Methods for making a supported chromium catalyst are disclosed, and can comprise contacting a silica-coated alumina containing at least 30 wt. % silica with a chromium-containing compound in a liquid, drying, and calcining in an oxidizing atmosphere at a peak temperature of at least 650 C. to form the supported chromium catalyst. The supported chromium catalyst can contain from 0.01 to 20 wt. % chromium, and typically can have a pore volume from 0.5 to 2 mL/g and a BET surface area from 275 to 550 m.sup.2/g. The supported chromium catalyst subsequently can be used to polymerize olefins to produce, for example, ethylene-based homopolymers and copolymers having high molecular weights and broad molecular weight distributions.

Methods for making a supported chromium catalyst are disclosed, and can comprise contacting a silica-coated alumina containing at least 30 wt. % silica with a chromium-containing compound in a liquid, drying, and calcining in an oxidizing atmosphere at a peak temperature of at least 650 C. to form the supported chromium catalyst. The supported chromium catalyst can contain from 0.01 to 20 wt. % chromium, and typically can have a pore volume from 0.5 to 2 mL/g and a BET surface area from 275 to 550 m.sup.2/g. The supported chromium catalyst subsequently can be used to polymerize olefins to produce, for example, ethylene-based homopolymers and copolymers having high molecular weights and broad molecular weight distributions.

Supported chromium catalysts with an average valence less than +6 and having a hydrocarbon-containing or halogenated hydrocarbon-containing ligand attached to at least one bonding site on the chromium are disclosed, as well as ethylene-based polymers with terminal alkane, aromatic, or halogenated hydrocarbon chain ends. Another ethylene polymer characterized by at least 2 wt. % of the polymer having a molecular weight greater than 1,000,000 g/mol and at least 1.5 wt. % of the polymer having a molecular weight less than 1000 g/mol is provided, as well as an ethylene homopolymer with at least 3.5 methyl short chain branches and less than 0.6 butyl short chain branches per 1000 total carbon atoms.

Catalyst preparation systems and methods for preparing reduced chromium catalysts are disclosed, and can comprise irradiating a supported chromium catalyst containing hexavalent chromium with a light beam having a wavelength within the UV-visible light spectrum. Such reduced chromium catalysts have improved catalytic activity compared to chromium catalysts reduced by other means. The use of the reduced chromium catalyst in polymerization reactor systems and olefin polymerization processes also is disclosed, resulting in polymers with a higher melt index.

The invention relates to a process for transitioning from a first continuous polymerization reaction in a reactor, for example a gas-phase reactor conducted in the presence of a first catalyst to a second continuous polymerization reaction in the reactor conducted in the presence of a second catalyst, wherein the first and second catalysts are incompatible, the process comprising: (a) discontinuing the introduction of the first catalyst from a catalyst feeding system into a reactor and emptying the catalyst feeding system of the first catalyst; (b) introducing a first catalyst killer to the reactor to substantially deactivate the first catalyst in the reactor; (c) introducing a second catalyst killer to the catalyst feeding system to substantially deactivate the first catalyst in the catalyst feeding system; (d) introducing a second catalyst to the catalyst feeding system and (e) introducing the second catalyst to the reactor from the catalyst feeding system, wherein the second catalyst killer is the same as or different from the first catalyst killer.

The invention relates to a process for transitioning from a first continuous polymerization reaction in a reactor, for example a gas-phase reactor conducted in the presence of a first catalyst to a second continuous polymerization reaction in the reactor conducted in the presence of a second catalyst, wherein the first and second catalysts are incompatible, the process comprising: (a) discontinuing the introduction of the first catalyst from a catalyst feeding system into a reactor and emptying the catalyst feeding system of the first catalyst; (b) introducing a first catalyst killer to the reactor to substantially deactivate the first catalyst in the reactor; (c) introducing a second catalyst killer to the catalyst feeding system to substantially deactivate the first catalyst in the catalyst feeding system; (d) introducing a second catalyst to the catalyst feeding system and (e) introducing the second catalyst to the reactor from the catalyst feeding system, wherein the second catalyst killer is the same as or different from the first catalyst killer.

The present invention relates to a ligand compound, a catalyst system for oligomerization of olefins, and a method for oligomerization of olefins using the catalyst system. The catalyst system for oligomerization of olefins according to the present invention not only has excellent catalytic activity, but also exhibits high selectivity to 1-hexene or 1-octene, thus enabling more efficient preparation of alpha-olefin.

The present invention relates to a ligand compound, a catalyst system for oligomerization of olefins, and a method for oligomerization of olefins using the catalyst system. The catalyst system for oligomerization of olefins according to the present invention not only has excellent catalytic activity, but also exhibits high selectivity to 1-hexene or 1-octene, thus enabling more efficient preparation of alpha-olefin.

Supported chromium catalysts with an average valence less than +6 and having a hydrocarbon-containing or halogenated hydrocarbon-containing ligand attached to at least one bonding site on the chromium are disclosed, as well as ethylene-based polymers with terminal alkane, aromatic, or halogenated hydrocarbon chain ends. Another ethylene polymer characterized by at least 2 wt. % of the polymer having a molecular weight greater than 1,000,000 g/mol and at least 1.5 wt. % of the polymer having a molecular weight less than 1000 g/mol is provided, as well as an ethylene homopolymer with at least 3.5 methyl short chain branches and less than 0.6 butyl short chain branches per 1000 total carbon atoms.

Methods for reinforcing chromium catalysts by the deposition of additional silica are disclosed herein. The resultant silica-reinforced chromium supported catalysts can be used to polymerize olefins to produce, for example, ethylene based homopolymers and copolymers with higher molecular weights and additional long chain branching.