Robust and Coke-free Ni Catalyst Stabilized by 1–2 nm-Thick Multielement Oxide for Methane Dry Reforming

Abstract

Methane dry reforming, co-converting greenhouse gases CH 4 and CO 2 into chemically active syngas (H 2 /CO), affords a promising route for producing chemicals and fuels from carbon resources. Ni catalysts are the most active for this reaction but suffer from the dilemma of rapid deactivation caused by metal sintering at higher temperatures (>973 K) or coke accumulation at relatively lower temperatures (673−973 K). Here, we report a catalyst configurationNi particles (15 nm) confined by a 1−2 nm-thick multielement-oxide (MEO) layerallows a stable operation at 873−1073 K with a stoichiometric CH 4 /CO 2 ratio of 1.0, that is, the severe conditions for catalyst deactivation but of industrial interest for process efficiency and atomic economy. The in situ-evolved MEO layer resembles the property of high-entropy oxide, which stabilizes the Ni particles with appropriate size and high-index facets, even at 1173 K. Meanwhile, in situ TEM under near atmospheric pressure combining intelligent gravity analysis (IGA)-mass spectrometry (MS) characterizations prove that this unique structure balanced the activation of CH 4 and CO 2 . Thus, the lifetime of the catalyst has been efficiently prolonged with nearly coke-free operations, even at 873 K, the most severe coking temperature. This high-entropy design and stabilization effect offers a facile strategy to precisely fabricate active and robust metal catalysts with wide operation temperatures for many challenging reactions.

A review on catalyst development for conventional thermal dry reforming of methane at low temperature

“…Except for the core-shell encapsulation configuration, some studies also tried to coat some thin metal oxide layers to stabilize the Ni particles on support. [100,107] He et al coated the Si layer on Ni/Mg-Al hydrotalcite nanosheets, and a 1$2 nm thin layer was formed outside the Ni sites containing Si, Mg, and Al after H 2 reduction. [100] And Jin et al deposited the ZrO 2 film via atomic layer deposition (ALD) on the Ni/Al 2 O 3 catalyst.…”

“…[100,107] He et al coated the Si layer on Ni/Mg-Al hydrotalcite nanosheets, and a 1$2 nm thin layer was formed outside the Ni sites containing Si, Mg, and Al after H 2 reduction. [100] And Jin et al deposited the ZrO 2 film via atomic layer deposition (ALD) on the Ni/Al 2 O 3 catalyst. [107] In these studies, with engineering-confined strategies, the catalyst showed improved coke resistance and less tendency of Ni sintering and migrating.…”

“…[26] The utilization of the Ni complex contributed to well-dispersed Ni sites on the support with a size of [48,68] F I G U R E 2 2 (A) Schematic illustration of a thin layer of multielement on the Ni/Mg-Al hydrotalcite catalyst. Reproduced with permission from He et al [100] Copyright 2021 American Chemical Society. (B) Synthesis strategy of Ni/Al 2 O 3 with the ZrO 2 film.…”

Promoting Methane Dry Reforming over Ni Catalysts via Modulating Surface Electronic Structures of BN Supports by Doping Carbon

“…In the meantime, the unsaturated coordination sites, such as edge, corner, and vertex sites, with higher catalytic activity on the Ni particles are lost if the particle agglomeration happened, which in turn affects the catalytic activity . To overcome these drawbacks, several approaches have been explored as follows: (i) modification of active sites by adding the secondary metal to suppress the decomposition of CH 4 , , (ii) utilization of basic or redox supports to facilitate the activation of CO 2 to gasify the deposited carbon species, − and (iii) construction of confinement structures to immobilize Ni nanoparticles (NPs) to protect the active species from agglomeration during the MDR process. − …”

Coking- and Sintering-Resistant Ni Nanocatalysts Confined by Active BN Edges for Methane Dry Reforming

“…The stoichiometry syngas produced in MDR is suitable for preparing high value-added chemicals via Fischer–Tropsch synthesis, which is also crucial for mitigating greenhouse gas emissions. − Considering the low cost and comparable activity with noble metals, Ni-based catalysts have become one of the most promising choices for MDR. However, coking and sintering of active metal causes the serious deactivation of Ni-based catalysts during the MDR process. − Traditional strategies to solve these problems are controlling the Ni particle size via well-confined structured catalysts, − utilizing basic supports to enrich the surface oxygen vacancies, − and adding the secondary metals to increase the dispersion of Ni particles. − Most of the strategies mentioned in the literature utilize metal oxides as the support of catalysts, which can promote the catalytic activity significantly. Nevertheless, the coking issue is still a formidable one to eliminate.…”