TY - JOUR
T1 - Surface Investigation and Morphological Analysis of Structurally
Disordered MgCl2 and MgCl2/TiCl4 Ziegler-Natta Catalysts
AU - D'AMORE, MADDALENA
AU - Thushara, K. S.
AU - Alessandro, Piovano
AU - Mauro, Causa
AU - Bordiga, Silvia
AU - Elena, Groppo
PY - 2016
Y1 - 2016
N2 - Activated MgCl2 nanocrystals were prepared by controlled dealcoholation
of the MgCl2 center dot 6CH(3)OH adduct, mimicking the routinely adopted
methods to synthesize industrial heterogeneous Ziegler Natta catalysts.
The effect of the alcohol in driving the morphology of MgCl2 crystals,
i.e., the type and extension of the exposed surfaces, was investigated
by integrating a detailed structural, morphological, and surface
characterization with a state-of-the-art computational modeling. FT-IR
spectroscopy of CO adsorbed at 100 K emerged as a feasible, simple, and
powerful method to characterize the surface of structurally disordered
MgCl2 and MgCl2-based Ziegler Natta catalysts. Our computational
morphological analysis revealed that the (012), (015), and (110)
surfaces are highly stabilized donor, especially at the temperature
typically adopted in the preparation of the precatalysts. FT-IR
spectroscopy of adsorbed CO allows distinguishing these surfaces from
the other penta-coordinated ones and provides a clear experimental
evidence that TiCl4 binds to the (110) and (015) surfaces. The (015)
surface was never considered in the past and is characterized by an
unusual flexibility in the presence of adsorbates, which detach the Mg
cations from the Cl underneath, leaving a coordination vacancy available
for the binding of asymmetric titanium sites. Since the recent
literature identified a tetra-coordinated Mg as a site of election for
the deposition of the Ti species relevant in olefin polymerization, the
presence of two eligible Mg sites for Ziegler Natta catalysis is highly
interesting.
AB - Activated MgCl2 nanocrystals were prepared by controlled dealcoholation
of the MgCl2 center dot 6CH(3)OH adduct, mimicking the routinely adopted
methods to synthesize industrial heterogeneous Ziegler Natta catalysts.
The effect of the alcohol in driving the morphology of MgCl2 crystals,
i.e., the type and extension of the exposed surfaces, was investigated
by integrating a detailed structural, morphological, and surface
characterization with a state-of-the-art computational modeling. FT-IR
spectroscopy of CO adsorbed at 100 K emerged as a feasible, simple, and
powerful method to characterize the surface of structurally disordered
MgCl2 and MgCl2-based Ziegler Natta catalysts. Our computational
morphological analysis revealed that the (012), (015), and (110)
surfaces are highly stabilized donor, especially at the temperature
typically adopted in the preparation of the precatalysts. FT-IR
spectroscopy of adsorbed CO allows distinguishing these surfaces from
the other penta-coordinated ones and provides a clear experimental
evidence that TiCl4 binds to the (110) and (015) surfaces. The (015)
surface was never considered in the past and is characterized by an
unusual flexibility in the presence of adsorbates, which detach the Mg
cations from the Cl underneath, leaving a coordination vacancy available
for the binding of asymmetric titanium sites. Since the recent
literature identified a tetra-coordinated Mg as a site of election for
the deposition of the Ti species relevant in olefin polymerization, the
presence of two eligible Mg sites for Ziegler Natta catalysis is highly
interesting.
UR - https://iris.uniupo.it/handle/11579/198042
U2 - 10.1021/acscatal.6b00871
DO - 10.1021/acscatal.6b00871
M3 - Article
SN - 2155-5435
VL - 6
SP - 5786
EP - 5796
JO - ACS Catalysis
JF - ACS Catalysis
IS - 9
ER -