Direct dehydrogenation of isobutane to isobutene over Zn-doped ZrO2 metal oxide heterogeneous catalysts†
A number of excellent reviews have reported that the surface acid–base properties of catalysts play an important role in the dehydrogenation of light alkanes. Moreover, doping of metal oxides can modify their intrinsic properties. Herein, the synthesis of unconventional binary doped oxide heterogeneous catalysts (ZnZrO-x) was described and their respective isobutane dehydrogenation performances were evaluated. The detection results of a range of instrumental analysis techniques revealed that all ZnZrO-x samples comprise nanosized aggregates. CO2/NH3-TPD and Py-IR analyses showed that the incorporation of Zn partially neutralizes inherent strong Lewis acid–base pairs and reduces the surface acidity of ZrO2. XRD, XPS and EPR characterization and activity test results confirmed that coordinatively unsaturated Zr4+ ions (Zrcus4+) near oxygen vacancies (V˙˙O) act as active sites for isobutane dehydrogenation. In addition, the possible reaction pathways and formation of the above active sites were discussed in detail. Among the investigated catalysts, ZnZrO-5 demonstrates the highest dehydrogenation activity and stability, achieving an isobutane conversion of 32.5% with an isobutene selectivity of 94.6% after 7 h time-on-stream.