The physical chemistry and materials science behind sinter-resistant catalysts

Abstract

Catalyst sintering, a main cause of the loss of catalytic activity and/or selectivity at high reaction temperatures, is a major concern and grand challenge in the general area of heterogeneous catalysis. Although all heterogeneous catalysts are inevitably subjected to sintering during their operation, the immediate and drastic consequences can be mitigated by carefully engineering the catalytic particles and their interactions with the supports. In this tutorial review, we highlight recent progress in understanding the physical chemistry and materials science involved in sintering, including the discussion of advanced techniques, such as in situ microscopy and spectroscopy, for investigating the sintering process and its rate. We also discuss strategies for the design and rational fabrication of sinter-resistant catalysts. Finally, we showcase recent success in improving the thermal stability and thus sinter resistance of supported catalytic systems.

Complex oscillatory decrease with size in diffusivity of {100}-epitaxially supported 3D fcc metal nanoclusters

“…Smoluchowski Ripening (SR) involving diffusion and coalescence of supported 3D metal nanoclusters (NCs), also known as Particle Migration & Coalescence (PMC), is of central importance as a pathway for catalyst degradation. [1][2][3][4][5] Classic studies have analyzed SR kinetics which is controlled by the sizedependence of NC diffusivity. 1,2 Consequently, there has been sustained interest in the variation of the NC diffusion coefficient, D N , with size N (in atoms).…”

Recover the activity of sintered supported catalysts by nitrogen-doped carbon atomization

“…upported metal catalysts can efficiently accomplish many important industrial applications in heterogeneous catalysis, including the production of chemicals 1 , pharmaceuticals 2 and clean fuels 3 , and the purification of vehicle emissions [4][5][6][7] . However, most of the supported catalysts suffer from sintering, which significantly decrease their active surface areas, stability, and shut down the catalytic steps 6,[8][9][10][11] . The sintering is usually accelerated above the Tammann temperature (half of the melting point in absolute units) 4,12 , involving the emission of mobile species from small particles and their capture by large particles (Ostwald ripening), or particles migration and coalescence 7,8,12 .…”

Multiscale simulation on thermal stability of supported metal nanocatalysts

“…An increase of chemical potential of the atom on a metal NP leads to a greater thermodynamic driven force towards sintering, and thus acceleration of sintering . The sintering of NPs can be roughly understood in terms of two mechanisms: (a) Ostwald ripening: the NPs adhere strongly to the surface, which make atomic transfer between NPs more favorable and (b) Particle migration and coalescence: the NPs adhere weakly to the surface, which permit them to diffuse across it and to coalesce on contact . Ostwald ripening involves inter‐particle transport of mobile species, with larger NP growing at the expense of smaller one due to surface energy differences.…”

“…The inter‐particle sintering process often occurs through two above‐mentioned pathways: (a) Particle migration and coalescence and (b) Ostwald ripening. In the experiment, differentiation of these two mechanisms is not easy as this process may be dominated by both of them either simultaneously or alternatively …”

“…The accuracy of theoretical calculations for heterogeneous catalytic behaviors has improved greatly to match some experimental findings or obtain a reasonable interpretation of experimental results. Usually, the activity and thermal stability exert an influence on each other, the most active atoms on NPs with low coordination numbers are also the most mobile sites for the initiation of sintering . Understanding the structural influence on the thermal stability is crucial to seek the balance between high stability and catalytic activity for the rational design of catalysts.…”