The effects of stoichiometry on the properties of exsolved Ni‐Fe alloy nanoparticles for dry methane reforming

Abstract

The dry reforming of methane has received notable attention as a chemical process to convert natural gas into value-added chemicals and fuels. Ni-based exsolution catalysts using perovskite oxides supports have been used for their attractive sinterresistance and coke-resistance properties. The perovskite oxide in itself has unique defect chemistry that can be used to manipulate and control the properties of the catalyst nanoparticles exsolved on the surface, therefore influencing both the nanoparticle and support characteristics. In this study, the La:Fe ratio of Ni-doped LaFeO 3 was used to manipulate and control the properties of exsolved Ni-Fe alloy nanoparticles. The Ni-Fe nanoparticles consisted of different sizes ranging from 10 to 380 nm. Temperature programmed surface reaction studies along with materials characterization with SEM, STEM-HAADF, XRD, and BET showed that the Ni-Fe nanoparticles from different solid precursors have the same active sites for methane activation but differ in performance and stability because of size effects, metalsupport strength, composition and support basicity. A mechanism is proposed to decipher the merits of the Ni-Fe nanoparticles with the best activity, selectivity, and stability in this study.

Exsolution of Embedded Ni–Fe–Co Nanoparticles: Implications for Dry Reforming of Methane

“…We examined the notion of bulk defect manipulation of perovskite oxide precursors to change the alloy composition, size, and shape of exsolved NiFe nanoparticles for DRM. 31 We found that the B-site metal redox properties can change nanoparticle formation and bulk crystal structure dynamics, influencing catalyst performance. Additionally, we uncovered a limitation in the coke resistance properties of the perovskite precursors where large NiFe nanoparticles showed considerable graphitic coke formation that limited the catalyst performance.…”

LaNixFe1–xO3−δ as a Robust Redox Catalyst for CO2 Splitting and Methane Partial Oxidation

“…These two peaks correspond to the reduction of metal cations. The first peak is likely to be the reduction of Fe 3+ to Fe 2+ and Ni 3+ to Ni 2+ , whereas the second peak can be assigned to the further reduction to metallic phases . CGCO, on the other hand, is hardly reducible at temperatures less than 800 °C.…”

“…The first peak is likely to be the reduction of Fe 3+ to Fe 2+ and Ni 3+ to Ni 2+ , whereas the second peak can be assigned to the further reduction to metallic phases. 41 CGCO, on the other hand, is hardly reducible at temperatures less than 800 °C. However, the synergistic effect of the LNF/CGCO composite would facilitate its reduction.…”

Synthesizing High‐Volume Chemicals from CO2 without Direct H2 Input

“…By controlling exsolution conditions, the size of the metal particles can be minimized to (i) maximize the dispersion of active sites, (ii) enhance synergistic interactions between the metal and the support, and (iii) suppress carbon deposition. [91,226] The most commonly studied perovskite-based dry reforming catalyst is LaNiO 3 , [92] whose performance can be further optimized through A-site and B-site substitution. For example, a post-exsolved LaNi 0.8 Mn 0.2 O 3 catalyst showed enhanced activity attributed to the MnO phase, which promoted CO 2 activation.…”

“…The post‐exsolution oxide structures act as supports as well as promoters for CO 2 activation. By controlling exsolution conditions, the size of the metal particles can be minimized to (i) maximize the dispersion of active sites, (ii) enhance synergistic interactions between the metal and the support, and (iii) suppress carbon deposition [91,226] …”