Editing Ziegler–Natta catalyst (section)

===Heterogeneous catalysts===
{{main|Heterogeneous catalysis}}
The first and dominant class of titanium-based catalysts (and some [[vanadium]]-based catalysts) for alkene polymerization can be roughly subdivided into two subclasses:
* catalysts suitable for homopolymerization of ethylene and for ethylene/1-alkene [[copolymer]]ization reactions leading to copolymers with a low 1-alkene content, 2–4&nbsp;mol% ([[LLDPE]] resins), and
* catalysts suitable for the synthesis of isotactic 1-alkenes.
The overlap between these two subclasses is relatively small because the requirements to the respective catalysts differ widely.

Commercial catalysts are supported by being bound to a solid with a high surface area. Both [[titanium tetrachloride|TiCl<sub>4</sub>]] and [[titanium trichloride|TiCl<sub>3</sub>]] give active catalysts.<ref name="ref1">{{cite book|last=Hill|first= A. F. |title=Organotransition Metal Chemistry |publisher=Wiley-InterScience|location= New York|date= 2002| pages= 136–139}}</ref><ref name="ref2">{{cite book|last=Kissin|first= Y. V. |title=Alkene Polymerization Reactions with Transition Metal Catalysts |publisher=Elsevier|location= Amsterdam|date= 2008 |chapter=Chapter 4}}</ref> The support in the majority of the catalysts is [[magnesium chloride|MgCl<sub>2</sub>]]. A third component of most catalysts is a carrier, a material that determines the size and the shape of catalyst particles. The preferred carrier is [[microporous]] spheres of [[amorphous silica]] with a diameter of 30–40&nbsp;mm. During the catalyst synthesis, both the titanium compounds and MgCl<sub>2</sub> are packed into the silica pores. All these catalysts are activated with organoaluminum compounds such as [[Triethylaluminium|Al(C<sub>2</sub>H<sub>5</sub>)<sub>3</sub>]].<ref name="ref2"/>

All modern supported Ziegler–Natta catalysts designed for polymerization of propylene and higher 1-alkenes are prepared with [[titanium tetrachloride|TiCl<sub>4</sub>]] as the active ingredient and [[magnesium chloride|MgCl<sub>2</sub>]] as a support. Another component of all such catalysts is an organic modifier, usually an [[ester]] of an [[Aromatic acid|aromatic diacid]] or a [[ether|diether]]. The modifiers react both with inorganic ingredients of the solid catalysts as well as with organoaluminum cocatalysts.<ref name="ref2"/> These catalysts polymerize propylene and other 1-alkenes to highly crystalline isotactic polymers.<ref name="ref1"/><ref name="ref2"/>