Catalytic performance of zirconia and mixed oxide zirconia catalysts in isobutene synthesis from synthesis gas

Abstract

The catalytic performances of various zirconia, ceria and zirconia-ceria mixed oxide catalysts on isosynthesis were studied. The characteristics of the catalysts were determined by using various techniques including BET surface area, XRD, NH[subscript 3-] and CO[subscript 2]-TPD, and SEM/EDX. For micron- and nanoscale zirconia and ceria catalysts, it was found that nanoscale catalysts showed higher activity and selectivity of isobutene in hydrocarbons than micronscale ones. The acid-base properties and phase composition of zirconia influenced the catalytic performance. Effect of temperature ramp during calcination was also investigated. Lower heating rate of calcination exhibited an increase in monoclinic phase in zirconia. The studies revealed that higher selectivity of isobutene in hydrocarbons was resulted from higher intensity of Zr[superscript 3+] and/or more fraction of tetragonal phase present. The catalytic performances of zirconia-ceria mixedoxide catalysts prepared by coprecipitation and physical mixing method were studied. The major factor determining the activity and selectivity of isobutene was the amount of Zr[superscript 3+]. Intensity of Zr[superscript 3+] decreased when ceria was added to zirconia for both preparation methods. It was observed that the physical mixing method exhibited better selectivity of isobutene in hydrocarbons than coprecipitation method in lower content of ceria of 69.2%. It revealed that quantity of Zr[superscript 3+] in the former method was higher than that of the latter. Therefore, it was concluded that the difference in the quantity of Zr[superscript 3+] influenced the catalytic performance of the catalysts. Furthermore, the suitable reaction temperature for isosynthesis was 400 ํC.