Exsolution of Metallic Ru Nanoparticles from Defective, Fluorite-Type Solid Solutions Sm₂Ru_xCe_2–xO₇ To Impart Stability on Dry Reforming Catalysts

Abstract

A key challenge in the catalytic conversion of CH 4 and CO 2 into a synthesis gas (CO and H 2 ) via the dry reforming of methane (DRM) is the development of stable catalysts. We demonstrate that the reductive exsolution of metallic Ru from fluorite-type solid solutions Sm 2 Ru x Ce 2−x O 7 (x = 0, 0.1, 0.2, 0.4) yields catalysts with high activity and remarkable stability for the DRM. The catalysts feature Ru(0) nanoparticles about 1−2 nm in diameter that are uniformly dispersed on the surface of the resulting oxide support. The exsolved material was investigated by synchrotron X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS at Ru, Sm, and Ce K-edges), Raman spectroscopy, and transmission electron microscopy. In situ XAS-XRD experiments revealed that the exsolution of metallic ruthenium is accompanied by a rearrangement of the oxygen vacancies within the lattice. The catalysts derived through exsolution outperform (stable over 4 days) the reference catalysts prepared by wetness impregnation and sodium borohydride reduction. The superior performance of the exsolved catalysts is explained by their high resistance to sintering-induced deactivation owing to the stabilizing metal−support interaction in this class of materials. It is also demonstrated that the Ru nanoparticles can undergo redissolution (in air at 700 °C)−exsolution cycles.

Molybdenum carbide and oxycarbide from carbon-supported MoO3 nanosheets: phase evolution and DRM catalytic activity assessed by TEM and in situ XANES/XRD methods

“…53 To obtain information about the state of the annealed material at the specific temperatures and gas atmospheres, we turned to in situ experimentation and followed the CHR process (d-MoO 3 /C → β-Mo 2 C/C) by a combined in situ XANES/ XRD experiment. 18,40,41 The XANES spectra were collected at the Mo K-edge during annealing of d-MoO 3 /C from 50 to 750°C (highest attainable temperature of the set up) under He and 50% H 2 /He at 750°C (total flow rates of 5 and 10 mL min −1 , respectively), while XRD patterns were collected at 50, 400 and 750°C during the same experiment. For the latter temperature, data were collected under a flow of pure helium or 50% H 2 /He.…”

“…Here, we studied the CHR reaction of two dimensional delaminated MoO 3 nanosheets (d-MoO 3 ) supported on carbon spheres, which served as carbon source for carburization and also provided a suitable morphological and phase contrast for transmission electron microscopy. Combination of in situ XANES/XRD analysis 18,40,41…”

Exploring the Stability of Fe–Ni Alloy Nanoparticles Exsolved from Double-Layered Perovskites for Dry Reforming of Methane

“…Since the nanoparticles grow from inside, in contrast to the deposited particles, they remain anchored to the oxide surface, which provides high stability against sintering and coking (Figure 1) [7]. Most works have been focused on nanoparticle exsolution on perovskites [2,4,5], although lately, exsolution has also been observed on other oxides like in fluorite structures [8,9]. Perovskites, of the ABO3 formula (with A = La, Sr, Ca, Ba, and B, a transition metal cation) have been widely explored as catalysts for DMR based on their…”

Boosting methane partial oxidation on ceria through exsolution of robust Ru nanoparticles

“…The fact that the nanoparticles are socketed into the oxide surface imparts beneficial effects in terms of stability, avoiding nanoparticle sintering 23 . For that reason, exsolution has gained considerable attention in the field of solid oxide fuel cells and electrolyzers 24,25 , and more recently its application has been found to be promising in methane reforming reactions [26][27][28][29] . For instance, Kousi and co-workers obtained Ni exsolved and submerged nanoparticles on La 0.8 Ce 0.1 Ni 0.4 Ti 0.6 O 3 with synergistically enhance the oxygen supply capacity.…”