Oxidative dehydrogenation of isobutane to isobutene III: Reaction mechanism over CePO4 catalyst
Oxidative dehydrogenation of isobutane to isobutene III: Reaction mechanism over CePO4 catalyst
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DOI：
10.1016/j.apcata.2005.07.049
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发表时间：
2005-11
影响因子：
5.5
通讯作者：
Y. Takita;Xia Qing;A. Takami;H. Nishiguchi;Katsutoshi Nagaoka
中科院分区：
文献类型：
--
作者：
Y. Takita;Xia Qing;A. Takami;H. Nishiguchi;Katsutoshi Nagaoka
Among rare earth phosphates, only CePO4and LaPO4exhibit very high activity for oxidative dehydrogenation (ODH) of isobutane. This phenomenon was studied in comparison with the corresponding oxides. Isobutene was formed over NdPO4, which was used as a representative of inactive phosphate catalysts, by simple dehydrogenation with 30–32% selectivity, C3H6and CO2were formed with a selectivity of 25–33% and 20–30%, respectively. Isobutene was obtained at a higher selectivity of 79–86% over CePO4and LaPO4. No H2formation suggests that the essential reaction was the ODH of isobutane. In the oxidation over metal oxides, isobutene selectivity was relatively high: 60–70% over CeO2; however, the essential reaction was considered to be a simple dehydrogenation. Isobutene was formed at 40–47% selectivity, but simple dehydrogenation of isobutane would proceed over Nd2O3and La2O3. La2O3, Nd2O3, and NdPO4have only weak acidic sites. CeO2has weak acidic sites and those with intermediate strength; LaPO4and CePO4have relatively strong acidic sites in addition to the weak acidic sites and those of intermediate strength. Oxidative dehydrogenation activity was correlated with strong acidic sites. ODH of isobutane occurred in the reaction between lattice oxygen of CePO4and isobutane. Introduction of NH3into the reaction system reduced both ODH of isobutane and CO2formation; and stopping the NH3supply led to a resumption of the activity, which suggests the participation of acidic sites. CePO4catalyst contained 2% excess Ce to P; in the prepared CePO4sample, Ce4+was detected by XPS. We conclude that acidic sites and redox between Ce4+and Ce3+play important roles in the ODH of isobutane.
