Abstract:
The focus of this research was to investigate the catalytic performances of various zirconia catalysts on isosynthesis. The characteristics of the catalysts were determined by means of various techniques including BET surface area, XRD, NH[[subscript 3][superscript -]] and CO[[subscript 2][superscript -]] TPD, TEM and SEM/EDX. In the first portion, different micron- and nanoscale zirconia catalysts were employed for the isosynthesis and compared with those of ceria. It was found that the nanoscale catalysts showed higher activity and selectivity of isobutene in hydrocarbons than the micronscales ones. Based on the nanoscales catalysts, ceria exhibited the highest activity among other zirconia catalysts, but lower selectivity for isobutene. In fact, the acid-base properties and phase composition of zirconia apparently influenced the catalytic performance. In the second portion, effect of temperature ramp during calcination of zirconia on characteristics of nanoscale zirconia catalysts and their catalytic performance for isosynthesis was investigated. It was found that increased temperature ramp rate of calcination resulted in higher composition of tetragonal phase. Considering the catalytic activity, the acid sites did not affect activity, but the basic sites did which depended on the fraction of tetragonal phase in zirconia which was related to selectivity of isobutene. In particular, the intensity of Zr [superscript 3+] on the surface obtained from the electron spin resonance spectroscopy (ESR) varied with the change in the heating rate of calcination. The indicated that the composition of tetragonal phase and Zr [superscript 3+] were the key factors that can affect the selectivity of isobutene during isosynthesis.
