Editing Catalysis (section)

==Homogeneous catalysis==
{{Main|Homogeneous catalysis}}
Homogeneous catalysts function in the same phase as the reactants. Typically homogeneous catalysts are dissolved in a solvent with the substrates. One example of homogeneous catalysis involves the influence of [[hydrogen|H]]{{sup|+}} on the [[esterification]] of carboxylic acids, such as the formation of [[methyl acetate]] from [[acetic acid]] and [[methanol]].<ref>Behr, Arno (2002) "Organometallic Compounds and Homogeneous Catalysis" in Ullmann's ''Encyclopedia of Industrial Chemistry'', Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a18_215}}</ref> High-volume processes requiring a homogeneous catalyst include [[hydroformylation]], [[hydrosilylation]], [[hydrocyanation]]. For inorganic chemists, homogeneous catalysis is often synonymous with [[organometallic chemistry|organometallic catalysts]].<ref>Elschenbroich, C. (2006) ''Organometallics''. Wiley-VCH: Weinheim. {{ISBN|978-3-527-29390-2}}</ref> Many homogeneous catalysts are however not organometallic, illustrated by the use of cobalt salts that catalyze the oxidation of [[p-xylene]] to [[terephthalic acid]].

===Organocatalysis===
{{Main|Organocatalysis}}

Whereas transition metals sometimes attract most of the attention in the study of catalysis, small organic molecules without metals can also exhibit catalytic properties, as is apparent from the fact that many [[enzyme]]s lack transition metals. Typically, organic catalysts require a higher loading (amount of catalyst per unit amount of reactant, expressed in [[mol%]] [[amount of substance]]) than transition metal(-ion)-based catalysts, but these catalysts are usually commercially available in bulk, helping to lower costs. In the early 2000s, these organocatalysts were considered "new generation" and are competitive to traditional [[metal]](-ion)-containing catalysts. 

Organocatalysts are supposed to operate akin to metal-free enzymes utilizing, e.g., noncovalent interactions such as [[hydrogen bonding]]. The discipline organocatalysis is divided into the application of covalent (e.g., [[proline]], [[4-Dimethylaminopyridine|DMAP]]) and noncovalent (e.g., [[thiourea organocatalysis]]) organocatalysts referring to the preferred catalyst-[[substrate (chemistry)|substrate]] [[binding (molecular)|binding]] and interaction, respectively. The Nobel Prize in Chemistry 2021 was awarded jointly to Benjamin List and David W.C. MacMillan "for the development of asymmetric organocatalysis."<ref>{{cite web |title=The Nobel Prize in Chemistry 2021 |website=NobelPrize.org |url=https://www.nobelprize.org/prizes/chemistry/2021/summary/}}</ref>

===Photocatalysts===
{{Main|Photocatalysis}}
Photocatalysis is the phenomenon where the catalyst can receive light to generate an [[excited state]] that effect redox reactions.<ref>{{cite journal |title=Introduction: Photochemical Catalytic Processes |year=2022 |last1=Melchiorre |first1=Paolo |journal=Chemical Reviews |volume=122 |issue=2 |pages=1483–1484 |pmid=35078320 |doi=10.1021/acs.chemrev.1c00993 |doi-access=free |s2cid=246287799}}</ref> [[Singlet oxygen]] is usually produced by photocatalysis. Photocatalysts are components of [[dye-sensitized solar cell]]s.

===Enzymes and biocatalysts===
{{Main|Enzyme catalysis}}

In biology, [[enzyme]]s are protein-based catalysts in [[metabolism]] and [[catabolism]]. Most biocatalysts are enzymes, but other nonprotein-based classes of biomolecules also exhibit catalytic properties including [[ribozyme]]s, and synthetic [[deoxyribozyme]]s.<ref>Nelson, D.L. and Cox, M.M. (2000) ''Lehninger, Principles of Biochemistry'' 3rd Ed. Worth Publishing: New York. {{ISBN|1-57259-153-6}}.</ref>

Biocatalysts can be thought of as an intermediate between homogeneous and heterogeneous catalysts, although strictly speaking soluble enzymes are homogeneous catalysts and [[biological membrane|membrane]]-bound enzymes are heterogeneous. Several factors affect the activity of enzymes (and other catalysts) including temperature, pH, the concentration of enzymes, substrate, and products. A particularly important reagent in enzymatic reactions is water, which is the product of many bond-forming reactions and a reactant in many bond-breaking processes.

In [[biocatalysis]], enzymes are employed to prepare many commodity chemicals including [[high-fructose corn syrup]] and [[acrylamide]].

Some [[monoclonal antibodies]] whose binding target is a stable molecule that resembles the transition state of a chemical reaction can function as weak catalysts for that chemical reaction by lowering its activation energy.<ref>[https://web.archive.org/web/20130821044547/http://www.documentroot.com/2010/03/catalytic-antibodies-simply-explained.html Catalytic Antibodies Simply Explained]. Documentroot.com (2010-03-06). Retrieved on 2015-11-11.</ref> Such catalytic antibodies are sometimes called "[[abzyme]]s".