Leibniz‐Institute for Catalysis (LIKAT): From Basic Research to Practical Applications

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTCombination Catalysts Consisting of a Homogeneous Catalyst Tethered to a Silica-Supported Palladium Heterogeneous Catalyst: Arene HydrogenationHanrong Gao and Robert J. AngeliciView Author Information Department of Chemistry and Ames Laboratory Iowa State University, Ames, Iowa 50011 Cite this: J. Am. Chem. Soc. 1997, 119, 29, 6937–6938Publication Date (Web):July 23, 1997Publication History Received31 March 1997Published online23 July 1997Published inissue 1 July 1997https://pubs.acs.org/doi/10.1021/ja9710058https://doi.org/10.1021/ja9710058rapid-communicationACS PublicationsCopyright © 1997 American Chemical SocietyRequest reuse permissionsArticle Views1298Altmetric-Citations71LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Aromatic compounds,Catalysts,Hydrocarbons,Hydrogenation,Metals Get e-Alerts

Lactic acid (2-hydroxypropionic acid, CH3CHOHCOOH) is one of the platform chemicals derived from biomass. It is used in the food industry and in the manufacture of biodegradable plastics and useful chemicals. Recently, various examinations were carried out not only by fermentation but also by the chemical methods using heterogeneous and homogenous catalysts. This chapter focuses on the chemical processes with heterogeneous catalysts in lactic acid and lactate ester productions from sugars. Bronsted basic catalysts and Lewis acid catalysts gave lactic acid in high yields. In the lactic acid productions from triose, lactic acid ester is obtained with high yields of nearly 100 % in alcohols around 100 °C using Sn-β zeolite, Sn–carbon–silica, and H-USY catalysts. In the lactic acid production from hexose, lactic acid ester or a lactate salts was obtained from glucose, fructose, and sucrose with the comparatively high selectivity of about 50 % by several catalytic processes, that were in water around 50 °C using heterogeneous basic catalysts, such as activated hydrotalcite catalyst, in hydrothermal water around 300 °C using homogeneous basic catalysts, such as NaOH and ZnSO4, and in alcohols around 160 °C using heterogeneous Lewis acid catalysts, such as Sn-β zeolite.

Liquid fuel synthesis via CO2 hydrogenation by coupling homogeneous and heterogeneous catalysis

The importance of catalysis in chemistry has not to be proved anymore. Be it homogeneous or heterogeneous catalysis, the constant progresses observed in that field proves its obvious interest. The asymmetric homogeneous catalysis is a method of choice to synthesize chiral substances. Indeed, it allows the obtention of these compounds in an enantioselective way. During transition metal mediated catalytic asymmetric reactions, the chirality is induced by the presence of organic monodentate or bidentate chiral ligand, directly linked to the metal. Very good results were obtained in this kind of reaction with chiral ligands based on binaphthyl skeleton. Initially, this thesis work consisted in the study of the double [1,2] Wittig rearrangement of binaphthyl ethers. It was shown, for allyl carbanion, that only one diastereoisomer is formed during the rearrangement among the three possible one. This diastereoisomer has a C2 symmetry axis and the absolute configuration of the two new asymmetric centers created was assigned. On the other hand, for benzyl or benzhydril carbanions, the results are differents. For the former, the three possible diastereisomer are formed with the unsymmetrical one as the major compound. In the latter case, no rearrangement takes place and only starting material is recovered after neutralization of the reaction mixture. Then, the potential of double [1,2] Wittig rearrangements applied to allyl binaphthyl ethers was evaluate in order to synthesize homochiral compounds usable in asymmetric homogeneous catalysis. It was shown that this transformation could be used to give access to the enantiopur acid 1,1'-binaphtyl-2,2'-dicarboxylic which finds applications in the field of the asymmetric catalysis. The high diastereoselectivity observed during this double rearrangement allowed to develop the kinetic resolution of the binaphthyl skeleton by means of the asymmetric epoxidation according to the conditions described by K.B Sharpless and T Katsuki. Finally, taking profit of the high diastereoselectivity already mentioned, it was possible to elaborate out a new phosphorus ligand whose stereoinduction capacity was evaluated for catalytic asymmetric hydrosilylation.

Most of the chemical reactions used to produce the molecules and materials that our societies need—for example, in the petrochemical and pharmaceutical industries, the synthesis of plastics and other materials, and the production of foods and drinks—make use of catalysts. These speed up the rate at which atoms and molecules rearrange themselves into new forms, and provide a degree of control over the shape and form of those rearrangements. Catalysts let us drive a chemical reaction in a selected direction, in preference to others that could occur. In this way they turn chemistry from crude cookery into a rational and precise form of molecular engineering. And always we can draw inspiration, and sometimes borrow tricks, from the delicate and precise catalytic processes that occur in nature, where enzymes carry out processes in aqueous solution and at mild temperatures and pressures that often we struggle to achieve with far more extreme conditions—such as the fixation of atmospheric nitrogen into useful forms. It is often claimed that this particular catalytic process—the Haber–Bosch process for converting nitrogen into ammonia, discovered just over a century ago—has, by making possible the synthesis of artificial fertilizers, had a greater effect on humankind than any other single chemical innovation. It is what allows us to feed the world. Yet while nature performs this reaction using soluble molecules (enzymes) as catalysts, the Haber–Bosch process uses powdered iron (plus some additives). The reactions between nitrogen and hydrogen take place on the surface of iron particles: this is so-called heterogeneous catalysis, involving surface chemistry, rather than the homogeneous catalysis of enzyme reactions, in which the catalysts are soluble molecules. Both homogeneous and heterogeneous catalysis are essential to the chemical industries. National Science Review spoke with two of the foremost practitioners of the latter field—Nobel laureate Gerhard Ertl of the Fritz Haber Institute in Berlin, Germany, and Avelino Corma of the Institute of Chemical Technology (ITQ) at the Polytechnic University of Valencia, Spain—about the current status of research in catalysis and prospects for the future.

The effective transesterification process to produce fatty acid methyl esters (FAME) requires the use of low-cost, less corrosive, environmentally friendly and effective catalysts. Currently, worldwide biodiesel production revolves around the use of alkaline and acidic catalysts employed in heterogeneous and homogeneous phases. Homogeneous catalysts (soluble catalysts) for FAME production have been widespread for a while, but solid catalysts (heterogeneous catalysts) are a newer development for FAME production. The rate of reaction is much increased when homogeneous basic catalysts are used, but the main drawback is the cost of the process which arises due to the separation of catalysts from the reaction media after product formation. A promising field for catalytic biodiesel production is the use of heteropoly acids (HPAs) and polyoxometalate compounds. The flexibility of their structures and super acidic properties can be enhanced by incorporation of polyoxometalate anions into the complex proton acids. This pseudo liquid phase makes it possible for nearly all mobile protons to take part in the catalysis process. Carbonaceous materials which are obtained after sulfonation show promising catalytic activity towards the transesterification process. Another promising heterogeneous acid catalyst used for FAME production is vanadium phosphate. Furthermore, biocatalysts are receiving attention for large-scale FAME production in which lipase is the most common one used successfully This review critically describes the most important homogeneous and heterogeneous catalysts used in the current FAME production, with future directions for their use.

Organometallic cluster compounds with metal frameworks containing more than three metal atoms are akin to metal particles and stepped metal surfaces having neibouring multimetallic centers. These metal centers are chemically accomodated by appropriate ligand molecules such as carbonyls, phosphines, aryls and olefins. The similarity between very small metal particles and molecular clusters was firsly proposed by Muetterties(1) and Chini(2) on the basis of the chemical behavior of lignads such as CO coordinated to a cluster framework and chemisorption onto the metal surface. The adjacent metal sites in polynuclear metal clusters make available multi-metallic coordination environments(e.g., face, edge and kink) that can not be realized at a single metal atom or ionic site typical of most homogeneous metal complex catalysts. Transition metal cluster complexes are ideal objects for the study of collective behavior in stoichiometric and catalytic reactions. In this sense, metal clusters occupy an intermediate position between molecular metal complexes(homogeneous catalysts) and bulky metals such as films and crystals (classic heterogeneous catalysts) in catalysis. Heterogeneous catalysts which involve colloidal, crystalline, and supported metal particles have the advantage of being readily separable from the products, which gives a practical advantage over homogeneous metal complex catalysts even with a high selectivity and uniformity. Catalytically active metal/alloy particles of several nanometer(nm) diameters are usually dispersed on supporting materials such as metal oxides, sulfides or carbon having large surface area to prevent further metal agglomeration (“sintering”). Several examples of supported multi-metal catalysts used in industrial proccesses are Fe/K-Al2O3 for ammonia synthesis, Cu/ZnO for methanol synthesis, Ag/Re-Al2O3 for selective epoxidation of ethylene, and Pt/Re(or Ru/Cu)Al2O3 which is used for naphtha reforming. The activity and selectivity of supported metal catalysts generally depend on the state of metal dispersion(ensemble sizes), structure(shape and morphology), metal composition(geometric distribution of multi metals), and metal-support(metal-oxide/sulfide) interactions.

Metal-based catalysts, encompassing both homogeneous and heterogeneous types, play a vital role in the modern chemical industry. Heterogeneous metal-based catalysts usually possess more varied catalytically active centers than homogeneous catalysts, making it challenging to regulate their catalytic performance. In contrast, homogeneous catalysts have defined active-site structures, and their performance can be easily adjusted by modifying the ligand. These characteristics lead to remarkable conceptual and technical differences between homogeneous and heterogeneous catalysts. As a recently emerging class of catalytic material, single-atom catalysts (SACs) have become one of the most active new frontiers in the catalysis field and show great potential to bridge homogeneous and heterogeneous catalytic processes. This review documents a brief introduction to SACs and their role in a range of reactions involving single-atom catalysis. To fully understand process-structure-property relationships of single-atom catalysis in chemical reactions, active sites or coordination structure and performance regulation strategies (e.g., tuning chemical and physical environment of single atoms) of SACs are comprehensively summarized. Furthermore, we discuss the application limitations, development trends and future challenges of single-atom catalysis and present a perspective on further constructing a highly efficient (e.g., activity, selectivity and stability), single-atom catalytic system for a broader scope of reactions.

Summary To keep up with the fast-paced transitioning of the global energy sector, which is constantly thriving to enable reliable, economic, and sustainable energy production, catalysis research has been required to continuously evolve in response. The challenges in the existing systems are predominantly due to dependencies on heterogeneous solid catalysts that are susceptible to coking. In this respect, liquid-metal (LM) catalysts have been demonstrated to have a critical advantage over conventional catalysts. Recently, LMs acquired a place in catalysis, with a reputation often synonymous with interesting properties and a remarkable ability to break trade-offs between homogeneous and heterogeneous catalysis. This review bridges the fundamental principles of LM research and the recent advances in LM-based thermal and electrochemical catalysis for energy applications. Moreover, emerging approaches for the improved utilization of LMs are outlined, and the concepts requiring greater research attention that could enable the development of exciting energy solutions are highlighted.

A BRIEF OVERVIEW ON SINGLE-ATOM CATALYSIS: CONCEPTS AND APPLICATIONS. Catalytic processes became extremely important for the development of our society, especially after the second industrial revolution. Thus, the research for more efficient catalysts is an obstacle to overcome to achieve cheaper processes, higher yields, and selectivity of desired products. In this context, single-atom catalysis emerges as a promising alternative to unite the advantages of traditional homogeneous and heterogeneous catalysis. Catalysis by single-atoms is a bridge that unites in a single catalyst the ease of recovery and reuse (from heterogeneous catalysis) with the high exposure and uniformity of sites (from homogeneous catalysis). Thus, single-atom catalysts (SACs) and single-atom alloys (SAAs) have already found several applications in the literature, such as in hydrogenation, oxidation, conversion of biomass derivatives, electrocatalysis, and photocatalysis. However, it is essential to emphasize that it is still a field that is expanding and relatively new, with several opportunities and many barriers to surpass. In this review, concepts of homogeneous, enzymatic, and heterogeneous catalysis will be addressed, as well as fundamental aspects of single-atom catalysis, preparation methods, characterization, and current challenges.

Application of heterogeneous catalysts in olefin hydroformylation

The selective hydrogenation of alkynes to their corresponding alkenes is an important type of organic transformation, which is currently accomplished by modified palladium catalysts. Herein, we rep...

Catalysis by soluble complexes of transition metals is a rapidly gaining mode of catalysis in organic synthesis. These metals form bonds with one or more carbons in an organic reactant resulting in complexes that are known as organometallic complexes. Catalysis by these complexes is often referred to as homogeneous catalysis. Among the important applications of homogeneous catalysis in organic synthesis are isomerization of olefins; hydrogenation of olefins (carried out using Wilkinson type catalysts); oligomerization; hydroformylation of olefins to aldehydes with CO and H2 (the oxo process); carbonylation of unsaturated hydrocarbons and alcohols with CO (and coreactants such as water); oxidation of olefins to aldehydes, ketones, and alkenyl esters (Wacker process); and metathesis of olefins (a novel kind of disproportionation). Enantioselective catalysis that rivals enzymes in selectivity is a major development in homogeneous catalysis. As a result, many earlier processes in the pharmaceutical and perfumery industries are being replaced by more elegant syntheses using soluble catalysts in which “handedness” is introduced in the critical step of the process, thus avoiding the costly separation of racemic mixtures. In view of its importance in organic synthesis, enantioselective (or asymmetric) catalysis was briefly introduced in Chapter 6 and is again considered as a powerful synthetic tool in Chapter 9. This chapter is concerned with the use in general of homogeneous catalysis in organic synthesis (including asymmetric synthesis). Among the several books and reviews written on the subject, the following may be mentioned: Halpern (1975, 1982), Bau et al. (1978), Parshall (1980), Masters (1981), Collman and Hegedus (1980), Eby and Singleton (1983), Chaudhari (1984), Davidson (1984), Kegley and Pinhas (1986), Collman et al. (1987), Parshall and Nugent (1988), Noyori and Kitamura (1989), Parshall and Ittel (1992), Gates (1992), Chan (1993), Akutagawa (1995). Gas (or liquid)-phase reactions on solid catalysts are among the most common industrial reactions. However, homogeneous catalysis is rapidly catching up. Excluding applications in petroleum refining, the dollar value of organic chemicals produced worldwide by homogeneous catalysis (more than $35 billion) is quite impressive compared to that by heterogeneous catalysis (more than $45 billion). Attempts are now under way to find an integrated approach to homogeneous and heterogeneous catalyses (Moulijn et al., 1993).

"… Despite the introduction of high-throughput and combinatorial methods that certainly can be useful in the process of catalysts optimization, it is recognized that the generation of fundamental knowledge at the molecular level is key for the development of new concepts and for reaching the final objective of solid catalysts by design …" Read more in the Editorial by Avelino Corma.

Homogeneous base catalyst has wide acceptability in biodiesel production because of their fast reaction rates. However, postproduction costs incurred from aqueous quenching, wastewater and loss of catalysts led to the search for alternatives. Heterogeneous base catalyst is developed to cater these problems. The advantages of heterogeneous catalyst are their high basicity and non-toxicity. This work compared the production of biodiesel using two different kind of catalysts that is homogeneous catalyst (sodium hydroxide, NaOH and potassium hydroxide, KOH) and heterogeneous catalysts (calcium, oxide, CaO catalyst derived from chicken and ostrich eggshells). Transesterification of waste cooking oil (WCO) and methanol in the presence of heterogeneous base catalyst was conducted at an optimal reaction condition (calcination temperature for catalyst: 1000 °C; catalyst loading amount: 1.5 wt%; methanol/oil molar ratio: 10:1; reaction temperature: 65 °C; reaction time: 2 hours) with 97% biodiesel yield was obtained. While, the homogeneous base catalyst gave higher biodiesel yield of 98% at optimum operating condition (catalyst concentration: 0.75 wt%; methanol/oil molar ratio: 6:1; reaction temperature: 65 °C; reaction time: 1 hours). The slight difference in the biodiesel yield was due to the stronger basic strength in the homogeneous catalyst and were not statistically not different (p=0.05). However, despite these advances, the ultimate aim of producing biodiesel at affordable low cost and minimal-environmental-impact is yet to be realized.