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The process contrasts with homogeneous catalysis where the reagents, products and catalyst exist in the same phase. Phase distinguishes between not only solid , liquid , and gas components, but also immiscible mixtures (e.g., oil and water ), or anywhere an interface is present.
In contrast, heterogeneous catalysis describes processes where the catalysts and substrate are in distinct phases, typically solid and gas, respectively. [1] The term is used almost exclusively to describe solutions and implies catalysis by organometallic compounds. Homogeneous catalysis is an established technology that continues to evolve.
Aspects are described in an early review: "using a non-protic Lewis acid, aluminium tribromide, were able to demonstrate the truly catalytic effect of titanium by treating dinitrogen with a mixture of titanium tetrachloride, metallic aluminium, and aluminium tribromide at 50 °C, either in the absence or in the presence of a solvent, e.g. benzene.
A second class of Ziegler–Natta catalysts are soluble in the reaction medium. Traditionally such homogeneous catalysts were derived from metallocenes, but the structures of active catalysts have been significantly broadened to include nitrogen-based ligands. A post-metallocene catalyst developed at Dow Chemical. [8]
Homogeneous metallocene catalysts, e.g., derived from or related to zirconocene dichloride introduced a level of microstructural control that was unavailable with heterogeneous systems. [2] Metallocene catalysts are homogeneous single-site systems, implying that a uniform catalyst is present in the solution. In contrast, commercially important ...
Orthogonal tandem catalysis is a "one-pot reaction in which sequential catalytic processes occur through two or more functionally distinct, and preferably non-interfering, catalytic cycles". [7] This technique has been deployed in tandem alkane-dehydrogenation-olefin-metathesis catalysis [ 8 ] [ 9 ]
Oxidation catalysis is conducted by both heterogeneous catalysis and homogeneous catalysis. In the heterogeneous processes, gaseous substrate and oxygen (or air) are passed over solid catalysts. Typical catalysts are platinum, and redox-active oxides of iron, vanadium, and molybdenum.
Advanced Synthesis & Catalysis is a bimonthly peer-reviewed scientific journal established in 1999 by Wiley.It covers research on homogeneous, heterogeneous, organic, and enzyme catalysis that are key technologies to achieve green synthesis, significant contributions to the same goal by synthesis design, reaction techniques, flow chemistry, and continuous processing, multiphase catalysis ...