1,2-insertion and 2,1-insertion of comonomer, which was consistent with the
Ti-promotional effect on activity. Moreover, the energy barriers for 2,1-insertion
of comonomer decreased more than those for 1,2-insertion. The calculated results
indicated that 2,1-insertion of comonomer might be enhanced by Ti-modification of
the Phillips catalyst, which was consistent with McDaniel’s suggestion of the
plausible enhancement of the 2,1-insertion versus 1,2-insertion during ethylene
copolymerization with α-olefin on Ti-modified Phillips catalyst [4].
Up to now, most of the theoretical studies on the Phillips catalyst have been
conducted using cluster models built for modeling the active species on the silica
surface. Through a combination of molecular modeling and experimental spectroscopy, a general agreement has been achieved on the cluster model. The reactions
during the induction period, the initiation mechanisms for ethylene polymerization,
and the effects of Ti-modification and fluorination of the silica surface were
elucidated through DFT calculations together with comparison with the experimental results. Because the real Phillips catalyst contains an amorphous silica support
with much higher heterogeneity, the cluster model may neglect the effect of the
silica surface, which is believed to be very important for understanding the active
sites of the Phillips catalyst. Thankfully, with the fast growth in computing power
and the in-depth development of quantum packages, one can perform theoretical
calculations on the Phillips catalyst using a more realistic silica-supported model,
which opens a new era in modeling of the Phillips catalyst. Although the theoretical
calculations using a silica-supported surface model are very limited at present, there
are bright prospects for the realistic molecular modeling of the Phillips catalyst. It is
always crucial to do molecular modeling with a comparison to experiments. The
combination of experiments and theoretical calculations results in more interesting
findings, which probably could not be obtained by means of a single technique. For
the theoretical work in the study of Phillips catalysts, a more realistic mechanistic
description could probably be achieved through a full ab initio quantum molecular
dynamics simulation using a surface-supported model [163]. Believe it or not,
molecular modeling will be playing a more and more important role in the catalytic
field. Theoretical calculation is a powerful tool for interpretation of experimental
results and in guidance of catalyst development through state-of-the-art catalyst
design.
7 Catalyst Innovations Through Modification of the
Phillips Catalyst
Parallel to the progress in the basic understanding on the nature of active sites and
polymerization mechanisms, several modified Phillips catalysts with better performance and improvements in the structures and properties of PE products through
surface modification of the silica support and catalyst with Ti, F, Al, or B
compounds have been successfully developed and commercially applied during
190
R. Cheng et al.
Ti-promotional effect on activity. Moreover, the energy barriers for 2,1-insertion
of comonomer decreased more than those for 1,2-insertion. The calculated results
indicated that 2,1-insertion of comonomer might be enhanced by Ti-modification of
the Phillips catalyst, which was consistent with McDaniel’s suggestion of the
plausible enhancement of the 2,1-insertion versus 1,2-insertion during ethylene
copolymerization with α-olefin on Ti-modified Phillips catalyst [4].
Up to now, most of the theoretical studies on the Phillips catalyst have been
conducted using cluster models built for modeling the active species on the silica
surface. Through a combination of molecular modeling and experimental spectroscopy, a general agreement has been achieved on the cluster model. The reactions
during the induction period, the initiation mechanisms for ethylene polymerization,
and the effects of Ti-modification and fluorination of the silica surface were
elucidated through DFT calculations together with comparison with the experimental results. Because the real Phillips catalyst contains an amorphous silica support
with much higher heterogeneity, the cluster model may neglect the effect of the
silica surface, which is believed to be very important for understanding the active
sites of the Phillips catalyst. Thankfully, with the fast growth in computing power
and the in-depth development of quantum packages, one can perform theoretical
calculations on the Phillips catalyst using a more realistic silica-supported model,
which opens a new era in modeling of the Phillips catalyst. Although the theoretical
calculations using a silica-supported surface model are very limited at present, there
are bright prospects for the realistic molecular modeling of the Phillips catalyst. It is
always crucial to do molecular modeling with a comparison to experiments. The
combination of experiments and theoretical calculations results in more interesting
findings, which probably could not be obtained by means of a single technique. For
the theoretical work in the study of Phillips catalysts, a more realistic mechanistic
description could probably be achieved through a full ab initio quantum molecular
dynamics simulation using a surface-supported model [163]. Believe it or not,
molecular modeling will be playing a more and more important role in the catalytic
field. Theoretical calculation is a powerful tool for interpretation of experimental
results and in guidance of catalyst development through state-of-the-art catalyst
design.
7 Catalyst Innovations Through Modification of the
Phillips Catalyst
Parallel to the progress in the basic understanding on the nature of active sites and
polymerization mechanisms, several modified Phillips catalysts with better performance and improvements in the structures and properties of PE products through
surface modification of the silica support and catalyst with Ti, F, Al, or B
compounds have been successfully developed and commercially applied during
190
R. Cheng et al.