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Difference between revisions of "Heterogeneous catalysis"
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Heterogeneous catalysis (view source)
Revision as of 14:29, 17 January 2022
, 14:29, 17 January 2022→Process and technologies
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[[Image:Hydrogenation on catalyst.svg|thumb|upright|Hydrogenation of ethene on a catalytic solid surface; (1) Adsorption, (2) Reaction, (3) Desorption]] | [[Image:Hydrogenation on catalyst.svg|thumb|upright|Hydrogenation of ethene on a catalytic solid surface; (1) Adsorption, (2) Reaction, (3) Desorption]] | ||
A wide range of processes and technologies can make use of heterogeneous catalysts. Examples are [[pyrolysis]], hydro-processing, [[oxidation]], amination, dehydration, [[hydrolysis]], (trans)esterification, and isomerisation.<ref name=":1" /> The most common heterogeneous catalysts are heterogeneous solid base catalysts and heterogeneous solid acid catalysts. Base catalysts have a high concentration of basic sites that ensures the catalytic activity, often from Ba, Ca, Mg, and Sr and can be mixed or doped. Soap formation is a recurring drawback of these systems. Acid catalysts get their activity either from Brønsted or Lewis acidity and are commonly zirconia, silica, zeolites or zeotype materials. Major advantages of heterogeneous catalysis is the ease of separation, recyclability and high selectivity.<ref name=":0" /> Current development for future heterogeneous catalytic systems are in metal-organic frameworks (MOFs), magnetic catalysts, and solid phase ionic liquids.<ref name=":1" /> | A wide range of processes and technologies can make use of heterogeneous catalysts. Examples are [[pyrolysis]], hydro-processing, [[oxidation]], amination, dehydration, [[hydrolysis]], (trans)esterification, and isomerisation.<ref name=":1" /> The most common heterogeneous catalysts are heterogeneous solid base catalysts and heterogeneous solid acid catalysts. Base catalysts have a high concentration of basic sites that ensures the catalytic activity, often from Ba, Ca, Mg, and Sr and can be mixed or doped. Soap formation is a recurring drawback of these systems. Acid catalysts get their activity either from Brønsted or Lewis acidity and are commonly zirconia, silica, zeolites or zeotype materials. Major advantages of heterogeneous catalysis is the ease of separation, recyclability and high selectivity.<ref name=":0" /> Current development for future heterogeneous catalytic systems are in metal-organic frameworks (MOFs), magnetic catalysts, and solid phase ionic liquids.<ref name=":1" /> | ||
Some large-scale industrial processes incorporating heterogeneous catalysts are listed below:<ref>taken from [[:en:Heterogeneous catalysis|Heterogeneous catalysis]] in wikipedia.</ref> | |||
{| class="wikitable" style = "text-align:center" | |||
|- | |||
!Process | |||
!Reactants, Product/s (not balanced) | |||
!Catalyst | |||
!Comment | |||
|- | |||
|Sulfuric acid synthesis (Contact process) | |||
|SO<sub>2</sub> + O<sub>2</sub>, SO<sub>3</sub> | |||
|vanadium oxides | |||
|Hydration of SO<sub>3</sub> gives H<sub>2</sub>SO<sub>4</sub> | |||
|- | |||
|Ammonia synthesis (Haber–Bosch process) | |||
|N<sub>2</sub> + H<sub>2</sub>, NH<sub>3</sub> | |||
|iron oxides on alumina (Al<sub>2</sub>O<sub>3</sub>) | |||
|Consumes 1% of world's industrial energy budget<ref name=":02" /> | |||
|- | |||
|Nitric acid synthesis (Ostwald process) | |||
|NH<sub>3</sub> + O<sub>2</sub>, HNO<sub>3</sub> | |||
|unsupported Pt-Rh gauze | |||
|Direct routes from N<sub>2</sub> are uneconomical | |||
|- | |||
|Hydrogen production by Steam reforming | |||
|CH<sub>4</sub> + H<sub>2</sub>O, H<sub>2</sub> + CO<sub>2</sub> | |||
|Nickel or K<sub>2</sub>O | |||
|Greener routes to H<sub>2</sub> by water splitting actively sought | |||
|- | |||
|Ethylene oxide synthesis | |||
|C<sub>2</sub>H<sub>4</sub> + O<sub>2</sub>, C<sub>2</sub>H<sub>4</sub>O | |||
|silver on alumina, with many promoters | |||
|Poorly applicable to other alkenes | |||
|- | |||
|Hydrogen cyanide synthesis (Andrussov oxidation) | |||
|NH<sub>3</sub> + O<sub>2</sub> + CH<sub>4</sub>, HCN | |||
|Pt-Rh | |||
|Related ammoxidation process converts hydrocarbons to nitriles | |||
|- | |||
|Olefin polymerization Ziegler–Natta polymerization | |||
|propylene, polypropylene | |||
|TiCl<sub>3</sub> on MgCl<sub>2</sub> | |||
|Many variations exist, including some homogeneous examples | |||
|- | |||
|Desulfurization of petroleum (hydrodesulfurization) | |||
|H<sub>2</sub> + R<sub>2</sub>S (idealized organosulfur impurity), RH + H<sub>2</sub>S | |||
|Molybdenum-Cobalt on alumina | |||
|Produces low-sulfur hydrocarbons, sulfur recovered via the Claus process | |||
|} | |||
==Product== | ==Product== | ||