TY - JOUR
T1 - Characterization of nickel catalysts with transient methods
AU - Ewald, Stefan
AU - Standl, Sebastian
AU - Hinrichsen, Olaf
N1 - Publisher Copyright:
© 2017 Elsevier B.V.
PY - 2018
Y1 - 2018
N2 - The Ni surface area is a key factor in catalytic performance of supported Ni catalysts employed in heterogeneously catalyzed reactions. For its characterization, transient measurement techniques are powerful but need a proper experimental design and a high level of accuracy. In this study, several transient methods, namely temperature programmed desorption of H2 (H2-TPD), pulsed H2 chemisorption and N2O chemisorption, were applied and evaluated for the characterization of Ni catalysts. Results were compared with those from static H2 chemisorption. Ni powder, as well as NiAlOx and Ni/γ-Al2O3 with varying Ni loadings, synthesized via precipitation and incipient wetness impregnation, respectively, were used as model catalysts. H2-TPD within the temperature range from 84 to 753 K is able to completely describe the interaction of H2 with supported Ni. However, a quantitative analysis of the specific Ni surface area based on H2-TPD is difficult whereas pulsed H2 chemisorption leads to comparable results as obtained from static measurements. Adsorption and pre-treatment conditions have a strong impact on the desorption spectra. Reversible morphologic changes of the Ni surface were revealed by H2-TPD when changing the gas atmosphere during pre‐treatment. N2O chemisorption occurs in three steps including fast oxygen uptake, growth of the oxide layer and subsequent layer thickening due to subsurface and bulk oxidation. A separation of surface and subsurface/bulk oxidation of NiAlOx and Ni/γ-Al2O3, both of which are readily oxidized even under mild conditions, is only achievable at temperatures between 190 and 195 K. In this temperature range, the ratio of adsorbed oxygen atoms, O, and the number of Ni surface atoms, NiS, (O/NiS) is 0.38 ± 0.07, which can be applied for specific Ni surface area determination. The experimental mode of N2O chemisorption (flow or titration mode) does not influence the extent of subsurface oxidation. The separation of surface and subsurface/bulk oxidation is more feasible in the case of Ni powder. Here, a suitable temperature for Ni surface area determination lies within 265 and 285 K with an O/NiS ratio of 0.96 ± 0.05.
AB - The Ni surface area is a key factor in catalytic performance of supported Ni catalysts employed in heterogeneously catalyzed reactions. For its characterization, transient measurement techniques are powerful but need a proper experimental design and a high level of accuracy. In this study, several transient methods, namely temperature programmed desorption of H2 (H2-TPD), pulsed H2 chemisorption and N2O chemisorption, were applied and evaluated for the characterization of Ni catalysts. Results were compared with those from static H2 chemisorption. Ni powder, as well as NiAlOx and Ni/γ-Al2O3 with varying Ni loadings, synthesized via precipitation and incipient wetness impregnation, respectively, were used as model catalysts. H2-TPD within the temperature range from 84 to 753 K is able to completely describe the interaction of H2 with supported Ni. However, a quantitative analysis of the specific Ni surface area based on H2-TPD is difficult whereas pulsed H2 chemisorption leads to comparable results as obtained from static measurements. Adsorption and pre-treatment conditions have a strong impact on the desorption spectra. Reversible morphologic changes of the Ni surface were revealed by H2-TPD when changing the gas atmosphere during pre‐treatment. N2O chemisorption occurs in three steps including fast oxygen uptake, growth of the oxide layer and subsequent layer thickening due to subsurface and bulk oxidation. A separation of surface and subsurface/bulk oxidation of NiAlOx and Ni/γ-Al2O3, both of which are readily oxidized even under mild conditions, is only achievable at temperatures between 190 and 195 K. In this temperature range, the ratio of adsorbed oxygen atoms, O, and the number of Ni surface atoms, NiS, (O/NiS) is 0.38 ± 0.07, which can be applied for specific Ni surface area determination. The experimental mode of N2O chemisorption (flow or titration mode) does not influence the extent of subsurface oxidation. The separation of surface and subsurface/bulk oxidation is more feasible in the case of Ni powder. Here, a suitable temperature for Ni surface area determination lies within 265 and 285 K with an O/NiS ratio of 0.96 ± 0.05.
KW - Determination of Ni surface sites
KW - NO chemisorption
KW - Ni catalyst
KW - Pulsed chemisorption of H
KW - Temperature programmed desorption of H
UR - http://www.scopus.com/inward/record.url?scp=85030148601&partnerID=8YFLogxK
U2 - 10.1016/j.apcata.2017.09.023
DO - 10.1016/j.apcata.2017.09.023
M3 - Article
AN - SCOPUS:85030148601
SN - 0926-860X
VL - 549
SP - 93
EP - 101
JO - Applied Catalysis A: General
JF - Applied Catalysis A: General
ER -