Dynamic restructuring of supported metal nanoparticles and its implications for structure insensitive catalysis

Abstract

Some fundamental concepts of catalysis are not fully explained but are of paramount importance for the development of improved catalysts. An example is the concept of structure insensitive reactions, where surface-normalized activity does not change with catalyst metal particle size. Here we explore this concept and its relation to surface reconstruction on a set of silica-supported Ni metal nanoparticles (mean particle sizes 1–6 nm) by spectroscopically discerning a structure sensitive (CO2 hydrogenation) from a structure insensitive (ethene hydrogenation) reaction. Using state-of-the-art techniques, inter alia in-situ STEM, and quick-X-ray absorption spectroscopy with sub-second time resolution, we have observed particle-size-dependent effects like restructuring which increases with increasing particle size, and faster restructuring for larger particle sizes during ethene hydrogenation while for CO2 no such restructuring effects were observed. Furthermore, a degree of restructuring is irreversible, and we also show that the rate of carbon diffusion on, and into nanoparticles increases with particle size. We finally show that these particle size-dependent effects induced by ethene hydrogenation, can make a structure sensitive reaction (CO2 hydrogenation), structure insensitive. We thus postulate that structure insensitive reactions are actually apparently structure insensitive, which changes our fundamental understanding of the empirical observation of structure insensitivity.

Resolving the Effect of Oxygen Vacancies on Co Nanostructures Using Soft XAS/X-PEEM

“…This is particularly important for FTS because there is a strong size dependency on catalyst performance and stability, 29 , 30 as well as for other well-known structure-sensitive catalytic reactions, such as CO 2 hydrogenation. 31 , 32 In this work, we have applied a combined surface-sensitive spectroscopic and microscopic method which is capable of probing the metal–support interface so as to be able to probe and determine the surface O vac promotional effect on the reduction behavior of supported Co 3 O 4 NPs. To this end, a two-dimensional (2D) Co/TiO 2 sample was prepared by depositing on rutile (110) presynthesized Co 3 O 4 NPs, exhibiting a range (6–18 nm) of particle sizes relevant to FTS.…”

“…Interestingly, it has previously been reported that oxygen vacancies (O vac ) or the presence of Ti 3+ on TiO 2 surfacescreated by thermal annealing or plasma treatment, , enhance metal oxide reducibility in TiO 2 supported catalysts, proposed to occur through the capture of oxygen-containing species via oxygen spillover. , Parameters such as support particle size and morphology have been shown to influence O vac formation and reducibility of NPs, , however, to date there is not a clear understanding of the promotional effect of O vac as a function of the supported metal (oxide) NP size. This is particularly important for FTS because there is a strong size dependency on catalyst performance and stability, , as well as for other well-known structure-sensitive catalytic reactions, such as CO 2 hydrogenation. , In this work, we have applied a combined surface-sensitive spectroscopic and microscopic method which is capable of probing the metal–support interface so as to be able to probe and determine the surface O vac promotional effect on the reduction behavior of supported Co 3 O 4 NPs. To this end, a two-dimensional (2D) Co/TiO 2 sample was prepared by depositing on rutile (110) presynthesized Co 3 O 4 NPs, exhibiting a range (6–18 nm) of particle sizes relevant to FTS.…”

Heterogeneous Catalysts toward CO2 Hydrogenation for Sustainable Carbon Cycle

“…(b) Size effect on the activity over Ni particles. Reproduced from ref . Copyright 2021 The Authors under Creative Commons CC BY license.…”

Elucidation of Cu–Zn Surface Alloying on Cu(997) by Machine-Learning Molecular Dynamics

“…In fact, the STM experiments by Sano et al indicated that most of the Zn atoms are eventually substituted homogeneously into the terrace rather than localized at the step edge under vacuum conditions . Further, it is well known that the Cu step adatom migrates intensively along the step edge, resulting in step fluctuation even at room temperature. , The assumption of a perfect step edge will also become invalid if the presence of adsorbates induces the reconstruction of the surface, the phenomenon that has been evidenced by various studies. − Therefore, the understanding of the realistic catalyst’s surface is essential to provide a good assumption of the surface model and better interpretation of experimental data.…”