TY - JOUR

T1 - The effect of ruthenium promotion of the Co/δ-Al2O3 catalyst on the hydrogen reduction kinetics of cobalt

AU - Kungurova, Olga A.

AU - Shtertser, Natalya V.

AU - Koemets, Egor G.

AU - Cherepanova, Svetlana V.

AU - Khassin, Alexander A.

N1 - Publisher Copyright: © 2016, Akadémiai Kiadó, Budapest, Hungary.

PY - 2017/4/1

Y1 - 2017/4/1

N2 - The effect of ruthenium content on the reductive activation of the Co/δ-Al2O3 catalyst was investigated using thermal analysis and in situ synchrotron radiation X-ray diffraction. Data of thermal analysis and phase transformations can be described by a kinetic scheme consisting of three sequential steps: Co3+ → Co2+ → (Co0Co2+) → Co0. The first step is the generation of several CoO clusters within one Co3O4 crystallite followed by their further growth obeying the Avrami–Erofeev kinetic equation (An1) with dimensional parameter n1 < 1, which may indicate the diffusion control of the growth. The second step is the kinetically controlled sequential process of the metallic cobalt phase nucleation (An2), which is followed by the third step of slow particle growth limited by mass transport according to the Jander model (D). Ruthenium promotion of Co/δ-Al2O3 catalysts significantly accelerates the reduction of cobalt. As the ruthenium content is raised to 1 wt%, the characteristic temperature of metal phase formation decreases by more than 200 °C and Ea for An2 step decreases by 25%. For step D, a joint decrease in activation energy and pre-exponential factor in case of ruthenium promotion corresponds to a weaker diffusion impediment at the final step of cobalt reduction. In the case of unmodified Co/δ-Al2O3, the characteristic temperature of the metal phase formation reaches very high values, the metallic nuclei rapidly coalesce into larger ones, and the further process is inhibited by diffusion of the reactants through the product layer. For ruthenium promoted catalysts, each CoO crystallite generates one metal crystallite; thus, ruthenium enhances the dispersion of the active component.

AB - The effect of ruthenium content on the reductive activation of the Co/δ-Al2O3 catalyst was investigated using thermal analysis and in situ synchrotron radiation X-ray diffraction. Data of thermal analysis and phase transformations can be described by a kinetic scheme consisting of three sequential steps: Co3+ → Co2+ → (Co0Co2+) → Co0. The first step is the generation of several CoO clusters within one Co3O4 crystallite followed by their further growth obeying the Avrami–Erofeev kinetic equation (An1) with dimensional parameter n1 < 1, which may indicate the diffusion control of the growth. The second step is the kinetically controlled sequential process of the metallic cobalt phase nucleation (An2), which is followed by the third step of slow particle growth limited by mass transport according to the Jander model (D). Ruthenium promotion of Co/δ-Al2O3 catalysts significantly accelerates the reduction of cobalt. As the ruthenium content is raised to 1 wt%, the characteristic temperature of metal phase formation decreases by more than 200 °C and Ea for An2 step decreases by 25%. For step D, a joint decrease in activation energy and pre-exponential factor in case of ruthenium promotion corresponds to a weaker diffusion impediment at the final step of cobalt reduction. In the case of unmodified Co/δ-Al2O3, the characteristic temperature of the metal phase formation reaches very high values, the metallic nuclei rapidly coalesce into larger ones, and the further process is inhibited by diffusion of the reactants through the product layer. For ruthenium promoted catalysts, each CoO crystallite generates one metal crystallite; thus, ruthenium enhances the dispersion of the active component.

KW - Cobalt–alumina catalysts

KW - Kinetics

KW - Mechanism

KW - Promotion

KW - Reduction

KW - Ruthenium

KW - OXIDE

KW - PLATINUM

KW - STATE

KW - PARAMETERS

KW - CO

KW - REDUCIBILITY

KW - SUPPORT

KW - CO3O4

KW - FISCHER-TROPSCH SYNTHESIS

KW - Cobalt-alumina catalysts

UR - http://www.scopus.com/inward/record.url?scp=85006355078&partnerID=8YFLogxK

U2 - 10.1007/s11144-016-1118-2

DO - 10.1007/s11144-016-1118-2

M3 - Article

AN - SCOPUS:85006355078

VL - 120

SP - 501

EP - 525

JO - Reaction Kinetics, Mechanisms and Catalysis

JF - Reaction Kinetics, Mechanisms and Catalysis

SN - 1878-5190

IS - 2

ER -