In situ UV–Vis diffuse reflectance spectroscopy — on line activity measurements of supported chromium oxide catalysts: relating isobutane dehydrogenation activity with Cr-speciation via experimental design

The dehydrogenation of isobutane over supported chromium oxide catalysts was studied by a combination of in situ UV–Vis diffuse reflectance spectroscopy and on line GC analysis. A well-defined set of experiments, based on an experimental design, was carried out to develop mathematical models, which quantitatively relate Cr-speciation and dehydrogenation activity with reaction temperature and time, support composition, gas composition and Cr loading. It will be shown that: (1) the dehydrogenation activity is proportional with the amount of in situ measured surface Cr2qr3q, and maximum for a 7.5 wt.% CrrAl2O3 catalyst operating at 5008C in 2% isobutane in N2; and (2) Cr 3q-sites are more active in alkane dehydrogenation than Cr2q-sites. This paper is the first example of the use of experimental design for deriving structure–activity relationships in the field of heterogeneous catalysis