Enhancement of the Catalytic Activity Associated with Carbon Deposition Formed on NiO/Al₂O₃ during the Dehydrogenation of Ethane and Propane

抄録

The dehydrogenation of isobutane to isobutene was accomplished using a NiO/γ-Al₂O₃ catalyst. Furthermore, significant improvement in the time-on-stream yield of isobutene was achieved. During the normal catalytic dehydrogenation of alkanes, the catalyst is covered by carbon deposition generated during the reaction, which significantly reduces the activity with time-on-stream. Therefore, no examples of the catalytic dehydrogenation of isobutane have yet been reported. This study used either ethane or propane as a source of isobutane to examine whether the activity was improved with time-on-stream. As a result, in the dehydrogenations of both ethane and propane on a NiO/γ-Al₂O₃ catalyst, the catalytic activity decreased with time-on-stream when the supporting amount of NiO was small. In contrast, when the supporting amount of NiO was large, the catalytic activity improved with time-on-stream. Using a NiO/γ-Al₂O₃ catalyst with small and large NiO loadings led to similar results to those of isobutane dehydrogenation. In addition, it was confirmed that the dehydrogenation activity was improved with time-on-stream in the catalytic dehydrogenations of ethane, propane, and isobutane using high NiO loadings. The behavior using a moderate amount of NiO loading, which was not detected in the dehydrogenation of isobutane, was also observed, which resulted in a maximum yield of either ethylene or propylene at 2.0 or 3.25 h on-stream, respectively. We concluded that the reason the catalytic activity did not improve with time-on-stream when using a NiO/γ-Al₂O₃ catalyst was because the supporting amount of NiO was negligible. These results demonstrate that the activity with time-on-stream could also be improved in the dehydrogenations of other alkanes.