Structure of the catalytic site on a silica-supported catalyst derived from copper(II) acetate

Abstract

The structure of the copper site on a silica-supported catalyst derived from copper(II) acetate has been determined by means of XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) in comparison with that derived from tetra-ammine copper(II). The former catalyst has a highly dispersed binuclear structure, which is similar to that observed in copper(II) acetate monohydrate. The catalyst calcined in an O₂ atmosphere at 300 °C forms a chain composed of CuO parallelogram units. A low-dimensional metallic copper cluster develops on the catalyst reduced by CO at 300 °C. The catalyst derived from tetraammine copper(II) contains highly dispersed mononuclear units in the fresh state. A three-dimensional imperfect microcluster of CuO disperses on the calcined sample and changes to a highly dispersed monovalent mononuclear species on reduction with CO at 300 °C. The low-dimensional structure with strong metal–metal interaction should be the cause of high catalytic activity in the acetate catalyst, whereas the lack of metal–metal order and hindrance of active sites by the three-dimensional structure decreases the catalytic activity of the tetra-ammine catalyst.