Heterogeneous Catalytic Chemistry by Example of Industrial Applications

Article

pubs.acs.org/jchemeduc

Heterogeneous Catalytic Chemistry by Example of Industrial Applications Josef Heveling* Department of Chemistry, Tshwane University of Technology, Private Bag X680, Pretoria 0001, South Africa

ABSTRACT: Worldwide, more than 85% of all chemical products are manufactured with the help of catalysts. Virtually all transition metals of the periodic table are active as catalysts or catalyst promoters. Catalysts are divided into homogeneous catalysts, which are soluble in the reaction medium, and heterogeneous catalysts, which remain in the solid state. A heterogeneous metal catalyst typically consists of the active metal component, promoters, and a support material. In some cases, the metallic state itself forms the active ingredient. However, this situation is largely restricted to precious metal catalysts and to some base metals used under reducing conditions. In most cases and especially in homogeneous catalysis, it is a metal compound or a complex that forms the active catalyst. Catalysis can be rather puzzling as a given metal can catalyze a variety of different chemical transformations, while the same substrate, passed over different catalysts, can give different products. It is therefore helpful to be familiar with the fundamentals of catalytic science before being exposed to the uncountable applications, which form the backbone of industrial chemistry. Examples of practical importance are used in this paper to highlight important principles of catalysis. KEYWORDS: General Public, Public Understanding, Upper-Division Undergraduate, Curriculum, Inorganic Chemistry, Catalysis, Green Chemistry, Industrial Chemistry

catalyst is a substance that accelerates the rate of a • In 2005 the value of the goods produced with the help of A chemical reaction. The catalyst is not consumed and catalysts amounted to ∼900 billion US$.3 therefore does not appear in the overall reaction equation. A Looking at these figures, one has to keep in mind that catalysts catalyst promoter is an additive that improves the performance employed for environmental abatement processes, such as of a catalyst, but has no catalytic activity for a given chemical automotive exhaust catalysts, do not produce any goods of conversion. Often the catalyst is written above the reaction economic value. A breakdown of catalyst usage by industry arrow in square brackets. This indicates that a catalyst is needed sectors indicates that there is an almost even distribution across for the reaction to attain equilibrium within a reasonable time. ff fi four di erent sectors, namely, (i) the polymer industry (21%); For example, the esteri cation of carboxylic acids with alcohols (ii) coal, oil, and gas refining (22%); (iii) manufacturing of takes place in the presence of acids or bases, as does the reverse chemicals (27%); and (iv) environmental applications (30%).2 reaction, the hydrolysis of esters. In the equation below (Scheme 1), the acid shows above the reaction arrow to ■ INDUSTRIAL CATALYTIC CONVERTERS indicate that this reaction is acid catalyzed. Various reactor types have been designed to facilitate catalytic Scheme 1. Acid-Catalyzed Esterification conversions on an industrial scale. Four examples are given in Figure 1.4 Reactor A is a stirred tank reactor operated batchwise. The catalyst is dissolved in the liquid phase, and it could be an acid or a base, a metal salt, or a metal−organic complex. Shown is a ruthenium alkylidene complex, which is active for the olefin metathesis reaction.5 Catalysis in solution is referred to as homogeneous catalysis. Homogeneous catalysts are usually more active and selective than heterogeneous catalysts. ■ ECONOMIC BACKGROUND They are also easier to tailor for specific purposes, as the The economic importance of catalysis reflects in the following reaction mechanism is often well understood. The major numbers: disadvantage of homogeneous catalysis lies in the fact that it is ffi • More than 85% of all chemical products are manufac- di cult to separate the products from the catalyst, as the tured with the help of catalysts.1 catalyst is present in the same phase. Also, homogeneous • 15−20% of the economic activities in industrialized catalysts do not lend themselves easily for continuous countries depend directly on catalysis.2 operations. However, these problems can be overcome by • The commercial value of the catalysts produced annually amounts to ∼14 billion US$.2 Published: October 9, 2012

In the oil reﬁning industry, almost all chemical conversions are catalyzed, and the E-factor is less than 0.1. However, when ascending the value creation chain in the chemical industry, the impact of catalysis decreases. The synthesis of pharmaceuticals, for example, is clearly dominated by traditional, multistep, stoichiometric organic chemistry, and burdened with a high E- factor; the quantity of waste produced can exceed the quantity of the targeted active pharmaceutical ingredient by a factor higher than 25 (see Figure 2).

Figure 2. The impact of catalysis on the environmental E-factor. Figure 1. Some catalytic reactors (a, gaseous feed; b, gaseous or liquid product; c, liquid feed; d, liquid product; e, off-gas; f, catalyst; g, Another convenient measure for the environmental impact of coolant). Examples for the catalysts used in each reactor type are chemical conversions is the atom utilization.7,8 Calculation of fi pictured at the bottom of the gure. See the text for a detailed the atom utilization (AU) is based on molecular weights (MW) explanation. and defined as follows: MW of desired product immobilizing homogeneous catalysts onto heterogeneous AU = supports. For a successful heterogenization of a transition- Sum of MWs of all products formed in the stoichiometric equation metal complex, the reaction mechanism should predict that the The usefulness of the atom utilization for the comparison of metal ligand chosen for bonding to the support remains firmly different chemical processes is demonstrated by example of two attached to the metal. The cyclopentadienyl ligand is an routes to niacin or niacinamide. Niacin or nicotinic acid is a example for such a ligand.6 vitamin of the B group. In vivo, the acid is converted into the Reactors B, C, and D (Figure 1) are used for heterogeneous amide and both can be used as nutritional supplements. Lonza catalytic processes. Example B represents a sparged stirred tank AG (Switzerland) is a major supplier and has developed two reactor for gas−liquid reactions. The catalyst is suspended in routes. The classical route is used in Switzerland, while a new powder form. Shown below the reactor is a precious-metal catalytic route is operated by Lonza Guangzhou in China. The catalyst supported on activated carbon. The catalyst can readily classical route starts with acetaldehyde and ammonia (Scheme be filtered off and reused until it is no longer of sufficient 2). These are converted into 5-ethyl-2-methylpyridine by a activity. Spend metal catalysts are normally returned to the catalyst manufacturer for metal recovery. Examples C and D Scheme 2. Classical Route to Nicotinic Acid (Lonza AG, show fixed-bed reactors. These operate in a continuous mode. Switzerland) The solid catalyst is stationary and the gaseous or liquid feed is passed over the catalyst bed. Multitube reactors (D) allow for efficient heat removal in the case of exothermic reactions. Heterogeneous catalysts for fixed-bed operations come in many different forms, as determined by the macro- and the microkinetics of the process. The artistic composition of examples shown below the two reactors was taken from a Clariant, formerly, Süd-Chemie catalogue, with permission. Clariant is a catalyst manufacturer. Other companies producing catalysts for the chemical industry and other applications include BASF, Evonic, Johnson Matthey, Heraeus and Haldor- Topsoe. Reactor types used for catalytic conversions are not limited to those shown in Figure 1. See Henkel4 for a more comprehensive selection.

■ ENVIRONMENTAL IMPACT OF CATALYSIS Tschitschibabin pyridine synthesis,9 followed by oxidation with Catalysis is inherently a green technology. This is clearly nitric acid.10 As Scheme 2 shows, the environmental impact of demonstrated by the influence catalysis has on the environ- this route is contained by recycling of the nitrous oxide, but two mental factor (E-factor).7 The E-factor is defined as mass of carbons are lost as carbon dioxide. The overall atom utilization waste produced per mass of desired product. is 37%. It is important to keep in mind that the atom utilization kg of waste (in contrast to the E-factor) does not account for losses caused E = by low selectivities, as these are not reflected in the overall kg of desired product reaction equation. If a reactant A undergoes a variety of parallel

1531 dx.doi.org/10.1021/ed200816g | J. Chem. Educ. 2012, 89, 1530−1536 Journal of Chemical Education Article or consecutive reactions and B is the desired product, the selectivity S to B (in %) is deﬁned as Number of moles of A converted to B S = 100% B Total number of moles of A converted The catalytic route (Scheme 3) starts with 2-methylpentanediamine, which is cyclized to 3-methylpiperidine over an

Scheme 3. Modern Catalytic Route to Niacinamide (Lonza Guangzhou)

Figure 3. Schematic comparison of the thermodynamics and kinetics of a catalyzed versus an uncatalyzed reaction.

substrates in the gas phase. Wilhelm Normann proved him wrong; in 1902, he patented the catalytic hydrogenation of fats and oils in the liquid phase.15 By 1914 not less than 25 plants for the saturation of fats and oils (fat hardening) were running worldwide, mainly for the production of margarine and shortening.16,17 ■ MECHANISTIC ASPECTS OF CATALYSIS ON METAL acidic catalyst. 3-Methylpiperidine is dehydrogenated to 3- SURFACES 11 picoline over palladium. It follows an ammonoxidation Today’s understanding of double-bond hydrogenation is based reaction to 3-cyanopyridine using a vanadium oxide containing on the mechanism originally proposed by Horiuti and Polanyi18 catalyst. Finally, selective enzymatic nitrile hydrolysis leads to for the hydrogenation of ethylene on a Pt(111) surface (Figure 12 pharma-grade niacinamide. Notably, the ammonia set free in 4). This mechanism is instructive, as the principle reaction steps the first step is re-incorporated in the third step. The only byproducts are hydrogen and water, and the overall atom utilization is 75%. Hydrogen can be recovered for further use, and water is environmentally beneficial. The process shown is therefore a prime example of modern green chemistry. The starting material, 2-methylpentanediamine, is marketed by Invista (previously DuPont) under the trade name Dytek A. It is obtained by hydrogenation of 2-methylglutaronitrile, which is a structural isomer of adipodinitrile and, therefore, a byproduct of the Nylon 6.6 manufacturing route. ■ THERMODYNAMIC AND KINETIC ASPECTS OF CATALYSIS The thermodynamic and kinetic implications of catalysis are schematically demonstrated in Figure 3. A catalyst provides a new route with a lower Gibbs energy of activation (ΔG⧧) for the product formation from given starting materials (reactants).13 In this way, a catalyst accelerates the reaction. The ⊖ Figure 4. Schematic presentation of the mechanism for the Gibbs energy for the reaction (ΔG ) remains unchanged. This hydrogenation of ethylene on a platinum surface. means a reaction that is thermodynamically unfavorable cannot be made favorable with the help of a catalyst. (Catalysis is a kinetic, not a thermodynamic, phenomenon.) All the catalytic ff intermediates of the reaction must be less stable than the involved o er a good starting point for the understanding of product. If an “intermediate” is more stable than the desired many other reactions taking place on metal surfaces. product, the reaction will stop there (dotted line in Figure 3), The following steps describe the mechanism: and this intermediate will be the final product. • Physisorption of the reactants on the metal surface. The addition of hydrogen to the double bond of ethylene, for (Physisorption takes place via van der Waals forces.) example, is thermodynamically favorable, but does not proceed • Chemisorption of the reactants. (Chemisorption involves at room temperature at any appreciable rate. At the turn of the the formation of chemical bonds with the catalyst 19th century, Paul Sabatier discovered that such reactions could surface.) Ethylene forms an equilibrium between the π- be greatly accelerated by the addition of finely divided nickel.14 bonded and the di-σ-bonded form, and the H−H bond However, he maintained that this would only be possible with of hydrogen is cleaved. According to Somorjai,19 it is

1532 dx.doi.org/10.1021/ed200816g | J. Chem. Educ. 2012, 89, 1530−1536 Journal of Chemical Education Article

mainly π-bonded ethylene that, in the following step, strike the correct balance and provide the optimum strength of reacts further to the ethyl intermediate. bonding between the reactant and the catalyst surface for the • Formation of the ethyl intermediate. This step must be reaction to occur. reversible, as the complete range of deuterated ethanes For ethylene hydrogenation the situation translates into the − 23,24 (and not only DH2C CH2D) is observed in case D2 is picture shown in Figure 6. First-row transition metals and 20 used instead of H2. • Formation of the second C−H bond. • Desorption of the product. The key step is the activation of the reactants by chemisorption to the platinum surface. This facilitates the catalytic route of lower activation energy for the formation of the products. Sabatier postulated that a good catalyst provides an optimum strength of bonding between the reactants and the catalyst surface (Sabatier’s principle).21 Both too weak and too strong bonds will slow down or prevent the reaction. This principle was convincingly demonstrated by Rootsaert and Sachtler,22 as illustrated in Figure 5. The model reaction is the decomposition

Figure 6. Rate of ethylene hydrogenation over various metals relative to rhodium (Rh = 1; adapted from ref 24).

second- and third-row transition metals appear on separate volcano curves. The group VIII metals (periodic groups 8−10) are most active and among these the platinum group metals. It is well-known from practical applications that base metals are less active hydrogenation catalysts than the more expensive platinum group metals (PGMs). Base metals generally require more stringent reaction conditions than PGMs to achieve acceptable results. However, for bulk chemical applications, the catalyst price is a determining factor, and for this reason, nickel and cobalt are often preferred to precious metal catalysts (Ru, Rh, Pd, and Pt). It should be mentioned that the exact chemical nature of the chemisorbed species that play an active role in a given catalytic conversion is often difficult to establish. The precise molecular structure of the intermediates depends on many factors. These Figure 5. Demonstration of Sabatier’s principle by example of the include dehydrogenation of formic acid. The plot shows the reaction • Composition of the catalytically active metal or alloy. temperature required to achieve a given rate in the metal-catalyzed • Crystallite size of the metal or alloy. dehydrogenation reaction versus the enthalpy of formation of the • metal formates (adapted from ref 22). Exact metal surface structure (e.g., type of exposed crystal phase, presence of kinks and steps). • Adsorbate induced restructuring.19 of formic acid to carbon dioxide and hydrogen over various • metals. It is reasonable to assume that the metal formate shown Presence of other chemisorbed species. • Nature of the catalyst support. is the reaction intermediate. The strength of the bond between • the formate and the catalyst surface can be estimated by the Presence of catalyst promoters. Δ ⊖ • Temperature and pressure. enthalpy of formation ( fH ) of the corresponding metal Δ ⊖ fl formate salt. fH is plotted on the x axis of the graph shown A catalyst surface must be seen as a exible, dynamic system in Figure 5. The reaction temperature required to reach a that is able to accommodate a sequence of catalytic prefixed reaction rate (log r = 0.8) for the decomposition of intermediates. The multiplicity of possible surface sites makes formic acid over the corresponding metal catalysts appears on it difficult to determine the exact chemical environment of each the y axis. The result is a volcano curve. The most active metals intermediate that contributes to the catalytic cycle. For an appear at the top of the volcano curve at the lowest advanced treatment of this important aspect of heterogeneous 25 temperatures required to achieve the preset reaction rate. To catalysis, see van Santen and Neurock. the left (Au and Ag), bond formation between the catalyst surface and the formate is too weak, as indicated by the ■ CONVERSIONS BY METALLIC-STATE CATALYSIS Δ ⊖ corresponding fH values; to the right (W, Fe, Co, Ni, and It is necessary to clearly distinguish between catalysis by metals Cu), the enthalpy of formation is highly negative and bond and catalysis in the metallic state. The general term “metal formation is too strong. In the first case, the intermediate does catalysis” is usually understood to include catalysis by metal not form at a sufficiently high rate; in the second case, the compounds, such as metal oxides, salts, and organometallic intermediate is too stable and does not decompose at a complexes. Homogeneous transition-metal catalysis is always sufficiently high rate. The platinum group metals in the middle facilitated by metal compounds. A border case between

1533 dx.doi.org/10.1021/ed200816g | J. Chem. Educ. 2012, 89, 1530−1536 Journal of Chemical Education Article homogeneous and heterogeneous catalysis would be the synthesis. As indicated in Figure 7, a line drawn across the catalysis induced by colloidal nanoparticles kept in suspen- periodic table separates copper and nickel, separates the base sion.26 Only groups VIII and IB of the periodic table (all the metals from the PGMs up to ruthenium, divides ruthenium metals shown in Figure 7) display catalytic activity of practical from rhodium and osmium, and finally crosses down between osmium and rhenium. Under normal catalytic reaction conditions, metals to the left of this line dissociatively chemisorb carbon monoxide, whereas metals to the right will chemisorb CO molecularly (without breaking the carbon− oxygen bond).29 In other words, on iron, cobalt, and nickel CO dissociates, whereas it remains undissociated on the coinage metals (Cu, Ag, and Au) and the PGMs (except Ru). Regardless of the detailed mechanisms involved,29 the full hydrogenation of undissociated CO over a copper catalyst leads to methanol, whereas the hydrogenation over the base metals iron, cobalt, and nickel leads to hydrocarbons and water. The fact that commercial nickel catalysts can produce methane with a selectivity of up to 96% is explained by the high abundance of chemisorbed hydrogen relative to chemisorbed carbon (carbidic surface carbon) on a nickel surface. As a result, almost all the surface carbon is rapidly hydrogenated to methane.29 This is in contrast to the situation found on iron Figure 7. Synthesis gas (CO/H2) products obtained over various (and cobalt). The coverage by carbidic carbon is extensive and metals depending on the mode of CO chemisorption (associative or the reduced availability of hydrogen favors hydrocarbon chain dissociative; chemisorption of hydrogen not shown). growth to give alkanes, and unsaturated compounds (olefins) form as byproducts. In terms of Sabatier’s principle iron and significance in the metallic state, especially for hydrogenation cobalt provide the optimum bond strength for the chemisorbed and oxidation reactions. Other transition elements are too species to form Fischer−Tropsch products, whereas nickel difficult to reduce and to maintain in the metallic state.24 In the provides the optimum bond strength for the formation of metallic state, iron, cobalt, nickel, copper, and ruthenium methane. catalyze hydrogenation reactions, including the hydrogenation The reverse reaction of methanation (double arrow in Figure or hydrogenolysis of carbon monoxide. (Hydrogenolysis, in 7) is known as steam reforming and is of even greater industrial contrast to hydrogenation, involves the cleavage of an importance. Most of the synthesis gas used for processes such interatomic connection in the substrate.) Iron and ruthenium as methanol synthesis, Fischer−Tropsch synthesis, and hydro- are unique in their capability of converting nitrogen to formylation (the conversion of olefins into aldehydes) is ammonia, a reaction that can be regarded as the hydrogenolysis produced by nickel-catalyzed steam reforming. of N2. Silver is used for some large-scale selective oxidation reactions, such as the conversion of ethylene to ethylene oxide ■ AUTOMOTIVE EXHAUST CATALYSIS and the oxidation of methanol and ethanol to the corresponding aldehydes. In contrast, oxidations over Rh, Pd, As indicated above, oxidations over Rh, Pd, Ir, and Pt are prone Ir, and Pt are prone to result in deep oxidation, which is the to result in deep oxidation. Environmental abatement catalysts make use of this. The most important single application is total oxidation to CO2 and water. These four metals are also extremely useful for many conversions involving hydrogen, probably automotive exhaust catalysis. It is a remarkable such as hydrogenations, dehydrogenations, hydrogenolyses, and achievement that the deep oxidation of hydrocarbons and carbon monoxide and the reduction of nitrous oxides can be naphtha reforming. The catalytic activity of gold appears to be 30 restricted to the nanostate,27 as confirmed by numerous more done in a single catalytic converter. This is possible by the use recent reports.28 of platinum or palladium or both combined with rhodium. A Metallic-state catalysis over group VIII and IB elements schematic presentation is given in Figure 8. Rhodium is able to includes many important large-scale processes. Examples are dissociatively adsorb NO in preference to O2,whereas − palladium and platinum are responsible for the splitting of ammonia synthesis (Fe), ammonia oxidation (Pt Rh), 31 Fischer−Tropsch synthesis (Fe, Co), methanol synthesis oxygen. The chemisorbed nitrogen atoms combine to N2, and (Cu), and refinery processes such as platforming. the chemisorbed oxygen atoms oxidize carbon monoxide and hydrocarbons (HC) to CO2 and water. ■ METAL-DEPENDENT PRODUCT FORMATION FROM SYNTHESIS GAS

The conversion of synthesis gas (mixtures of CO/H2 in diﬀerent ratios) provides an interesting case concerning the change in product selectivity depending on the catalytic element used. This is demonstrated in Figure 7. The product selectivity changes along the ﬁrst transition-metal series from left to right. Iron and cobalt (and also ruthenium) convert synthesis gas into a mixture of hydrocarbons by a process Figure 8. Schematic presentation of the key aspects of an automotive known as Fischer−Tropsch synthesis. Nickel is a selective catalytic converter (HC = hydrocarbons; adsorption of CO and HC methanation catalyst, and copper is used for methanol not explicitly shown).

1534 dx.doi.org/10.1021/ed200816g | J. Chem. Educ. 2012, 89, 1530−1536 Journal of Chemical Education Article

The introduction of the automotive exhaust catalyst shows Scheme 5. Selective Oxidation of Hydroxymethylimidazoles that legislative pressure can trigger innovative solutions and to Formylimidazoles create business opportunities on a large scale (even for metal brokers and speculators). To understand some of the price fluctuation seen for rhodium over the last four decades,32 it has to be kept in mind that the annual mining output of rhodium is only about 25 tons. This constitutes ca. 1% of the annual gold production. The annual production of platinum amounts to approximately 130 tons. In 2008, more than 75% of the total rhodium output was used for the manufacturing of autocatalysts.33 ■ PEDAGOGICAL ASPECTS The content of this article can be used as the basis for an ■ SELECTIVE OXIDATION CATALYSIS UNDER MILD introduction to heterogeneous catalysis. For example, it could CONDITIONS lay the foundation for a course on descriptive heterogeneous Deep oxidation, or over oxidation, is likely to occur with PGMs catalysis or industrial process chemistry. It also could serve as under oxidative conditions, unless special precautions are taken. an amendment to a course on homogeneous catalysis. Students However, for selective oxidation reactions, high-oxidation-state are provided with a background on economic and ecological base-metal oxides can be used as catalysts. These must be able aspects of catalysis, types of catalysts used in industrial practice, fi to switch between two oxidation states (redox catalysis). modi cation of catalysts (to improve selectivity), the importance of surface chemistry for the understanding of Examples are MoO3,V2O5, and Sb2O5. The reactions take place at elevated temperatures in the gas phase. These conditions can catalytic reactions at a molecular level, and thermodynamic and be prohibitive for fine chemical applications, due to the kinetic implications. Examples of industrial importance are used temperature sensitivity of complex organic molecules. However, for demonstration purposes. After they have been introduced to for applications in the fine chemicals industry, palladium and catalysis using the concept of this paper, learners should be able platinum catalysts can be modified by incorporation of bismuth to answer the following question: Why do certain metals or lead, resulting in improved selectivity for partial oxidations. selectively catalyze certain transformations? Although the exact role of bismuth and lead is still a matter of Parts of this paper could be given as exercises. Depending on speculation, Besson et al.34 provided an instructive suggestion their level, students could be asked to match catalyst types to by example of the selective oxidation of an hydroxyl group (see given catalytic converters (Figure 1). After Scheme 2 has been Scheme 4). explained, students should be able to calculate the atom utilization for the reaction of Scheme 3 and compare the two − processes. After they have been introduced to one of the Scheme 4. Speculative Mechanism for the Pt Bi Catalyzed fi Oxidation of Alcohols (adapted from ref 34) Figures 5 and 6, they could be asked to nd an interpretation for the remaining figure. On the basis of the information contained in Figure 7, students should be able to propose possible catalysts for other reactions of carbon monoxide. Examples for other reactions, including those of CO, are found elsewhere.38 ■ CONCLUSION Catalysis, and heterogeneous catalysis in particular, is a mature field of science. Catalysis grows and diversifies further as the world economy grows and diversifies. It contributes signifi- According to this proposal, dehydrogenation of the alcohol cantly to value creation in the real economy. From an to the aldehyde takes place on the noble metal surface. The environmental point of view, it impacts positively on the chemisorbed hydrogen reacts with a higher-oxidation-state viability of many human activities, not only those of a pure bismuth oxide species, giving water and a lower-oxidation-state chemical nature. To continue educating the catalysis experts of bismuth species. The lower-oxidation-state bismuth is re- tomorrow at schools and universities and to raise public oxidized by the oxidizing agent used for the overall reaction. awareness for the importance of catalysis is therefore of great The addition of bismuth keeps the platinum surface free of significance. To the lay person and to many undergraduate excess oxygen, thus preventing over oxidation of the substrate. students, catalysis appears as a rather complex field, not the The left part of the catalytic cycle exemplifies the action of a least because of the huge number of different catalytic materials common base-metal oxidation catalyst: bismuth switches and the many different catalytic processes that go with them. between two oxidation states and (in the case of Scheme 4) Often students are exposed to specific applications of catalysis oxidizes hydrogen to water. Depending on the substrate, Pt−Bi (e.g., descriptive heterogeneous catalysis) before they have catalysts allow for very high selectivities under mild reaction been exposed to the basic principles of the relevant surface conditions. Instead of air, hydrogen peroxide can also be used chemistry. This often contributes to the perception that as the oxidizing agent. Examples for the oxidation of catalysis is a “magic” art, rather than a science. Teaching hydroxymethylimidazoles to formylimidazoles are shown in important fundamentals of catalysis at an early stage can be Scheme 5.35,36 Formylimidazoles are important intermediates in expected to contribute to a deeper understanding. This, in turn, the synthesis of pharmaceuticals. Further examples for the will allow the student to put forthcoming information into successful application of Pt−Bi oxidation catalysts were perspective. In the paper at hand, an attempt was made to reported by Anderson et al.37 explain some important concepts of catalysis in a brief, but

1535 dx.doi.org/10.1021/ed200816g | J. Chem. Educ. 2012, 89, 1530−1536 Journal of Chemical Education Article understandable manner. Applications of industrial and general (28) Bond, G. C.; Louis, C.; Thompson, D. T. Catalysis by Gold; importance were used for demonstration purposes. Imperial College Press: London, 2006. (29) Campbell, I. M. Catalysis at Surfaces; Chapman and Hall: London, 1988; pp 132−142, 205−215. ■ AUTHOR INFORMATION (30) Gandhi, H. S.; Graham, G. W.; McCabe, R. W. J. Catal. 2003, Corresponding Author 216, 433−442. Twigg, M. V. Platinum Met. Rev. 2011, 55,43−53. * (31) Thomas, J. M.; Thomas, W. J. Principles and Practice of E-mail: [email protected]. Heterogeneous Catalysis; VCH: Weinheim, 1997; pp 576−590. Notes (32) Sharelynx Gold. http://www.sharelynx.com/gold/RareMetals. # fi php rhodium, accessed May 22, 2012. The author declares no competing nancial interest. (33) http://www.platinum.matthey.com./publications/pgm-market- reviews/archive/platinum-2009/Pt2009.html (Supply and Demand), ■ REFERENCES accessed Sept. 28, 2012. (34) Besson, M.; Lahmer, F.; Gallezot, P.; Fuertes, P.; Fleche,̀ G. J. (1) German Catalysis Society. Roadmap der deutschen Katalysefor- − ̈ ̈ Catal. 1995, 152, 116 121. schung; Katalyse, eine Schlusseltechnologie fur nachhaltiges Wirtschafts- (35) Bessard, Y.; Heveling, J. US Pat. US6’469’178, 2002. wachstum, 3rd ed.; Dechema: Frankfurt, 2010; p 3. (36) Heveling, J.; Wellig, A. Eur. Pat. EP916’659, 2002; Eur. Pat. (2) Behr, A. Angewandte Homogene Katalyse; Wiley-VCH: Weinheim, EP913’394, 2005. 2008; p 26. (English ed.: Behr, A.; Neubert, P. Applied Homogeneous (37) Anderson, R.; Griffin, K.; Johnston, P.; Alsters, P. L. Adv. Synth. Catalysis; Wiley-VCH: Weinheim, 2012.) − − Catal. 2003, 345, 517 523. (3) U.S. Climate Change Technology Program Technology (38) Wittcoff, H. A.; Reuben, B. G.; Plotkin, J. S. Industrial Organic Options for the Near and Long Term. http://www.climatetechnology. Chemicals, 2nd ed.; Wiley-Interscience: Hoboken, NJ, 2004. gov/library/2005/tech-options/tor2005-143.pdf, accessed May 16, 2012. (4) Henkel, K.-D. Ullmann’s Encyclopedia of Industrial Chemistry, 6th ed.; Wiley-VCH: Weinheim, 2003, Vol. 31; pp 125−157. (5) Grubbs, R. H. Tetrahedron 2004, 60, 7117−7140. (6) Heveling, J. J. Chem. Soc., Chem. Commun. 1987, 1152−1153. Heveling, J. J. Mol. Catal. 1990, 58,1−19. (7) Sheldon, R. A. Green Chem. 2007, 9, 1273−1283. (8) Trost, B. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 259−281. (9) Tschitschibabin, A. E. J. Prakt. Chem. 1924, 107, 122−128. (10) Ullmann’s Encyclopedia of Industrial Chemistry, 6th ed.; Wiley- VCH: Weinheim, 2003, Vol. 30; pp 481−484. (11) Heveling, J.; Armbruster, E.; Siegrist, W. Eur. Pat. EP691’955, 1997. (12) Heveling, J.; Armbruster, E.; Utiker, L.; Rohner, M.; Dettwiler, H.-R.; Chuck, R. J. Eur. Pat. EP770’687, 2002. (13) Atkins, P.; Overton, T.; Rourke, J.; Weller, M.; Armstrong, F. Shriver & Atkins’ Inorganic Chemistry, 5th ed.; Oxford University Press: Oxford, 2010; pp 690−721. (14) Sabatier, P.; Senderens, J. B. C. R. Acad. Sci. 1897, 124, 1358− 1361. (15) Ger. Pat. 141029, 1903 (to Leprince & Siveke). Normann, W. Brit. Pat. 1515, 1903. (16) Knothe, G. The AOCS Lipid Library, updated Jan. 6, 2010; http://lipidlibrary.aocs.org/history/Normann/index.htm (accessed Aug 2012). (17) Fiedler, M. Deutsche Gesellschaft für Fettwissenschaft, 2001; http://www.dgfett.de/history/normann/nr_fiedler.htm (accessed Aug 2012). (18) Horiuti, I.; Polanyi, M. Trans. Faraday Soc. 1934, 30, 1164− 1172. (19) Somorjai, G. A. J. Mol. Struct.: THEOCHEM 1998, 424, 101− 117. (20) Burwell, R. L., Jr. Acc. Chem. Res. 1969, 2, 289−296. (21) Sabatier, P.; Senderens, J. B. C. R. Acad. Sci. 1902, 134, 514− 516. (22) Rootsaert, W. J. M.; Sachtler, W. M. H. Z. Phys. Chem. 1960, 26, 16−26. (23) Schuit, G. C. A.; van Reijen, L. L. Adv. Catal. 1958, 10, 242− 317. (24) Bond, G. C. Platinum Met. Rev. 1968, 12, 100−105. Bond, G. C. Platinum Met. Rev. 1979, 23,46−53. (25) van Santen, R. A.; Neurock, M. Molecular Heterogeneous Catalysis; Wiley-VCH: Weinheim, 2006. (26) Tabor, C.; Narayanan, R.; El-Sayed, M. A. Model Systems in Catalysis; Rioux, R. M., Ed.; Springer: New York, 2010; pp 395−414. (27) Bond, G. C.; Sermon, P. A.; Webb, G.; Buchanan, D. A; Wells, P. B. J. Chem. Soc., Chem. Commun. 1973, 444−445.

1536 dx.doi.org/10.1021/ed200816g | J. Chem. Educ. 2012, 89, 1530−1536