Preparation and characterization of Pt/ZnO-Cr2O3 catalyst for low-temperature dehydrogenation of isobutane Original Research Article

Although Pt/ZnO catalyst is effective for low-temperature dehydrogenation of isobutane to isobutene, it is deactivated by the steam added to the reaction system to inhibit coke deposition. Adding Cr, Al, and Ga to ZnO as a third component to the Pt/ZnO catalyst can prevent this deactivation. In this study, the preparation method of ZnO-Cr2O3 and the Cr content in ZnO-Cr2O3 were examined in this context.Pt/ZnO-Cr2O3 catalyst prepared by coprecipitation from homogeneous aqueous nitrates of Zn and Cr with urea exhibited the highest catalytic activity of the catalysts prepared. Isobutane conversion over this catalyst increased with Cr content up to a constant rate at 10 mol%. The characterization of catalysts revealed that Pt/ZnO-Cr2O3 catalyst with large BET surface area and small ZnO crystallite size has high catalytic activity in general. However, it appears that the catalytic activity is affected by the number of free electrons rather than by the BET surface area. In order to generate many free electrons, extensive replacement of Zn with Cr in the ZnO lattice is required, necessitating mixing of Zn and Cr on the atomic scale. This mixing itself results in higher BET surface area and smaller ZnO crystallites. It was also found that most of the Pt surface was covered by carbon, and a small exposed Pt area, which exists in the interface between Pt and ZnO, in where coke was removed by the catalysis of ZnO is the active site for dehydrogenation.