Chemical and Thermal Sintering of Supported Metals with Emphasis on Cobalt Catalysts During Fischer–Tropsch Synthesis

Abstract

This comprehensive critical review combines, for the first time, recent advances in nanoscale surface chemistry, surface science, DFT, adsorption calorimetry, and in situ XRD and TEM to provide new insights into catalyst sintering. This work provides qualitative and quantitative estimates of the extent and rate of sintering as functions of nanocrystal (NC) size, temperature, and atmosphere. This review is unique in that besides summarizing important, useful data from previous studies, it also advances the field through addition of (i) improved or new models, (ii) new data summarized in original tables and figures, and (iii) new fundamental perspectives into sintering of supported metals and particularly of chemical sintering of supported Co during Fischer–Tropsch synthesis. We demonstrate how the two widely accepted sintering mechanisms are largely sequential with some overlap and highly NC-size dependent, i.e., generally, small NCs sinter rapidly by Ostwald ripening, while larger NCs sinter slowly by crystallite migration and coalescence. In addition, we demonstrate how accumulated knowledge, principles, and recent advances, discussed in this review, can be utilized in the design of supported metal NCs highly resistant to sintering. Recommendations for improving the design of sintering experiments and for new research are addressed.

Stability of Cobalt Particles In and Outside HZSM‐5 under CO Hydrogenation Conditions Studied by ex situ and in situ Electron Microscopy

“…Kristamurthy et al reported Ostwald ripening on planar Co/SiO 2 catalysts under FT conditions as a rapid sintering mechanism for small cobalt nanoparticles, [61] while larger nanoparticles are reported to sinter more slowly by crystallite migration and coalescence. [26] The broad range of behaviors, mainly affecting the disintegrated particles, further indicates different physical environments present for the visible particles within the regions of interest. Furthermore, there were additional particles noticeable (blue circles in Figure 5a, e), showing clearly smaller diameters than the cobalt particles, appearing to decompose after 66 min at 700°C.…”

“…[18][19][20] Importantly, many catalysts suffer from deactivation under reaction conditions, due to various mechanisms including sintering at high temperatures and via carbonyl formation, as well as water induced re-oxidation or formation of carbon deposits. [21][22][23][24][25] The group of Bartholomew [26] recently summarized the state of knowledge on deactivation of cobalt catalysts for FT synthesis comprehensively and particularly pointed out that "in situ experimental methods for measuring NC size and size distribution with time on stream" are required for "further progress in the development of more sinterresistant Co catalysts". Those methods are performed preferably as close as possible to typical operating conditions.…”

Green production of hydrogen-doped faceted cobalt microcrystals using water-assisted molten salt electro-reduction method

“…Moreover, it is known that Co is an effective catalyst, for which the catalytic reactivity is facet-dependent and can be highly promoted in faceted crystals. 62,63 The physical and mechanical properties of Co crystals produced by the molten salt method are interesting to study in future works.…”

Rare‐Earth‐Based Metal–Organic Frameworks as Multifunctional Platforms for Catalytic Conversion

“…For instance, Cobased catalysts were employed to catalyze the Fisher-Tropsch (F-T) process, which accelerated industrialization of F-T reaction. [1] Most of the modern chemical and petroleum refinery industries have already applied catalytic processes. [2] Metal-organic frameworks (MOFs) are kind of coordination polymers with a 3D pore structure consisting of metal nodes and organic linkers, being developed rapidly within the last decade.…”