the past 60 years [2–4, 11]. It is obvious that the catalyst innovations are very
limited. During the past few years, we have successfully developed several novel
Cr-based Phillips-type catalysts through simple surface modifications of the traditional Phillips catalyst, as shown in Scheme 20. Two basic procedures were taken
into consideration for the innovations. One procedure was modification of surface
chromate species using various types of organic silanols (to give Cat-A and Cat-B).
The other procedure was modification of surface residual hydroxyl groups using
various types of organometallic compounds, which could be chemically anchored
on the catalyst surface and provide extra active sites for ethylene polymerization
(giving Cat-C).
7.1 Modification of Surface Chromate Species on the Phillips
Catalyst
Modification of surface chromate species on the Phillips catalyst using various
types of organic silanols could be a general procedure for synthesis of various novel
Cr-based polymerization catalysts. The reactions are shown in Scheme 20 for Cat-A
and Cat-B. The first example of Cat-A was reported by Cann and coworkers
through the reaction between TPS and a Phillips catalyst with the original purpose
of transformation of the Phillips catalyst into UCC S-2 catalyst in order to avoid the
use of toxic and expensive BC [27]. In our opinion, the Cat-A was similar to the
UCC S-2 catalyst but differed with respect to the simultaneously formed surface
Scheme 20 Procedures for preparation of novel catalysts (Cat-A, Cat-B and Cat-C) by modification of the Phillips catalyst
Phillips Cr/Silica Catalyst for Ethylene Polymerization
191
limited. During the past few years, we have successfully developed several novel
Cr-based Phillips-type catalysts through simple surface modifications of the traditional Phillips catalyst, as shown in Scheme 20. Two basic procedures were taken
into consideration for the innovations. One procedure was modification of surface
chromate species using various types of organic silanols (to give Cat-A and Cat-B).
The other procedure was modification of surface residual hydroxyl groups using
various types of organometallic compounds, which could be chemically anchored
on the catalyst surface and provide extra active sites for ethylene polymerization
(giving Cat-C).
7.1 Modification of Surface Chromate Species on the Phillips
Catalyst
Modification of surface chromate species on the Phillips catalyst using various
types of organic silanols could be a general procedure for synthesis of various novel
Cr-based polymerization catalysts. The reactions are shown in Scheme 20 for Cat-A
and Cat-B. The first example of Cat-A was reported by Cann and coworkers
through the reaction between TPS and a Phillips catalyst with the original purpose
of transformation of the Phillips catalyst into UCC S-2 catalyst in order to avoid the
use of toxic and expensive BC [27]. In our opinion, the Cat-A was similar to the
UCC S-2 catalyst but differed with respect to the simultaneously formed surface
Scheme 20 Procedures for preparation of novel catalysts (Cat-A, Cat-B and Cat-C) by modification of the Phillips catalyst
Phillips Cr/Silica Catalyst for Ethylene Polymerization
191