Carbocatalysis
Encyclopedia
Carbocatalysis is a form of catalysis
that uses heterogeneous carbon
materials for the transformation or synthesis of organic or inorganic substrates. The catalysts are characterized by their high surface areas, surface functionality, and large, aromatic basal planes. Carbocatalysis can be distinguishable from supported catalysis (such as palladium on carbon
) in that no metal is present, or if metals are present they are not the active species.
As of 2010, the mechanisms of reactivity are not well understood.
One of the most common examples of carbocatalysis is the oxidative dehydrogenation
of ethylbenzene
to styrene discovered in the 1970's. Also in the industrial process of (non-oxidative) dehydrogenation of ethylbenzene, the potassium
-promoted iron oxide
catalyst is coated with a carbon layer as the active phase. In another early example, a variety of substituted nitrobenzenes were reduced to the corresponding aniline
using hydrazine
and graphite as the catalyst.
The discovery of nanostructured carbon allotropes such as carbon nanotubes, fullerenes, or graphene
promoted further developments. Oxidized carbon nanotubes were used to dehydrogenate n-butane to 1-butene
, and to selectively oxidize acrolein
to acrylic acid
. Fullerenes were used in the catalytic reduction of nitrobenzene to aniline in the presence of H2
. Graphene oxide was used as a carbocatalyst to facilitate the oxidation of alcohols to the corresponding aldehydes/ketones (shown in the picture), the hydration
of alkynes, and the oxidation of alkenes.
Catalysis
Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....
that uses heterogeneous carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
materials for the transformation or synthesis of organic or inorganic substrates. The catalysts are characterized by their high surface areas, surface functionality, and large, aromatic basal planes. Carbocatalysis can be distinguishable from supported catalysis (such as palladium on carbon
Palladium on carbon
Palladium on carbon, often referred to as Pd/C, is a form of palladium used for catalysis. It is usually used for catalytic hydrogenations in organic chemistry...
) in that no metal is present, or if metals are present they are not the active species.
As of 2010, the mechanisms of reactivity are not well understood.
One of the most common examples of carbocatalysis is the oxidative dehydrogenation
Dehydrogenation
Dehydrogenation is a chemical reaction that involves the elimination of hydrogen . It is the reverse process of hydrogenation. Dehydrogenation reactions may be either large scale industrial processes or smaller scale laboratory procedures....
of ethylbenzene
Ethylbenzene
Ethylbenzene is an organic compound with the formula C6H5CH2CH3. This aromatic hydrocarbon is important in the petrochemical industry as an intermediate in the production of styrene, which in turn is used for making polystyrene, a common plastic material....
to styrene discovered in the 1970's. Also in the industrial process of (non-oxidative) dehydrogenation of ethylbenzene, the potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
-promoted iron oxide
Iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g.,...
catalyst is coated with a carbon layer as the active phase. In another early example, a variety of substituted nitrobenzenes were reduced to the corresponding aniline
Aniline
Aniline, phenylamine or aminobenzene is an organic compound with the formula C6H5NH2. Consisting of a phenyl group attached to an amino group, aniline is the prototypical aromatic amine. Being a precursor to many industrial chemicals, its main use is in the manufacture of precursors to polyurethane...
using hydrazine
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
and graphite as the catalyst.
The discovery of nanostructured carbon allotropes such as carbon nanotubes, fullerenes, or graphene
Graphene
Graphene is an allotrope of carbon, whose structure is one-atom-thick planar sheets of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. The term graphene was coined as a combination of graphite and the suffix -ene by Hanns-Peter Boehm, who described single-layer...
promoted further developments. Oxidized carbon nanotubes were used to dehydrogenate n-butane to 1-butene
1-Butene
1-Butene is an organic chemical compound, linear alpha-olefin , and one of the isomers of butene. The formula is .-Stability:1-Butene is stable in itself but polymerizes exothermically. It is highly flammable and readily forms explosive mixtures with air...
, and to selectively oxidize acrolein
Acrolein
Acrolein is the simplest unsaturated aldehyde. It is produced widely but is most often immediately reacted with other products due to its instability and toxicity...
to acrylic acid
Acrylic acid
Acrylic acid is an organic compound with the formula CH2=CHCO2H. It is the simplest unsaturated carboxylic acid, consisting of a vinyl group connected directly to a carboxylic acid terminus. This colorless liquid has a characteristic acrid or tart smell. It is miscible with water, alcohols,...
. Fullerenes were used in the catalytic reduction of nitrobenzene to aniline in the presence of H2
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
. Graphene oxide was used as a carbocatalyst to facilitate the oxidation of alcohols to the corresponding aldehydes/ketones (shown in the picture), the hydration
Hydration reaction
In organic chemistry, a hydration reaction is a chemical reaction in which a hydroxyl group and a hydrogen cation are added to the two carbon atoms bonded together in the carbon-carbon double bond which makes up an alkene functional group. The reaction usually runs in a strong acidic, aqueous...
of alkynes, and the oxidation of alkenes.