Nanostructure effects on the kinetics and deactivation at reactions over multifunctional catalysts

•Catalyst deactivation rate depends on the size of supported metal particles.•Nanosized metal particles are highly sensitive for poisoning and deactivation.•Multi-centered and single active sites differ in vulnerability level on coking.•Coking lowers probability for site ensembles catalyzing structure-sensitive routes.•Active sites edging coke have reduced potential to favor structure-sensitive steps.

This study brings into focus some nanostructure-size effects on the deactivation kinetics at reactions over supported multifunctional catalysts. The active phase dispersion as nano-sized islands on the support predetermines diversities in the action of active sites depending on their location and structure. In view of this, the applied approach assumes participation of active site types differing by coordination, configuration and contribution to various reaction routes. The suggested model concerns regularities associated with the availability of active surface atoms in proper arrangements which facilitate structure-sensitive reactions. Problems linking the vulnerability of active sites with their geometry and structure are put to discussion. Furthermore, the model relates the probabilities for action of different site types to the size of active-phase islands. The effect of site blockage on the probabilities for existence of multi-site active centers (catalytic clusters) facilitating structure-sensitive reactions is explored. The performed analysis points out that, when matter concerns reactions facilitated by multi-centered active sites, two distinct reasons can be specified, by virtue of which coke species may affect the activity of catalytic clusters: (i) canceling the action of partially or totally coke-covered cluster configurations and (ii) reducing the capability of the adjacent active atoms to construct multi-centered active configurations.

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