the inclusion or not the contribution of long-range dispersion interactions, which have been included in our calculations via the Grimme’s D3 approach, while it seems that this is not the case in the literature values. Finally, Lustemberg et al reported adsorption energies of −0.93 and −0.24 eV for H 2 O and CH 4 , respectively, which agree with our reported values.…”

“…Moreover, our values include the ZPE term, while it does not seem to be included in the commented previous works. Alvarez-Galvan et al . also reported a molecular H 2 adsorption energy of −0.95 eV, which again is slightly larger than the present value of −0.63 eV.…”

“…A careful comparison between present and previous values helps in understanding the origin of the differences in adsorption energy. For instance, we have found a CO 2 structure that is bent to the surface; hence, featuring a higher interaction with the surface that can explain the higher adsorption energy, we have found with respect to the study of Alvarez-Galvan et al 46 Regarding the latter study by Zhang et al, 27 the differences are smaller�less than 0.2 eV�and can be attributed to the different computational code used and the different methodology used in the calculations. Moreover, our values include the ZPE term, while it does not seem to be included in the commented previous works.…”

Ionic Nickel Embedded in Ceria with High Specific CO2 Methanation Activity

“…[10][11][12] The combination of the above mentioned characteristics established CeO 2 -supported Ni catalysts as one of the most studied and promising candidates for the CO 2 methanation reaction. [13,14] Although the factors controlling the performance of Ni/ CeO 2 methanation catalysts are far from being completely understood, there is consensus that the Ni particle size, [9,[15][16][17] the interaction at the Ni-CeO 2 interphase [16,18,19] and the reducibility of ceria [20,21] are the most critical features of the catalyst. Despite the ongoing debate on the optimal Ni particle size, [8,9,[15][16][17] there is general belief that metallic Ni is essential for CO 2 methanation, while ionic Ni deteriorates the catalytic reaction.…”