Brønsted-type relationship for surface active sites on solid acid catalysts: 1-butene isomerization on TiO2SiO2, ZrO2SiO2, and Al2O3SiO2 mixed oxide catalysts

Acidic properties (acid sites' strength and concentration) of three series of mixed oxide catalysts (titania-silica, zirconia-silica and alumina-silica) were analyzed by proton affinity distributions. Catalytic properties under mild dehydration conditions (1-butene isomerization at 423 K) of these materials were also evaluated. A Brønsted-type correlation was found between first-order apparent isomerization rate constants and acid strengths of certain components of the pK spectra of the catalysts. This was explained in terms of proton transfer processes that take place at both wet and dry interfaces, i.e. at the surface hydroxyl layer. The results were discussed in terms of Fourier transform infrared data which indicate the presence of large surface hydroxyl populations on all catalysts under the reaction conditions.