Abstract Isomerization of α-pinene epoxide was carried out over a Colombian natural zeolite as potential geocatalyst with heulandite, chabazite and clipnotilolite as main crystallographic phases; the heulandite was identified as the active phase. Over synthetic zeolites, isomerization of α-pinene epoxide depended on Si/Al ratio, unit cell and the kind of structure. The best solvent was toluene and not isomerization activity was observed in presence of solvents with carboxyl groups. Complete α-pinene epoxide conversion and 45% selectivity to campholenic aldehyde were obtained at 70 °C, with fencholenic aldehyde, carveol, and p -cymene as main by-products. Decrease of activity of natural zeolite was associated with loss of acid sites. A reaction mechanism based on experimental and computational data was proposed including adsorption of α-pinene epoxide on Fe or Al sites of the natural zeolite; a reaction rate constant of 4.02 × 10 –4 mol g −1 min −1 was estimated from a pseudo homogeneous kinetic model. Graphic Abstract

中文翻译：

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α-蒎烯环氧化物在天然沸石上的催化异构化

摘要 α-蒎烯环氧化物的异构化反应以哥伦比亚天然沸石为潜在的地质催化剂，以片沸石、菱沸石和菱沸石为主要晶相；片沸石被确定为活性相。在合成沸石上，α-蒎烯环氧化物的异构化取决于硅铝比、晶胞和结构类型。最好的溶剂是甲苯，在有羧基的溶剂存在下没有观察到异构化活性。在 70 °C 下，α-蒎烯环氧化物完全转化，对樟脑醛的选择性为 45%，主要副产物为苯酚醛、香芹醇和对伞花烃。天然沸石活性的降低与酸性位点的损失有关。提出了基于实验和计算数据的反应机理，包括将α-蒎烯环氧化物吸附在天然沸石的 Fe 或 Al 位点上；从拟均相动力学模型估计反应速率常数为 4.02 × 10 –4 mol g -1 min -1。图形摘要