Particle size effect and its influence on the adsorbed complex stability

Abstract

The work had focused on the research area of structural effects, primarily the effect of the particle size of the active metal on the stability of an adsorbed complex, i.e. the key structure produced during a reactant transformation to a product on the surface of heterogeneous catalysts. The obtained results show that significant changes occur in the stability of adsorbed complexes of unsaturated alcohols according to changes in the particle size of the active metal of platinum catalysts. The work had engaged in the research area of structural effects and its influences on the course of heterogeneously catalyzed hydrogenation of alkenic substances in the liquid phase on platinum catalysts. The combination of experimental (kinetic method and physical–chemical characterization) and theoretical methods (calculations based on molecular modeling) was utilized in order to efficiently study these effects having impact both on the side of model substrates (alkenic alcohols differing in the location of C C bond and OH group) and the catalyst active site. This approach allowed comparing the stability of an absorbed complex of all selected model substrates, i.e. the key structure produced during the reactant transformation to a product on the surface of heterogeneous catalysts. The main attention was dedicated to the effect of the particle size of the catalyst active metal that took a significant part in the stability change of the adsorbed complexes of the model substrates as well as the utilization of findings acquired from appositely selected theoretical models to explain this change. The acquired results inferred that it is possible to use the frontier orbitals model to describe the interaction between the active site represented by particles with D > 5–6 nm and C C bond of the alkenic alcohols. The formed adsorbed complex demonstrated larger stability with hept-1-en-4-ol (β-position of the OH group to the C C bond) substrate in comparison to pent-1-en-3-ol (α-position of the OH group to the C C bond). The model of a planar metal complex with the substrate as its ligand appeared to be promising in the case of hydrogenation proceeding on small particles ( D < 5–6 nm). The stability of the complexes with α- and β-hydroxyalkenes demonstrated the opposite order of values in comparison with catalysts with larger particles ( D > 5–6 nm) – particle size effect.