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<p>The catalytic hydrogenation of phenol was investigated over magnetic Fe<sub>2</sub>O<sub>3</sub>–TiO<sub>2</sub> mixed oxides and a 1 wt.% Rh/Fe<sub>2</sub>O<sub>3</sub>–TiO<sub>2</sub> heterojunction to elucidate the influence of phase composition, textural properties, and metallic promotion on reaction kinetics. Applying a non-linear kinetic approach, bare Fe<sub>2</sub>O<sub>3</sub>–TiO<sub>2</sub> catalysts exhibited significant intrinsic activity associated with the iron oxide phase. Maghemite-rich catalysts (γ-Fe<sub>2</sub>O<sub>3</sub>; S1 and S2) followed pseudo-first&#xa0;order kinetics for phenol conversion, achieving apparent rate constants <i>k</i><sub>1</sub> = 2.10 ± 0.60 and 0.54 ± 0.10&#xa0;h<sup>−1</sup>, and conversions of 47.9 ± 0.9% and 64.9 ± 1.4% correlating positively with the maghemite/hematite ratio. Conversely, the sequential hydrogenation of cyclohexanone to cyclohexanol was mainly controlled by textural features, particularly pore size (10 ± 1–30 ± 3&#xa0;nm) showing higher and well-defined apparent rate constants (<i>k</i><sub><i>2</i></sub> = 1.50–2.90&#xa0;h<sup>−1</sup>) across Fe<sub>2</sub>O<sub>3</sub>-based catalysts. The Rh loading markedly enhanced phenol hydrogenation, achieving near-complete conversion (99.6 ± 1.8%, <i>k</i><sub>1</sub> = 5.76 ± 0.04&#xa0;h<sup>−1</sup>), while successfully arresting the reaction at the partial hydrogenation stage (<i>k</i><sub>2</sub> = 0.42 ± 0.10&#xa0;h<sup>−1</sup>), yielding a high selectivity toward cyclohexanone (77.3 ± 1.4%). Reusability tests over five cycles revealed a progressive decline in phenol conversion (97.4 ± 0.8% to 68.0 ± 1.5%) and cyclohexanone selectivity (81.0 ± 0.7% to 39.6 ± 1.1%) over five cycles. This performance is linked to a significant increase in the sequential rate constant <i>k</i><sub>2</sub> (1.98 ± 0.7 to 6.00 ± 0.62&#xa0;h<sup>−1</sup>), suggesting that surface fouling shifts the process toward over-hydrogenation.</p>

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Phase-dependent kinetics in phenol hydrogenation over magnetic Fe2O3-TiO2 and Rh/Fe2O3-TiO2 catalysts

  • 期刊论文

  • 发表日期：

    2026年2月2日

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  • Jorge Santiago Ferráez-Hernández,
  • Ignacio Cuauhtémoc-López,
  • Luis A. Estudillo-Wong,
  • Adriana Guadalupe Jiménez-Vázquez

摘要

The catalytic hydrogenation of phenol was investigated over magnetic Fe2O3–TiO2 mixed oxides and a 1 wt.% Rh/Fe2O3–TiO2 heterojunction to elucidate the influence of phase composition, textural properties, and metallic promotion on reaction kinetics. Applying a non-linear kinetic approach, bare Fe2O3–TiO2 catalysts exhibited significant intrinsic activity associated with the iron oxide phase. Maghemite-rich catalysts (γ-Fe2O3; S1 and S2) followed pseudo-first order kinetics for phenol conversion, achieving apparent rate constants k1 = 2.10 ± 0.60 and 0.54 ± 0.10 h−1, and conversions of 47.9 ± 0.9% and 64.9 ± 1.4% correlating positively with the maghemite/hematite ratio. Conversely, the sequential hydrogenation of cyclohexanone to cyclohexanol was mainly controlled by textural features, particularly pore size (10 ± 1–30 ± 3 nm) showing higher and well-defined apparent rate constants (k2 = 1.50–2.90 h−1) across Fe2O3-based catalysts. The Rh loading markedly enhanced phenol hydrogenation, achieving near-complete conversion (99.6 ± 1.8%, k1 = 5.76 ± 0.04 h−1), while successfully arresting the reaction at the partial hydrogenation stage (k2 = 0.42 ± 0.10 h−1), yielding a high selectivity toward cyclohexanone (77.3 ± 1.4%). Reusability tests over five cycles revealed a progressive decline in phenol conversion (97.4 ± 0.8% to 68.0 ± 1.5%) and cyclohexanone selectivity (81.0 ± 0.7% to 39.6 ± 1.1%) over five cycles. This performance is linked to a significant increase in the sequential rate constant k2 (1.98 ± 0.7 to 6.00 ± 0.62 h−1), suggesting that surface fouling shifts the process toward over-hydrogenation.