Catalysis Engineering, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands.
Phys Chem Chem Phys. 2011 Jan 28;13(4):1345-55. doi: 10.1039/c0cp00879f. Epub 2010 Dec 14.
The rate of cyclohexane photo-catalytic oxidation to cyclohexanone over anatase TiO(2) was studied at temperatures between 23 and 60 °C by in situ ATR-FTIR spectroscopy, and the kinetic parameters were estimated using a microkinetic model. At low temperatures, surface cyclohexanone formation is limited by cyclohexane adsorption due to unfavorable desorption of H(2)O, rather than previously proposed slow desorption of the product cyclohexanone. Up to 50 °C, the activation energy for photocatalytic cyclohexanone formation is zero, while carboxylates are formed with an activation energy of 18.4 ± 3.3 kJ mol(-1). Above 50 °C, significant (thermal) oxidation of cyclohexanone contributes to carboxylate formation. The irreversibly adsorbed carboxylates lead to deactivation of the catalyst, and are most likely the predominant cause of the non-Arrhenius behavior at relatively high reaction temperatures, rather than cyclohexane adsorption limitations. The results imply that elevating the reaction temperature of photocatalytic cyclohexane oxidation reduces selectivity, and is not a means to suppress catalyst deactivation.
在 23 至 60°C 的温度范围内，通过原位 ATR-FTIR 光谱法研究了环己烷在锐钛矿 TiO(2)上光催化氧化为环己酮的速率，并使用微观动力学模型估算了动力学参数。在低温下，由于 H(2)O 不利的脱附，表面环己酮的形成受到环己烷吸附的限制，而不是先前提出的产物环己酮的缓慢脱附。在 50°C 以下，光催化环己酮形成的活化能为零，而羧酸根的形成具有 18.4±3.3 kJ mol(-1)的活化能。在 50°C 以上，环己酮的显著（热）氧化对羧酸根的形成有贡献。不可逆吸附的羧酸根导致催化剂失活，它们很可能是在相对较高的反应温度下出现非 Arrhenius 行为的主要原因，而不是环己烷吸附限制。结果表明，提高光催化环己烷氧化的反应温度会降低选择性，并不是抑制催化剂失活的手段。
