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

Abstract

The dehydrogenation of isobutane to isobutene was accomplished using a NiO/γ-Al 2 O 3 catalyst. Furthermore, signi cant 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 signi cantly 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-Al 2 O 3 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-Al 2 O 3 catalyst with small and large NiO loadings led to similar results to those of isobutane dehydrogenation. In addition, it was con rmed 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-Al 2 O 3 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.

エタン，プロパンおよびイソブタンの脱水素により析出した大量の炭素に覆われたアルミナ担持酸化ニッケルの触媒再生

“…However, as expected from Scheme 1, the catalyst was clearly regenerated by the oxygen treatment, with catalytic activity improving with time-on-stream. In all runs, the selectivity to ethylene increased with time-on-stream, which indicates that formation of highly dispersed Ni on the fibrous carbon proceeded with time-on-stream as reported in our previous study 5) . The catalytic activity was not completely regenerated after oxygen treatment, which indicates the contribution of new chemical species other than Ni, NiO, γ-Al2O3, or carbon.…”

“…In particular, nickel-based catalysts are rarely used in catalytic dehydrogenation because of the formation of significant carbon deposits 3),4) . In contrast, our recent studies on the catalytic dehydrogenations of ethane 5) , propane 5) , and isobutane 6),7) on γ-alumina-supported nickel oxides (NiO/ γ-Al2O3) have shown dramatic improvements in the yield of the corresponding dehydrogenated products with time-on-stream. We credit this improvement to the formation of highly dispersed metallic nickel on the carbon nanotube-like deposits.…”

“…By changing the partial pressure of ethane in the feedstream, in Run 1 of Fig. 1, the yield of ethylene yield was maximized at 3.25 h on-stream, although the yield continued to increase up to 6 h on-stream at partial pressure of ethane of 14.1 kPa 5) . Between Runs 1 and 5, each catalyst was treated with oxygen diluted with helium (total flow rate＝30.7 mL/min and the partial pressure of oxygen＝66 kPa) for 2 h at 823 K. The oxygen treatment conditions were optimized to completely remove carbon deposits from the catalyst recovered in Run 1 and to convert the metallic nickel formed during Run 1 to nickel oxide.…”

“…Dehydrogenation of ethane produces ethylene and methane. Regeneration of deactivated catalyst via oxygen treatment was examined under the partial pressure of 29.0 kPa ethane, increased from the standard condition of 14.1 kPa 5) under the reaction conditions of Run 1 shown in Fig. 1.…”

“…2. Other reaction conditions were the same as previously reported 5) , and Runs 2 to 3 used the same conditions as Run 1. By changing the partial pressure of propane in the feedstream as above, in Run 1 of Fig.…”