The Role of Catalyst Support, Diluent and Co-Catalyst in Chromium-Mediated Heterogeneous Ethylene Trimerisation

Abstract

Sequential treatment of a previously-calcined solid oxide support (i.e. SiO2, γ-Al2O3, or mixed SiO2–Al2O3) with solutions of Cr{N(SiMe3)2}3 (0.71 wt% Cr) and a Lewis acidic alkyl aluminium-based co-catalyst (15 molar equivalents) affords initiator systems active for the oligomerisation and/or polymerisation of ethylene. The influence of the oxide support, calcination temperature, co-catalyst, and reaction diluent on both the productivity and selectivity of the immobilised chromium initiator systems have been investigated, with the best performing combination (SiO2−600, modified methyl aluminoxane-12 {MMAO-12}, heptane) producing a mixture of hexenes (61 wt%; 79% 1-hexene), and polyethylene (16 wt%) with an activity of 2403 g gCr−1 h−1. The observed product distribution is rationalised by two competing processes: trimerisation via a supported metallacycle-based mechanism and polymerisation through a classical Cossee-Arlman chain-growth pathway. This is supported by the indirect observation of two distinct chromium environments at the surface of the oxide support by a solid-state 29Si NMR spectroscopic study of the Cr{N(SiMe3)2}x/SiO2−600 pro-initiator.Electronic supplementary materialThe online version of this article (10.1007/s11244-018-0891-8) contains supplementary material, which is available to authorized users.

Ethylene Oligomerization Catalyzed by Different Homogeneous or Heterogeneous Catalysts

“…In contrast, heterogeneous catalysts can not only be separated from the product but also protect the active center of the catalyst. Cr-based heterogeneous catalysts, such as immobilizing homogeneous catalysts onto supports [202,203], dispersing them into ionic liquids [204,205], and Cr-MOFs [206,207], were reported recently.…”

“…Lamb et al [202] immobilized a Cr-based complex on oxides including SiO 2 , γ-Al 2 O 3 , and mixed SiO 2 -Al 2 O 3 to obtain supported catalysts, which can perform selective ethylene trimerization after treatment via an aluminum activator. When using SiO 2 or SiO 2 -Al 2 O 3 as the carrier, high reaction activity and moderate trimerization selectivity can be achieved, while, when using γ-Al 2 O 3 as the carrier, the reaction activity decreases significantly, and the product is mainly PE.…”

Supported Organochromium Ethylene Oligomerization Enabled by Surface Lithiation

“…Cationic chromium aryl complexes supported by diphosphine-based PNP ligands are versatile catalysts for both ethylene trimerization and tetramerization , and are active in the absence of alkylaluminum cocatalysts. On the other hand, the development of heterogeneous catalysts for ethylene oligomerization operating via the oxidative cyclization mechanism is challenging and most of the existing heterogeneous oligomerization systems are based on silica-immobilized chromium complexes. − For example, Cr­[N­(SiMe 3 ) 2 ] and isobutylaluminoxane grafted on silica afford an ethylene trimerization catalyst, although some polymer is still generated when this system is heterogenized, and researchers at British Petroleum reported a heterogeneous CrCl 3 (THF) 3 /diphosphine on a methylaluminoxane-modified SiO 2 system which produced hexenes with a high selectivity (86.2%) without significant polymer formation. , …”

Synthesis of nano Ag catalyst embeded vanadium phosphorus oxide for oxidation of styrene to benzaldehyde by hydrogen peroxide

“…There are many choices of substrate for nano metal catalysts such as carbonaceous materials, ceramics, oxides, etc. [19,21,22] which are either inert supports or active supports. The adhesion between catalyst particles and the substrate influence the morphology, distribution of active particles and stability of the catalyst.…”