Selective formation of isobutane and isobutene from synthesis gas over zirconia catalysts

Abstract

Isosynthesis is a process to synthesize isobutane and isobutene from hydrogenation of carbon monoxide. Certain metal oxides such as Z r02 and T h02 are active isosynthesis catalysts. Previous work in the literature concludes that isobutane and isobutene are formed by a series of reactions involving surface intermediates, and these reactions include chain initiation, chain propagation and chain termination. Surface characteristics of the catalyst affects the formation and reaction of the surface intermediates. In this study, isosynthesis was conducted over zirconia based catalysts. The properties of the catalysts were modified by altering synthesis procedure. Basicity was enhanced by preparing the catalysts with the modified sol gel method. Acid-base properties were also modified by adding the oxides of alkali and alkaline metals. Activity tests showed that basic sites on the catalysts surface enhanced the CO insertion, and acidic sites were active in forming methoxide species on the surface. Comparison of different catalysts also revealed that a balanced acid-base property was a key requirement for an active isosynthesis catalyst. In addition to the catalyst work, a kinetic model was developed by modifying the standard polymerization reaction scheme. A step was included in the model to account for the contribution of condensation reaction to the chain growth. Hydrocarbon distributions were calculated from the model, and they agreed reasonably well with the experimental values.