A catalyst enhances the rate of a reaction. In other words, they allow a higher fraction of molecules to reach the minimum energy required for the reaction; hence, leading to the formation of more products. Catalysts are involved in the reaction, but are regenerated at the end of the reaction so that none of the catalyst is consumed.
(Copyright The Department of Chemical Engineering,
The University of Michigan, Ann Arbor, MI)
Catalysts, such as those pictured below, were first recognized in 1835 and named by J.J. Berzelius who coined the term "catalytic power" to describe the effect of catalysts on reactions.
(Copyright 2011, Saing-Gobain NorPro, Stow Ohio, used with permission)
Chemicals had been used for centuries as catalysts before catalysis was first recognized. They enhanced the fermentation process in beer and wine production. In the mid 19th century, catalysis started to be understood and the catalysis of reactions started to be studied.
Catalysts dissociate the bonds in the reactants, promoting the recombination of the reactant atoms and as a result speed the reaction. The catalyst itself is eventually regenerated by the reaction.
This "catalytic power" is due to free bonding sites on the surface of the catalyst that can form chemical bonds with one or more of the reactant molecules, allowing the reactions to occur with greater ease. The actual mechanisms depend on the reactants and catalysts involved.
The animation below shows CO reacting with O 2 with the help of a metal catalyst. Oxygen (white) dissociates on the catalyst surface. Carbon (red), which is already attracted to the catalytic surface, picks up an unbonded oxygen atom to form CO 2 .
Catalysis is divided into two categories, heterogeneous and homogeneous. In heterogeneous catalysis, the catalysts and reactants are in different phases, while in homogeneous catalysis they are in a single phase. Industrial processes use heterogeneous catalysts almost exclusively.
Many types of materials can serve as catalysts. Industrially, strong acids and bases, metal oxides and sulfides, metals, and free radical formers are the most useful. Catalysts are typically made from nickel, copper, osmium, platinum, and rhodium.
Industrial catalysts are usually introduced into a reaction through the use of a support , such as the ones shown below. The catalytic material coats and is adsorbed into the pellet. Typically only 0.1- 20% of the surface is active. The catalysts shown below are made of precious metal on ceramic beads and are used in an electric catalytic oxidizer that treats air streams contaminated with volatile organic compounds (VOCs).
(Copyright Falmouth Products Inc., Falmouth, MA)
Typical pellets are highly porous, with over 100 square centimeters of surface area per cubic centimeter. Pores are between two and 100 nanometers in diameter. The high surface area increases the contact between the reactant and the catalyst, increasing the reaction rate. The contact is further enhanced by saturating the support with the reaction mixture.
(Copyright Global Catalyst & Process Technology Mgt, PLLC, Waynesville, NC)
Catalysts are used in the production of over 20% of all industrial products and 90% of all chemicals and materials produced worldwide. The single biggest user of catalysts is the petroleum industry. The oil refinery pictured uses catalysts in four processes: catalytic reforming, hydrotreatment, fluid catalytic cracking, and alkylation.
- Catalytic reforming uses metal alloys such as platinum to boost the octane ratings of gasoline by reforming the carbon chains in petroleum.
- Hydrotreatment is the process of adding hydrogen gas in the presence of mixed metal sulfides on a carrier to improve gas qualities, protect downstream catalysts and improve emissions by saturating bonds in long hydrocarbons.
- Catalytic cracking uses a silica-alumina matrix with zeolite crystals (crystalline alumino silicates) to reduce the length of hydrocarbon chains into usable shorter chains, such as octane.
- Alkylation is the process of reacting shorter unsaturated hydrocarbon chains in the presence of a catalyst to produce high octane branched hydrocarbons, gasoline.
(Copyright Sierra Monitor Corporation, Milpitas, CA)
Catalysts are also used to produce cleaner products, such as transportation fuels and energy sources, in a more environmentally friendly way. Because emission regulations surrounding fuels and air pollution are getting stricter, the demand for catalyst development for these applications increases every year. For example, cleaner fuels require an extremely low concentration of sulfur. Zeolite catalysts (microporous, aluminosilicate minerals) for fluid-catalytic cracking (FCC) and hydro-cracking, and base metal hydrogenation catalysts, such as nickel, cobalt, and molybdenum, are used for desulfurization. Likewise, air emission regulations are constantly becoming more rigorous, and effective air-pollution-control catalysts are needed, especially those for NO x . Heterogeneous catalytic materials are used in processes that focus on additives used by FCC processes to catalytically convert the oxides of sulfur, nitrogen, and carbon monoxide to inert materials.
- Speed up reactions.
- Not consumed by reaction.
- Can be manipulated to fit needs.
- Increase efficiency and selectivity of reactions.
- Can be expensive.
- Must be removed from product.
Ceramatec, Inc. , Salt Lake City, UT
Falmouth Products Inc. , Falmouth, MA
Global Catalyst & Process Technology Mgt, PLLC , Waynesville, NC
Saing-Gobain NorPro , Stow, OH
Sierra Monitor Corporation , Milpitas, CA
LePree, Joy. "Cleaning Up with Catalysts." Chemical Engineering January 2008: 21-24. Print.
Bowker, Michael. The Basis and Applications of Heterogeneous Catalysis . New York: Oxford University Press, 1998. Print.
Heinemann, H. "A Brief History of Industrial Catalysis." Catalysis- Science and Technology . Ed. John R. Anderson and Michael Boudart. New York: Springer-Verlag, 1981: 1-41. Print.
Kapp, Martin. "What Catalyst and Why?" Catalysis in Practice . Ed. Charles H. Collier. New York: Reinhold Publishing, 1957: 1-48. Print.
Upson, L. L. and D. A. Lomas "Catalysts." Concise Encyclopedia of Chemical Technology . 4th ed, 1999. Print.