A spectroscopic investigation of isopropanol and methylbutynol as infrared reactive probes for base sites on polycrystalline metal oxide surfaces

Self-supporting wafers of silica, alumina, titania and zirconia were exposed to gas phase molecules of isopropanol or methylbutynol at different temperatures (up to 400degreesC) in situ a specially designed infrared (IR) reactor/cell. Following cooling to room temperature, IR spectra were taken of the gas phase and the wafer, which were subsequently handled automatically to obtain difference spectra of the gas phase and adsorbed products of the alcohol interactions with the oxide surface. The results were discussed for a thorough assessment of the reliability of the application of each of the two alcohols as an IR reactive probe for base sites exposed on the oxide surfaces. The prominent conclusions drawn from the present investigation are the following: (i) adsorptive and catalytic interactions of methylbutynol are more specific to the surface base sites than those of isopropanol, (ii) primary and secondary (further) adsorptive interactions of the alcohol and its decomposition products are more informative than the catalytic interactions, (iii) non-dissociative adsorptive interactions are a better probe of the surface base sites than dissociative ones, and (iv) silica surfaces have no detectable base sites, whereas the other test oxides do have base sites and reveal the following increasing order of basicity: Al < Zr < Ti. (C) 2002 Elsevier Science B.V. All rights reserved.