Abstract:

The relationship between the high selectivity of catalysis and the structure of active centre of copper colloidal catalyst in selective hydration of acrylonitrile to acrylamide was studied. Colloidal copper particles were prepared by reducing copper(Ⅱ) chloride solution with the mixed solution of hydrazine hydrate and sodium hydroxide in the presence of stabilizer polyvinyl pyrrolidone(PVP). The copper colloids stabilized by PVP were used as the catalyst in selective hydration of acrylonitrile to acrylamide with a selectivity of 100%. Therefore, the character of colloidal copper catalyst is its high selectivity. According to the properties of defects on the surface of colloidal copper particles, the reasons of the high selectivity are analyzed: (1) The type of the active centre is singled. According to the theories of defect and experimental results, it is shown that the active centre of metal copper is not point defect, but the end point of dislocation. (2) The structure of the active centre is stable. The experimental results show that the colloidal copper particle have mechanical properties of high hardness and high strength, which keep the structure of active centre stability. Meanwhile, the size of the colloidal particles is 45 nm longer than that of particles, dislocation of which can exist stably. So the dislocation can exist stably on the colloidal copper particles. This further ensures the stability of the structure active centre. We also propose the view point that a proper size space is needed for active centre existing stably on the surface of the catalyst. This explains the reason that colloidal catalyst particles under a certain size will lose its catalytic activity.

Key words: Colloidal copper; Catalyst; High selectivity; Acrylonitrile