TY - JOUR
T1 - Validation of the Cossee-Arlman mechanism for propylene oligomerization on Ni/UiO-66
AU - Yeh, Benjamin
AU - Chheda, Saumil
AU - Zheng, Jian
AU - Schmid, Julian
AU - Löbbert, Laura
AU - Bermejo-Deval, Ricardo
AU - Gutiérrez, Oliver Y.
AU - Lercher, Johannes A.
AU - Gagliardi, Laura
AU - Bhan, Aditya
N1 - Publisher Copyright:
© 2023 The Royal Society of Chemistry.
PY - 2023/6/21
Y1 - 2023/6/21
N2 - Steady state rate expressions can be derived to distinguish the Cossee-Arlman and metallacycle mechanisms postulated for propylene oligomerization on nickel-based catalysts based on product selectivities, where product selectivities for the former are a function of olefin pressure because sequential coordination and insertion steps lead to independent mechanistic pathways for different hexene isomers. In contrast, the metallacycle mechanism presents pressure-independent product selectivities due to successive coordination prior to the kinetically relevant steps in each mechanism. In this work, steady state propylene oligomerization rates and selectivities were measured in the absence of an activator on nickel functionalized UiO-66 metal organic framework (MOF), Ni/UiO-66, to validate the Cossee-Arlman mechanism for light olefin oligomerization. In situ NO titrations reveal that ∼5% of nickel sites were active during the reaction, and thus, not all nickel sites are relevant for catalysis. Propylene dimerization was first order in propylene pressure from 5 to 500 kPa with an apparent activation energy of ∼20 kJ mol−1 from 453 to 493 K. Calculated apparent activation energies with density functional theory (DFT) calculations on cluster models of Ni/UiO-66 are in agreement with experiment to corroborate the Cossee-Arlman mechanism. Selectivities of hexene products and the ratio of hexene product selectivities on Ni/UiO-66 are in accordance with selectivity expressions derived from the Cossee-Arlman mechanism. Analysis of product selectivities can be used more extensively to demarcate the Cossee-Arlman and metallacycle mechanisms for olefin oligomerization on metal-based catalysts.
AB - Steady state rate expressions can be derived to distinguish the Cossee-Arlman and metallacycle mechanisms postulated for propylene oligomerization on nickel-based catalysts based on product selectivities, where product selectivities for the former are a function of olefin pressure because sequential coordination and insertion steps lead to independent mechanistic pathways for different hexene isomers. In contrast, the metallacycle mechanism presents pressure-independent product selectivities due to successive coordination prior to the kinetically relevant steps in each mechanism. In this work, steady state propylene oligomerization rates and selectivities were measured in the absence of an activator on nickel functionalized UiO-66 metal organic framework (MOF), Ni/UiO-66, to validate the Cossee-Arlman mechanism for light olefin oligomerization. In situ NO titrations reveal that ∼5% of nickel sites were active during the reaction, and thus, not all nickel sites are relevant for catalysis. Propylene dimerization was first order in propylene pressure from 5 to 500 kPa with an apparent activation energy of ∼20 kJ mol−1 from 453 to 493 K. Calculated apparent activation energies with density functional theory (DFT) calculations on cluster models of Ni/UiO-66 are in agreement with experiment to corroborate the Cossee-Arlman mechanism. Selectivities of hexene products and the ratio of hexene product selectivities on Ni/UiO-66 are in accordance with selectivity expressions derived from the Cossee-Arlman mechanism. Analysis of product selectivities can be used more extensively to demarcate the Cossee-Arlman and metallacycle mechanisms for olefin oligomerization on metal-based catalysts.
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U2 - 10.1039/d3cy00570d
DO - 10.1039/d3cy00570d
M3 - Article
AN - SCOPUS:85165216216
SN - 2044-4753
VL - 13
SP - 4213
EP - 4222
JO - Catalysis Science and Technology
JF - Catalysis Science and Technology
IS - 14
ER -