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The apparent activation energy of CO oxidation on supported gold powder catalysts prepared by wet methods is 2-3 kJ/mol above 333 K (60 °C) and 26-34 kJ/mol below 333 K. These energies are low, compared to the values displayed by other noble metal catalysts (80-120 kJ/mol).
Strong metal-support interaction is another case highlighting the oversimplification that heterogeneous catalysts are merely supported on an inert substance. The original evidence was provided by the finding that particles of platinum bind H 2 with the stoichiometry PtH 2 for each surface atom regardless of whether the platinum is supported or not.
Generally heterogeneous cross-coupling catalysts consist of a metal dispersed on an inorganic surface or bound to a polymeric support with ligands. Heterogeneous catalysts provide potential benefits over homogeneous catalysts in chemical processes in which cross-coupling is commonly employed—particularly in the fine chemical industry ...
Heterogeneous supported catalysts based on titanium compounds are used in polymerization reactions in combination with cocatalysts, organoaluminum compounds such as triethylaluminium, Al(C 2 H 5) 3. This class of catalyst dominates the industry. [1] Homogeneous catalysts usually based on complexes of the group 4 metals titanium, zirconium or ...
Common Lewis acid catalysts are based on main group metals such as aluminum, boron, silicon, and tin, as well as many early (titanium, zirconium) and late (iron, copper, zinc) d-block metals. The metal atom forms an adduct with a lone-pair bearing electronegative atom in the substrate, such as oxygen (both sp 2 or sp 3), nitrogen, sulfur, and ...
In traditional Ziegler–Natta catalysis, supported titanium trichloride is activated by treatment with trimethylaluminium (TMA). TMA only weakly activates homogeneous precatalysts, such as zirconocene dichloride. In the mid-1970s Kaminsky discovered that metallocene dichlorides can be activated by MAO (see Kaminsky catalyst). [6]
The reaction requires metal catalysts. Most commercially important processes employ heterogeneous catalysts. The heterogeneous catalysts are often prepared by in-situ activation of a metal halide (MCl x) using organoaluminium or organotin compounds, e.g. combining MCl x –EtAlCl 2. A typical catalyst support is alumina. Commercial catalysts ...
Other mechanisms for catalyst deactivation include: Sintering: when heated, dispersed catalytic metal particles can migrate across the support surface and form crystals. This results in a reduction of catalyst surface area. Fouling: the deposition of materials from the fluid phase onto the solid phase catalyst and/or support surfaces. This ...