Controlled deposition of chromium hexacarbonyl on silica surfaces in a fluidised bed reactor

Cr(CO)(6)/silica samples were prepared in a fluidised bed reactor by vapor phase adsorption of zerovalent chromium hexacarbonyl under N-2 flow. Two di fferent preparation methods were used; a vaporisation method without decarb onylation step and a pulse method in which a sample was decarbonylated afte r vaporisation, followed by repeated vaporisation-decarbonylation cycles. T he chromium content can be controlled and weakly adsorbed chromium species can also be removed from the silica surface using the pulse method. The chr omium carbonyl/silica interactions were characterised using diffuse reflect ance Fourier transform IR spectroscopy (DRIFT). Si-29 cross-polarisation ma gic-angle spinning (CP MAS) NMR studies indicated that chromium hexacarbony l interacts with single silanols of the silica surface even though the inte raction is either physisorption or weak chemisorption. Samples were also ch aracterised by temperature programmed techniques. The preoxidation temperat ure influences to the reduction of the samples. (C) 2000 Elsevier Science B .V. All rights reserved.