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Ziegler–Natta catalysts of the third class, non-metallocene catalysts, use a variety of complexes of various metals, ranging from scandium to lanthanoid and actinoid metals, and a large variety of ligands containing oxygen (O 2), nitrogen (N 2), phosphorus (P), and sulfur (S). The complexes are activated using MAO, as is done for metallocene ...
In chemistry, homogeneous catalysis is catalysis where the catalyst is in same phase as reactants, principally by a soluble catalyst in a solution. In contrast, heterogeneous catalysis describes processes where the catalysts and substrate are in distinct phases, typically solid and gas, respectively. [ 1 ]
In polymer chemistry, ring-opening metathesis polymerization (ROMP) is a type of chain-growth polymerization involving olefin metathesis. [1] The reaction is driven by relieving ring strain in cyclic olefins. [2] A variety of heterogeneous and homogeneous catalysts have been developed for different polymers and mechanisms. [3]
In chemistry, a phase-transfer catalyst or PTC is a catalyst that facilitates the transition of a reactant from one phase into another phase where reaction occurs. Phase-transfer catalysis is a special form of catalysis and can act through homogeneous catalysis or heterogeneous catalysis methods depending on the catalyst used.
The heterogeneous process ultimately failed due to catalyst inactivation and was replaced by the water-based homogeneous system for which a pilot plant was operational in 1958. Problems with the aggressive catalyst solution were solved by adopting titanium (newly available for industrial use) as construction material for reactors and pumps ...
Kartstedt's catalyst is often used in hydrosilylation. Before introduction of platinum catalysts by Speier, hydrosilylation was not practiced widely. A peroxide-catalyzed process was reported in academic literature in 1947, [9] but the introduction of Speier's catalyst (H 2 PtCl 6) was a big breakthrough. Karstedt's catalyst was later
Catalyst prepared and handled under anaerobic condition reverses the selectivity to favor the secondary boronate ester. What has been debated is the coordination of the alkene. In the dissociative mechanism, proposed by Männig and Nöth, [ 4 ] and supported by Evans and Fu [ 5 ] the coordination is accompanied by the loss of one ...
Illustrative metallocene-based coordination catalysts. Kaminsky catalysts are based on metallocenes of group 4 metals (Ti, Zr, Hf) activated with methylaluminoxane (MAO). [8] [9] Polymerizations catalysed by metallocenes occur via the Cossee–Arlman mechanism. The active site is usually anionic but cationic coordination polymerization also exists.