Increasing the availability of active sites in Zn-Co double metal cyanides by dispersion onto a SiO2 support

Abstract

Zn-Co double metal cyanides (DMCs) were dispersed on silica by dry and liquid-assisted (LAG) grinding to improve the catalytic performance of the DMC phase. The characterization of the resulting materials by transmission electron microscopy, N2 physisorption, and powder X-ray diffraction indicated that the presence of water during the grinding step, not only helped to preserve the structural and textural properties of the DMC, but also facilitated the dispersion of the active phase onto the silica support. The accessibility of the Lewis acid sites was increased, as evidenced by FTIR spectroscopy with pyridine as probe molecule. The catalytic activity of the DMC phase for both the hydroamination of phenylacetylene with 4-isopropylaniline and the ring opening polymerization of 1,2-epoxyhexane was enhanced upon dispersion on silica due to the greater availability of the active Zn(II) sites. As a result, higher turnover frequencies were obtained upon decreasing the amount of DMC in the sample. The positive effect on the catalytic activity was the most pronounced for the catalysts prepared via LAG.