Using a new type of nanoreactor, researchers at Chalmers University of Technology, Sweden, have mapped catalytic reactions on individual metallic nanoparticles. Their work could improve chemical processes, and lead to better Many technical processes, including chemical production, exhaust gas purification and the chemical storage of solar energy would not be possible without catalysts. In the chemical industry, the vast majority of products produced
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The urgency for finding clean energy sources is nowadays latent, and the role of hydrogen in the future of energy is well-recognized. However, there are still various barriers that limit the widespread utilization of hydrogen, which are mainly related to its storage and transportation. Chemical hydrogen storage stands out as a suitable alternative to traditional physical storage methods, and formic acid holds tremendous promise within the molecules studied so far.
This review summarizes some of the recent approaches considered in our research group for the preparation of efficient catalysts for the production of hydrogen via dehydrogenation of formic acid by using Pd-based heterogeneous catalysts supported on carbon or carbon-containing materials.
Several routes were considered to attain efficient catalysts, from the optimization of the size and composition of the nanoparticles to the modulation of important features of the support, such as the porous texture and nitrogen doping level. Energy consumption is closely linked to the world's development, population and living standards. CO 2 is a major greenhouse gas along with water vapor , and its emission to the atmosphere is responsible for changing the natural greenhouse effect that makes the Earth habitable.
The anthropogenic greenhouse effect is giving rise to catastrophic consequences, such as the increase in global temperatures, acidification of the oceans, melting arctic ice, decreased crop yield, human diseases and mortality, and so forth. The importance of non-fossil fuels, such as solar, biofuel, wind, geothermal heat, etc. The pivotal role of hydrogen in the future of energy is no longer questionable and, even though it is not naturally available as a ready-to-use molecule but is rather bound up in chemical compounds with other elements, its ideal status as an energy vector stems from its outstanding characteristics.
The principal advantages of hydrogen as an energy carrier can be summarized as follows Graetz, ; Rosen and Koohi-Fayegh, :. Nevertheless, safety issues related to its storage and transportation have limited its extensive utilization. However, despite the undesired properties of hydrogen in terms of safety, numerous studies revealed that the danger of hydrogen might not be worse than that shown by other fuels.
Still, from a practical standpoint, storing, and transporting a hydrogen storage molecule that can provide hydrogen when required would be a better option than storing and transporting hydrogen in tanks for pressurized hydrogen gas or liquid hydrogen, which require high-pressure systems or high liquefaction energy. The search for solid and liquid-state hydrogen storage materials has been the focus of fruitful investigations in the last decades.
However, the practical application of some of these hydrogen storage molecules is greatly limited due to their low kinetics for reversible H 2 adsorption-desorption reactions, thermodynamic stability, low inherent thermal conductivity, high price, and toxicity Czaun et al.
Formic acid is currently considered one of the most promising candidates. It was identified as a potential hydrogen storage medium 40 years ago Williams et al.
Furthermore, it is in liquid phase at ambient temperature, which makes its transportation and refueling easy so that its handling could be comparable to that of diesel and gasoline Enthaler et al. It is well-known that formic acid decomposition can take place by dehydration decarbonylation and dehydrogenation decarboxylation , which are represented by the following chemical equations Eppinger and Huang, :. Formic acid dehydration can be avoided through highly selective catalysts able to boost its dehydrogenation to generate H 2 and CO 2.
It has been reported that the pathway followed in the decomposition of formic acid by either dehydration or dehydrogenation is strongly dependent on the catalytic surface, which controls the adsorption of formic acid molecules. It was claimed that large terrace sites tend to adsorb the molecules of formic acid following a bidentate form, which gives raise to the dehydrogenation pathway, while surface-unsaturated sites boost the dehydration pathway Tedsree et al.
Besides its intrinsic features, another important aspect of the use of formic acid as a hydrogen storage material is that the CO 2 generated in formic acid dehydrogenation can be subsequently hydrogenated so that formic acid molecules are regenerated in a carbon-free emission process Fellay et al. Figure 1. Carbon-neutral energy storage using formic acid as a hydrogen carrier molecule. Williams first reported on the electrochemical reduction of CO 2 to formic acid in Williams et al.
However, despite the ideality of this system, several aspects should be considered to boost the thermodynamically uphill formation of liquid formic acid from gaseous CO 2 and H 2. Since Coffey first reported the decomposition of formic acid over a homogeneous catalytic system in Coffey, , many investigations dealing with the preparation of highly active and robust homogeneous catalysts that selectively produce H 2 and CO 2 from formic acid under mild conditions have been documented Fukuzumi et al.
However, achieving competitive and selective heterogeneous catalysts under mild conditions is still a difficult task Enthaler et al. The investigation of the decomposition of formic acid over heterogeneous catalysts dates back to the s, but in the initial studies the optimization of the catalysts, as well as the measurement of the CO evolved from the formic acid dehydration side reaction, were not deeply considered Grasemann and Laurenczy, Then, the development of heterogeneous catalysts for formic acid dehydrogenation in liquid-phase is highly desirable Zhu and Xu, The search for an optimum heterogeneous catalyst encompasses the investigation of several active phases, mainly in the form of noble metal nanoparticles, but reports in which non-noble metal nanoparticles are studied can be also found in the literature, approaching this issue from both experimental and theoretical perspectives Yoo et al.
Among all the catalysts studied in this application, those based on palladium have been claimed to be very promising alternatives, and they have received great attention not only because they are more tolerant to CO than other metals, but also because relatively high hydrogen conversion and selectivity values have been achieved under moderate temperatures He and Li, Among them, carbon materials are certainly the most extensively investigated so far.
Among those features, their resistance to basic and acid media, tailored porous structure, controllable hydrophilicity, and the possibility of incorporation of heteroatoms in their structure are of particular interest for the formic acid dehydrogenation reaction. Carbon materials are ideal catalytic support for the present application, not only because they serve as anchoring sites for the metal nanoparticles but also because they can be modified so as to incorporate basic functionalities that can be actively involved in the formic acid dehydrogenation reaction, ultimately resulting in highly performing catalysts.
In order to provide a wide view of the recent breakthroughs achieved by using catalysts based on carbon materials, some representative examples are listed in Table 1. Table 1. Representative catalysts based on carbon materials used in the formic acid dehydrogenation reaction. In this review, we address some of the recent studies conducted by our research group toward the design of Pd-based heterogeneous catalysts supported on carbon or carbon-containing materials for the formic acid dehydrogenation reaction in liquid phase.
As it was previously mentioned, Pd-based catalysts have been claimed to be the most active toward hydrogen production from the formic acid dehydrogenation reaction. Numerous factors, such as morphology of the metallic active phase, composition and architecture of the nanoparticles, metal loading, etc. Most of the investigated heterogeneous catalysts studied in this application are carbon-supported systems.
However, interesting reports on several kinds of carbon materials and carbon-based materials, such as reduced graphene oxide rGO Ping et al. Herein some of the recent investigations performed in our research group will be summarized. The effect of the features of both metal active phase and carbon-based supports on the catalytic performance in the formic acid dehydrogenation reaction were studied in the investigations herein reviewed.
The investigation of the active phase properties in the final catalytic performance is usually the cornerstone of the successful preparation of highly-performing catalysts.
Numerous aspects such as nanoparticle size, shape, and electronic features have already been studied by those researchers tackling the design of catalysts for hydrogen production from the decomposition of formic acid. The synthesis of colloidal size-controlled Pd nanoparticles was based on a polyol process by using palladium II acetate as a Pd precursor, polyvinylpyrrolidone PVP as a stabilizing agent and ethylene glycol as the solvent and reducing agent.
The as-synthetized colloidal nanoparticles were subsequently loaded on the carbon support and catalysts with an average nanoparticles size ranging from 2.
All catalysts were thoroughly characterized and the presence of Pd 0 in the nanoparticles was confirmed by X-ray photoelectron XPS and X-ray absorption fine structure XAFS spectroscopies. The results of the hydrogen produced after 3 h of reaction as a function of the size of the nanoparticles are summarized in Figure 2A. The volcano type relationship found between the hydrogen production ability and the size of the nanoparticles in that study was ascribed to the relative proportion of low-coordinated atoms LC and high-coordinated atoms HC with respect to the total number of surface atoms present in the catalysts.
To get further insight into the size-sensitivity observed, we assumed that Pd nanoparticles were cuboctahedral in shape, with a cubic close-packed structure in this size range and the full-shell nanoparticles model was adopted to calculate geometric parameters Mori et al. If all the atoms on the nanoparticle surface possess the same catalytic activity toward the hydrogen production, the TOF values calculated on the basis of the surface atoms should be the same regardless of the Pd particle sizes.
Such differences in the normalized TOF values indicated that all the Pd surface sites did not present the same catalytic activity in the formic acid decomposition. Figure 2. Copyright Wiley. Furthermore, a plausible mechanism pathway was proposed Figure 3.
Figure 3. In addition, to get more information about the size sensitivity in the elementary steps of the formic acid dehydrogenation, Kinetic Isotope Effect KIE experiments were conducted by monitoring the evolution of the reaction using deuterated formic acid HCOOD and DCOOH and the results for each catalyst are listed in Table 2. Subsequent studies also tackled the investigation of the size sensitivity. For instance, Zhang S. It was also observed that the catalytic performance displayed a volcano-type relationship with the Pd nanoparticle size, with the sample containing an average size of 2.
Li and co-workers Li J. In that case, sodium citrate was used as a stabilizer and several Pd precursors to sodium citrate ratios were used so as to obtain Pd nanoparticles with average sizes ranging from 2. Under the experimental conditions used in that study, the smallest nanoparticles displayed the best performance among those investigated, which was related to a better dispersion of the nanoparticles and larger proportion of positively charged Pd species. Jin et al. The control of the nanoparticle size was achieved by means of modifying experimental conditions such as Pd precursor [i.
In that case, the catalysts synthesized from palladium nitrate displayed the smallest NP size and, in turn, showed the best performance in the formic acid dehydrogenation reaction. As was previously mentioned, most of the heterogeneous catalysts used in the formic acid dehydrogenation reaction are based on Pd nanoparticles.
However, Pd monometallic systems often suffer from deactivation caused by the adsorption of reaction intermediates on the surface of the nanoparticles. It was observed that the use of bimetallic or multimetallic systems can greatly palliate such problem and display better performance than the Pd monometallic counterpart.
Such enhancement of the catalytic activity and selectivity of the bimetallic and multimetallic systems are usually ascribed to the modification of the Pd electronic density and geometric structure as well as resistance to poisoning intermediates Zhang et al. Furthermore, the utilization of bimetallic or multimetallic systems has been a widely employed strategy to reduce the cost of the final catalysts, particularly when non-noble metals are used in their compositions.
A number of bimetallic and multimetallic heterogeneous catalysts, such as PdNi Qin Y. Among them, noble metal-based systems have been so far the most studied, and PdAg-based catalysts have taken pole position in attracting extensive investigations Mori et al.
Their superior performance is usually ascribed to the efficient charge transfer from Ag to Pd that results in electronically promoted Pd species, which are more active in catalyzing the formic acid dehydrogenation reaction.
Since Tedsree et al. Unlike monometallic catalysts, factors such as composition and configuration of the nanoparticles should be kept in mind while evaluating the performance of bimetallic or multimetallic catalysts.
The complexity of these systems usually complicates the proper evaluation of only one aspect such as the composition or size of the bimetallic nanoparticles. From these composition-controlled colloids, 12 carbon-supported catalysts were prepared. Figure 4. Copyright American Chemical Society. Once the best-performing catalyst was identified, its applicability in a large-scale reactor was also checked by using a burette system equipped with a reflux condenser, so that the hydrogen generation could be measured by observing the volume of gas displaced.
As for the effect of PVP, it was seen that the catalytic performance decayed as the capping agent content increased, which was initially ascribed to either change in the surface composition of the nanoparticles and electronic effect exerted by the PVP molecules, or changes in the size of the nanoparticles. In order to ascertain the relationship between the composition of the nanoparticles and their activity, the catalysts were thoroughly characterized.
Furthermore, it was shown that the addition of Ag in the nanoparticles resulted in smaller nanoparticles as compared to the Pd monometallic counterpart catalysts. That fact was related to the favored reduction of Pd ions when Ag ions were present, which would lead to a larger number of seeds in the nucleation step and would eventually produce nanoparticles with a smaller size. Table 3. In the case of the catalysts, those peaks were shifted as compared to the references, confirming the presence of heteroatomic Pd-Ag bonding in the nanoparticles.
Figure 5. The electronic structure of these catalysts was also analyzed by means of XPS and, even though both Pd and Ag were mainly in their metallic form, oxidized forms were also detected. Furthermore, the charge transfer from Ag to Pd was also considered. It was observed that such charge transfer was hampered for high PVP content in the nanoparticles, which was due to its capping effect on the Ag species. In view of the characterization results, the catalytic tendency displayed by the set of samples were discussed.
First, it was claimed that the poor performance displayed by the Pd1Ag4 set of catalysts could be due to the aggregation found in those samples. However, that aspect did not determine the tendency observed for the other three sets of catalysts Pd1Ag0.
Farrauto , Lucas Dorazio , C. Particularly useful are the succinct summaries throughout the book Introduction to Catalysis and Industrial Catalytic Processes. Robert J. Introduces major catalytic processes including products from the petroleum, chemical, environmental and alternative energy industries Provides an easy to read description of the fundamentals of catalysis and some of the major catalytic industrial processes used today Offers a rationale for process designs based on kinetics and thermodynamics Alternative energy topics include the hydrogen economy, fuels cells, bio catalytic enzymes production of ethanol fuel from corn and biodiesel from vegetable oils Problem sets of included with answers available to faculty who use the book Review: "In less than pages, it serves as an excellent introduction to these subjects whether for advanced students or those seeking to learn more about these subjects on their own time He has over 40 years industrial experience in catalysis and has commercialized a number of technologies in the environmental, chemical and alternative energy fields.
Catalysis in Industry
Europe is a leading player in both academic research on catalysis as well in the industrial implementation of catalysts, but this leadership is being increasingly impaired by steeply growing economies such as China, or mature but still innovating economies such as US or Japan. The European leadership in catalysis is progressively eroded from the still present fragmentation, the insufficient coordination between European and country-based activities, the sometime dramatic decrease of funds for fundamental research in many European countries, the lack of large-scale infrastructures dedicated to catalysis. The key actions to be undertaken at European level in the next ten years in the field of catalysis are:. The European strategy in this field is longsighted and comprehensive, and many of the strategic initiatives undertaken by the European Commission are closely intertwined with catalysis. In this regard it is worth to mention, inter alia :. Nevertheless, weaknesses affecting the action of Europe in this strategic field are:. To address these and further strategic challenges for Europe, the European Commission NMP Research Programme has launched several thematic clusters bringing together EU funded projects and other stakeholders.
TWC Three-way Catalysts
Once considered a waste product, carbon now is the foundation of a vibrant new U. Strides in catalysis research have equipped U. PNNL is on the leading edge of innovation in the development of new chemistries and materials that could open pathways to new energy storage technologies and the development of fuels derived from cheap and abundant domestic resources. Our research focuses on attaining a deeper understanding of chemical catalysts. Catalysts are substances that can control chemical reactions without being consumed by them. Our goal is to open the door to a new generation of cleaner, more resilient, and more cost-effective energy resources using carbon and other waste products as raw materials.SEE VIDEO BY TOPIC: Yongdan Li: “Industrial catalysis looks to the future”
China E-mail: ylguo ecust. Smarsly phys. The article was received on 29 Jan , accepted on 27 Mar and first published on 28 Mar If you are not the author of this article and you wish to reproduce material from it in a third party non-RSC publication you must formally request permission using Copyright Clearance Center. Go to our Instructions for using Copyright Clearance Center page for details. Authors contributing to RSC publications journal articles, books or book chapters do not need to formally request permission to reproduce material contained in this article provided that the correct acknowledgement is given with the reproduced material. If the material has been adapted instead of reproduced from the original RSC publication "Reproduced from" can be substituted with "Adapted from". In all cases the Ref.
Catalysts in 21st Century Energy
The urgency for finding clean energy sources is nowadays latent, and the role of hydrogen in the future of energy is well-recognized. However, there are still various barriers that limit the widespread utilization of hydrogen, which are mainly related to its storage and transportation. Chemical hydrogen storage stands out as a suitable alternative to traditional physical storage methods, and formic acid holds tremendous promise within the molecules studied so far. This review summarizes some of the recent approaches considered in our research group for the preparation of efficient catalysts for the production of hydrogen via dehydrogenation of formic acid by using Pd-based heterogeneous catalysts supported on carbon or carbon-containing materials.
Selective hydrogen transfer remains a central research focus in catalysis: hydrogenation and dehydrogenation have central roles, both historical and contemporary, in all aspects of fuel, agricultural, pharmaceutical, and fine chemical synthesis. Our lab has been involved in this area by designing homogeneous catalysts for dehydrogenation and hydrogen transfer that fill needs ranging from on-demand hydrogen storage to fine chemical synthesis. A keen eye toward mechanism has enabled us to develop systems with excellent selectivity and longevity and demonstrate these in a diversity of high-value applications. Here we describe recent work from our lab in these areas that are linked by a central mechanistic trichotomy of catalyst initiation pathways that lead highly analogous precursors to a diversity of useful applications. The article was received on 26 Apr , accepted on 04 Jun and first published on 04 Jun If you are not the author of this article and you wish to reproduce material from it in a third party non-RSC publication you must formally request permission using Copyright Clearance Center. Go to our Instructions for using Copyright Clearance Center page for details. Authors contributing to RSC publications journal articles, books or book chapters do not need to formally request permission to reproduce material contained in this article provided that the correct acknowledgement is given with the reproduced material. If the material has been adapted instead of reproduced from the original RSC publication "Reproduced from" can be substituted with "Adapted from". In all cases the Ref.
A catalytic converter is an exhaust emission control device that reduces toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction an oxidation and a reduction reaction. Catalytic converters are usually used with internal combustion engines fueled by either gasoline or diesel —including lean-burn engines as well as kerosene heaters and stoves. The first widespread introduction of catalytic converters was in the United States automobile market. To comply with the U. Environmental Protection Agency 's stricter regulation of exhaust emissions, most gasoline-powered vehicles starting with the model year must be equipped with catalytic converters. In , two-way catalytic converters were rendered obsolete by "three-way" converters that also reduce oxides of nitrogen NO x ;  however, two-way converters are still used for lean-burn engines. This is because three-way-converters require either rich or stoichiometric combustion to successfully reduce NO x. Although catalytic converters are most commonly applied to exhaust systems in automobiles, they are also used on electrical generators , forklifts , mining equipment, trucks , buses , locomotives , and motorcycles. They are also used on some wood stoves to control emissions.
Iridium-Based Hydride Transfer Catalysts: from Hydrogen Storage to Fine Chemicals
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Catalyst Bins & Containers
Researchers at the Department of Energy's SLAC National Accelerator Laboratory and Stanford University have shown for the first time that a cheap catalyst can split water and generate hydrogen gas for hours on end in the harsh environment of a commercial device. The electrolyzer technology, which is based on a polymer electrolyte membrane PEM , has potential for large-scale hydrogen production powered by renewable energy, but it has been held back in part by the high cost of the precious metal catalysts, like platinum and iridium, needed to boost the efficiency of the chemical reactions.
Cheaper catalyst can generate hydrogen in a commercial device
Bartholomew , Robert J. In this book the authors, present the definitive account of industrial catalytic processes. Throughout Fundamentals of Industrial Catalytic Processes the information is illustrated with many case studies and problems.
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Catalysis in Industry is a peer reviewed journal. We use a single blind peer review format. The average period from submission to first decision in was 30 days, and that from first decision to acceptance was 25 days.