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MATHEMATICS (656 journals)                  1 2 3 4 | Last

Showing 1 - 200 of 538 Journals sorted alphabetically
Abakós     Open Access   (Followers: 4)
Abhandlungen aus dem Mathematischen Seminar der Universitat Hamburg     Hybrid Journal   (Followers: 3)
Academic Voices : A Multidisciplinary Journal     Open Access   (Followers: 2)
Accounting Perspectives     Full-text available via subscription   (Followers: 8)
ACM Transactions on Algorithms (TALG)     Hybrid Journal   (Followers: 16)
ACM Transactions on Computational Logic (TOCL)     Hybrid Journal   (Followers: 4)
ACM Transactions on Mathematical Software (TOMS)     Hybrid Journal   (Followers: 6)
ACS Applied Materials & Interfaces     Full-text available via subscription   (Followers: 22)
Acta Applicandae Mathematicae     Hybrid Journal   (Followers: 1)
Acta Mathematica     Hybrid Journal   (Followers: 11)
Acta Mathematica Hungarica     Hybrid Journal   (Followers: 2)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5)
Acta Mathematica Sinica, English Series     Hybrid Journal   (Followers: 5)
Acta Mathematica Vietnamica     Hybrid Journal  
Acta Mathematicae Applicatae Sinica, English Series     Hybrid Journal  
Advanced Science Letters     Full-text available via subscription   (Followers: 8)
Advances in Applied Clifford Algebras     Hybrid Journal   (Followers: 3)
Advances in Calculus of Variations     Hybrid Journal   (Followers: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5)
Advances in Complex Systems     Hybrid Journal   (Followers: 7)
Advances in Computational Mathematics     Hybrid Journal   (Followers: 15)
Advances in Decision Sciences     Open Access   (Followers: 5)
Advances in Difference Equations     Open Access   (Followers: 1)
Advances in Fixed Point Theory     Open Access   (Followers: 5)
Advances in Geosciences (ADGEO)     Open Access   (Followers: 10)
Advances in Linear Algebra & Matrix Theory     Open Access   (Followers: 2)
Advances in Materials Sciences     Open Access   (Followers: 16)
Advances in Mathematical Physics     Open Access   (Followers: 5)
Advances in Mathematics     Full-text available via subscription   (Followers: 10)
Advances in Numerical Analysis     Open Access   (Followers: 4)
Advances in Operations Research     Open Access   (Followers: 11)
Advances in Porous Media     Full-text available via subscription   (Followers: 4)
Advances in Pure and Applied Mathematics     Hybrid Journal   (Followers: 6)
Advances in Pure Mathematics     Open Access   (Followers: 4)
Advances in Science and Research (ASR)     Open Access   (Followers: 6)
Aequationes Mathematicae     Hybrid Journal   (Followers: 2)
African Journal of Educational Studies in Mathematics and Sciences     Full-text available via subscription   (Followers: 5)
African Journal of Mathematics and Computer Science Research     Open Access   (Followers: 4)
Afrika Matematika     Hybrid Journal   (Followers: 1)
Air, Soil & Water Research     Open Access   (Followers: 8)
AKSIOMA Journal of Mathematics Education     Open Access   (Followers: 1)
Al-Jabar : Jurnal Pendidikan Matematika     Open Access  
Algebra and Logic     Hybrid Journal   (Followers: 4)
Algebra Colloquium     Hybrid Journal   (Followers: 4)
Algebra Universalis     Hybrid Journal   (Followers: 2)
Algorithmic Operations Research     Full-text available via subscription   (Followers: 5)
Algorithms     Open Access   (Followers: 11)
Algorithms Research     Open Access   (Followers: 1)
American Journal of Biostatistics     Open Access   (Followers: 9)
American Journal of Computational and Applied Mathematics     Open Access   (Followers: 4)
American Journal of Mathematical Analysis     Open Access  
American Journal of Mathematics     Full-text available via subscription   (Followers: 7)
American Journal of Operations Research     Open Access   (Followers: 5)
American Mathematical Monthly     Full-text available via subscription   (Followers: 6)
An International Journal of Optimization and Control: Theories & Applications     Open Access   (Followers: 7)
Analele Universitatii Ovidius Constanta - Seria Matematica     Open Access   (Followers: 1)
Analysis     Hybrid Journal   (Followers: 2)
Analysis and Applications     Hybrid Journal   (Followers: 1)
Analysis and Mathematical Physics     Hybrid Journal   (Followers: 3)
Analysis Mathematica     Full-text available via subscription  
Annales Mathematicae Silesianae     Open Access  
Annales mathématiques du Québec     Hybrid Journal   (Followers: 4)
Annales UMCS, Mathematica     Open Access   (Followers: 1)
Annales Universitatis Paedagogicae Cracoviensis. Studia Mathematica     Open Access  
Annali di Matematica Pura ed Applicata     Hybrid Journal   (Followers: 1)
Annals of Combinatorics     Hybrid Journal   (Followers: 3)
Annals of Data Science     Hybrid Journal   (Followers: 9)
Annals of Discrete Mathematics     Full-text available via subscription   (Followers: 6)
Annals of Mathematics     Full-text available via subscription  
Annals of Mathematics and Artificial Intelligence     Hybrid Journal   (Followers: 6)
Annals of Pure and Applied Logic     Open Access   (Followers: 2)
Annals of the Alexandru Ioan Cuza University - Mathematics     Open Access  
Annals of the Institute of Statistical Mathematics     Hybrid Journal   (Followers: 1)
Annals of West University of Timisoara - Mathematics     Open Access  
Annuaire du Collège de France     Open Access   (Followers: 5)
Applicable Algebra in Engineering, Communication and Computing     Hybrid Journal   (Followers: 2)
Applications of Mathematics     Hybrid Journal   (Followers: 1)
Applied Categorical Structures     Hybrid Journal   (Followers: 2)
Applied Computational Intelligence and Soft Computing     Open Access   (Followers: 12)
Applied Mathematics     Open Access   (Followers: 3)
Applied Mathematics     Open Access   (Followers: 4)
Applied Mathematics & Optimization     Hybrid Journal   (Followers: 4)
Applied Mathematics - A Journal of Chinese Universities     Hybrid Journal  
Applied Mathematics Letters     Full-text available via subscription   (Followers: 1)
Applied Mathematics Research eXpress     Hybrid Journal   (Followers: 1)
Applied Network Science     Open Access   (Followers: 1)
Applied Numerical Mathematics     Hybrid Journal   (Followers: 5)
Applied Spatial Analysis and Policy     Hybrid Journal   (Followers: 4)
Arab Journal of Mathematical Sciences     Open Access   (Followers: 3)
Arabian Journal of Mathematics     Open Access   (Followers: 2)
Archive for Mathematical Logic     Hybrid Journal   (Followers: 1)
Archive of Applied Mechanics     Hybrid Journal   (Followers: 5)
Archive of Numerical Software     Open Access  
Archives of Computational Methods in Engineering     Hybrid Journal   (Followers: 4)
Arkiv för Matematik     Hybrid Journal   (Followers: 1)
Arnold Mathematical Journal     Hybrid Journal   (Followers: 1)
Artificial Satellites : The Journal of Space Research Centre of Polish Academy of Sciences     Open Access   (Followers: 20)
Asia-Pacific Journal of Operational Research     Hybrid Journal   (Followers: 3)
Asian Journal of Algebra     Open Access   (Followers: 1)
Asian Journal of Current Engineering & Maths     Open Access  
Asian-European Journal of Mathematics     Hybrid Journal   (Followers: 2)
Australian Mathematics Teacher, The     Full-text available via subscription   (Followers: 7)
Australian Primary Mathematics Classroom     Full-text available via subscription   (Followers: 2)
Australian Senior Mathematics Journal     Full-text available via subscription   (Followers: 1)
Automatic Documentation and Mathematical Linguistics     Hybrid Journal   (Followers: 5)
Axioms     Open Access  
Baltic International Yearbook of Cognition, Logic and Communication     Open Access  
Basin Research     Hybrid Journal   (Followers: 5)
BIBECHANA     Open Access   (Followers: 1)
BIT Numerical Mathematics     Hybrid Journal  
BoEM - Boletim online de Educação Matemática     Open Access  
Boletim Cearense de Educação e História da Matemática     Open Access  
Boletim de Educação Matemática     Open Access  
Boletín de la Sociedad Matemática Mexicana     Hybrid Journal  
Bollettino dell'Unione Matematica Italiana     Full-text available via subscription   (Followers: 1)
British Journal of Mathematical and Statistical Psychology     Full-text available via subscription   (Followers: 20)
Bruno Pini Mathematical Analysis Seminar     Open Access  
Buletinul Academiei de Stiinte a Republicii Moldova. Matematica     Open Access   (Followers: 8)
Bulletin des Sciences Mathamatiques     Full-text available via subscription   (Followers: 4)
Bulletin of Dnipropetrovsk University. Series : Communications in Mathematical Modeling and Differential Equations Theory     Open Access   (Followers: 1)
Bulletin of Mathematical Sciences     Open Access   (Followers: 1)
Bulletin of the Brazilian Mathematical Society, New Series     Hybrid Journal  
Bulletin of the London Mathematical Society     Hybrid Journal   (Followers: 3)
Bulletin of the Malaysian Mathematical Sciences Society     Hybrid Journal  
Calculus of Variations and Partial Differential Equations     Hybrid Journal  
Canadian Journal of Science, Mathematics and Technology Education     Hybrid Journal   (Followers: 20)
Carpathian Mathematical Publications     Open Access   (Followers: 1)
Catalysis in Industry     Hybrid Journal   (Followers: 1)
CEAS Space Journal     Hybrid Journal  
CHANCE     Hybrid Journal   (Followers: 5)
Chaos, Solitons & Fractals     Hybrid Journal   (Followers: 3)
ChemSusChem     Hybrid Journal   (Followers: 7)
Chinese Annals of Mathematics, Series B     Hybrid Journal  
Chinese Journal of Catalysis     Full-text available via subscription   (Followers: 2)
Chinese Journal of Mathematics     Open Access  
Clean Air Journal     Full-text available via subscription   (Followers: 2)
Cogent Mathematics     Open Access   (Followers: 2)
Cognitive Computation     Hybrid Journal   (Followers: 4)
Collectanea Mathematica     Hybrid Journal  
College Mathematics Journal     Full-text available via subscription   (Followers: 3)
COMBINATORICA     Hybrid Journal  
Combustion Theory and Modelling     Hybrid Journal   (Followers: 13)
Commentarii Mathematici Helvetici     Hybrid Journal   (Followers: 1)
Communications in Contemporary Mathematics     Hybrid Journal  
Communications in Mathematical Physics     Hybrid Journal   (Followers: 1)
Communications On Pure & Applied Mathematics     Hybrid Journal   (Followers: 3)
Complex Analysis and its Synergies     Open Access   (Followers: 2)
Complex Variables and Elliptic Equations: An International Journal     Hybrid Journal  
Complexus     Full-text available via subscription  
Composite Materials Series     Full-text available via subscription   (Followers: 9)
Comptes Rendus Mathematique     Full-text available via subscription   (Followers: 1)
Computational and Applied Mathematics     Hybrid Journal   (Followers: 2)
Computational and Mathematical Methods in Medicine     Open Access   (Followers: 2)
Computational and Mathematical Organization Theory     Hybrid Journal   (Followers: 2)
Computational Complexity     Hybrid Journal   (Followers: 4)
Computational Mathematics and Modeling     Hybrid Journal   (Followers: 8)
Computational Mechanics     Hybrid Journal   (Followers: 4)
Computational Methods and Function Theory     Hybrid Journal  
Computational Optimization and Applications     Hybrid Journal   (Followers: 7)
Computers & Mathematics with Applications     Full-text available via subscription   (Followers: 5)
Concrete Operators     Open Access   (Followers: 4)
Confluentes Mathematici     Hybrid Journal  
COSMOS     Hybrid Journal  
Cryptography and Communications     Hybrid Journal   (Followers: 14)
Cuadernos de Investigación y Formación en Educación Matemática     Open Access  
Cubo. A Mathematical Journal     Open Access  
Czechoslovak Mathematical Journal     Hybrid Journal   (Followers: 1)
Demographic Research     Open Access   (Followers: 11)
Demonstratio Mathematica     Open Access  
Dependence Modeling     Open Access  
Design Journal : An International Journal for All Aspects of Design     Hybrid Journal   (Followers: 28)
Developments in Clay Science     Full-text available via subscription   (Followers: 1)
Developments in Mineral Processing     Full-text available via subscription   (Followers: 3)
Dhaka University Journal of Science     Open Access  
Differential Equations and Dynamical Systems     Hybrid Journal   (Followers: 2)
Discrete Mathematics     Hybrid Journal   (Followers: 8)
Discrete Mathematics & Theoretical Computer Science     Open Access  
Discrete Mathematics, Algorithms and Applications     Hybrid Journal   (Followers: 2)
Discussiones Mathematicae Graph Theory     Open Access   (Followers: 1)
Dnipropetrovsk University Mathematics Bulletin     Open Access  
Doklady Mathematics     Hybrid Journal  
Duke Mathematical Journal     Full-text available via subscription   (Followers: 1)
Edited Series on Advances in Nonlinear Science and Complexity     Full-text available via subscription  
Electronic Journal of Graph Theory and Applications     Open Access   (Followers: 2)
Electronic Notes in Discrete Mathematics     Full-text available via subscription   (Followers: 2)
Elemente der Mathematik     Full-text available via subscription   (Followers: 3)
Energy for Sustainable Development     Hybrid Journal   (Followers: 9)
Enseñanza de las Ciencias : Revista de Investigación y Experiencias Didácticas     Open Access  
Ensino da Matemática em Debate     Open Access  
Entropy     Open Access   (Followers: 5)
ESAIM: Control Optimisation and Calculus of Variations     Full-text available via subscription   (Followers: 1)
European Journal of Combinatorics     Full-text available via subscription   (Followers: 5)
European Journal of Mathematics     Hybrid Journal   (Followers: 1)
European Scientific Journal     Open Access   (Followers: 2)
Experimental Mathematics     Hybrid Journal   (Followers: 4)
Expositiones Mathematicae     Hybrid Journal   (Followers: 2)
Facta Universitatis, Series : Mathematics and Informatics     Open Access  
Fasciculi Mathematici     Open Access  
Finite Fields and Their Applications     Full-text available via subscription   (Followers: 4)
Fixed Point Theory and Applications     Open Access   (Followers: 1)

        1 2 3 4 | Last

Journal Cover Advances in Catalysis
  [SJR: 2.139]   [H-I: 42]   [5 followers]  Follow
   Full-text available via subscription Subscription journal
   ISSN (Print) 0360-0564
   Published by Elsevier Homepage  [3043 journals]
  • Series Page
    • Abstract: Publication date: 2013
      Source:Advances in Catalysis, Volume 56

      PubDate: 2013-12-03T20:19:55Z
  • Paul B. Weisz 1919–2012
    • Abstract: Publication date: 2013
      Source:Advances in Catalysis, Volume 56
      Author(s): Thomas F. Degnan

      PubDate: 2013-12-03T20:19:55Z
  • Haldor Topsøe 1913–2013
    • Abstract: Publication date: 2013
      Source:Advances in Catalysis, Volume 56
      Author(s): Bjerne S. Clausen , James Dumesic

      PubDate: 2013-12-03T20:19:55Z
  • Chapter One Analysis of Catalyst Surface Structure by Physical Sorption
    • Abstract: Publication date: 2013
      Source:Advances in Catalysis, Volume 56
      Author(s): Karl D. Hammond , Wm. Curtis Conner Jr.
      Heterogeneous catalysis usually takes place by sequences of reactions involving fluid-phase reagents and the exposed layer of the solid catalyst surface. Estimation of the total catalyst surface area, its potential accessibility to gas- or liquid-phase reactants, and general catalytic activity are initially based on the morphology of the catalyst. Universally, measurements of adsorption and their interpretation are used to estimate the surface area and porosity relevant to catalytic reactions. We provide here a description of many traditional and recent techniques in adsorption-based catalyst characterization intended for experimental practitioners of adsorption. Our chapter includes descriptions of which regions of the isotherm correspond to micropore filling, mesopore filling, surface coverage, and saturation, supplemented by discussions of model isotherms, from the Langmuir isotherm and the Brunauer–Emmett–Teller theory to the Halsey equation. Pore size distribution methods include the Barrett–Joyner–Halenda and related methods for mesopores, empirical methods developed for micropores, and simulation-based methods that have finally resolved the differences between adsorption (increasing loading) and desorption (decreasing loading). This chapter also includes a discussion of hysteresis and metastability, both of which “trip up” experimentalists from time to time. We finish with a description of data acquisition methods and equipment, which are often obscured behind the facade of automation, and a discussion of what users should be aware of and what can go wrong.

      PubDate: 2013-12-03T20:19:55Z
  • Chapter Two Carbon in Catalysis
    • Abstract: Publication date: 2013
      Source:Advances in Catalysis, Volume 56
      Author(s): Robert Schlögl
      This review is concerned with nanoscale carbon as a catalyst. Elemental carbon has become available in many nanostructured forms representing combinations of the hybridizations found in fundamental carbon allotropes, and the materials can be enriched by a large number of surface functional groups, some generated by nanostructuring. Consequently, many examples of catalytic applications of carbon are documented, but the development of the field has been hampered by the lack of a conceptual approach linking structure and function and by the lack of understanding of synthesis of the materials. This chapter provides a foundation for an advanced comprehension of the catalytic reactivity of carbon and addresses key aspects of characterization and synthesis. The usefulness of X-ray diffraction, Raman spectroscopy, and electron microscopy for the characterization of nanoscale carbons is briefly contrasted with the limitations of these methods. The various structural elements—among them carbon hybridization, local defects, and topology—that contribute to the electronic structure are discussed in detail. The difficulties of analyzing the resulting complex electron spectra are highlighted. In its core part, this chapter uses the derived knowledge of the electronic structure to arrive at concepts illustrating carbon’s potential in catalysis. A general synthesis strategy for the controlled functionalization of carbons is laid out. The ambivalent role of carbon deposits on catalyst surfaces as poisons or an active phase is demonstrated. One-third of the chapter is devoted to two case studies that illustrate the ideas; the catalytic transformations are the oxidative dehydrogenation of ethylbenzene and of alkanes.

      PubDate: 2013-12-03T20:19:55Z
  • Chapter Three Catalytic Deoxygenation Chemistry Upgrading of Liquids
           Derived from Biomass Processing
    • Abstract: Publication date: 2013
      Source:Advances in Catalysis, Volume 56
      Author(s): Tracy J. Benson , Prashant R. Daggolu , Rafael A. Hernandez , Shetian Liu , Mark G. White
      The composition of a typical pyrolysis oil is used to pose the problem of oxygen removal from this oil and to motivate a discussion of the different reactions for oxygen removal that are thermodynamically favored. From a consideration of this thermodynamics analysis of the favored reactions, the surface chemistry literature is surveyed to reveal those materials that allow the adsorption of oxygen-containing species. Included in this survey are experimental and theoretical studies. This consideration of adsorption of oxygen-containing species prompts a further examination of the literature of reaction mechanisms and reaction sequences to reveal the conventional pathways to remove oxygen from the substrates. Moreover, the literature of hydroprocessing is reviewed to show how traditional hydrodesulfurization catalysts have been studied as a hydrodeoxygenation (HDO) catalyst of the reactive species in pyrolysis oils. Furthermore, aqueous-phase reforming is discussed as an alternative to HDO.

      PubDate: 2013-12-03T20:19:55Z
  • Series Page
    • Abstract: 2012
      Publication year: 2012
      Source:Advances in Catalysis, Volume 55

      PubDate: 2012-12-15T09:29:21Z
  • Michel Boudart 1924–2012
    • Abstract: 2012
      Publication year: 2012
      Source:Advances in Catalysis, Volume 55

      PubDate: 2012-12-15T09:29:21Z
  • Chapter One Heterogeneous Catalysis by Gold
    • Abstract: 2012
      Publication year: 2012
      Source:Advances in Catalysis, Volume 55

      Gold can be deposited as nanoparticles (NPs) with diameters of 2–5nm and clusters with diameters less than 2nm on a variety of materials such as oxides, carbides, and sulfides of transition metals, carbons, and organic polymers. Such supported gold NPs and clusters exhibit surprisingly high catalytic activities for many reactions, with both gas- and liquid-phase reactants, in particular, at temperatures below 573K. Until now, more than 10 techniques have been developed for depositing gold as NPs and clusters. The atomic scale structures of supported NPs and clusters have been extensively and intensively investigated with a high-resolution transmission electron microscopy. The mechanisms of catalysis by supported gold NPs have recently been elucidated by using real powder catalysts and model single-crystal catalysts for the low-temperature oxidation of CO. Another simple reaction that has recently been investigated is dihydrogen dissociation, for which gold NP catalysts are still poorly active. Both of these reactions have been demonstrated to take place at perimeter interfaces around the gold NPs. This result means that there is a great chance for gold to exhibit high catalytic activity for hydrogenation reactions by an appropriate choice of metal oxide supports and by minimizing the diameters of gold particles. The catalytic nature of gold clusters has also been investigated theoretically in relation to the effect of cluster size and the influence of organic ligands and polymers. The catalytic performance of gold NPs and clusters has been explored extensively for reactions of both gases and liquids. Supported gold catalysts are useful for air cleaning at room temperature, and they are valuable for green production of bulk and fine chemicals. Supported gold clusters are expected to open new doors for simple chemistry for the selective manufacture of needed products. Size and structure specificity are expected to present opportunities for selective conversions. It is recommended that researchers explore the magic numbers and structures of gold and suitable support materials for selected target reactions.

      PubDate: 2012-12-15T09:29:21Z
  • Chapter Two Ordered Mesoporous Materials as Catalysts
    • Abstract: 2012
      Publication year: 2012
      Source:Advances in Catalysis, Volume 55

      After their discovery in the early 1990s, ordered mesoporous materials have become one of the most widely investigated classes of materials, and applications have been considered in many areas, in particular in catalysis. They have attracted attention because of their unique properties such as high surface areas, controllable compositions, crystallinity, thermal and chemical stability, tailored porosities, narrow pore size distributions, concave surface curvatures, surface functionalities, as well as the opportunities they offer for incorporation of catalytically active and selective species. This chapter is focused on the properties of ordered mesoporous solids that distinguish them from more conventional porous catalytic materials. Emphasis is placed on history, development, and methods of synthesis of ordered mesoporous materials.

      PubDate: 2012-12-15T09:29:21Z
  • Series Page
    • Abstract: 2011
      Publication year: 2011
      Source:Advances in Catalysis, Volume 54

      PubDate: 2012-12-15T09:29:21Z
  • Chapter 1 Designing Molecular Catalysts with Enhanced Lewis Acidity
    • Abstract: 2011
      Publication year: 2011
      Source:Advances in Catalysis, Volume 54

      One of the key challenges in catalysis is the generation of catalytically active metal centers that are highly Lewis acidic so that the metal center can easily bind with a nucleophilic monomer to initiate a catalytic process. With this goal in mind, we pursued the designed synthesis of catalytically active metal centers with enhanced Lewis acidity, adopting two different synthetic strategies. One is the introduction of oxygen between two different metal atoms, and the other is the chemical attachment of highly electronegative fluorine around the catalytically active metal center. The attachment of the oxygen between the two metal centers also brings the metals into close proximity at the molecular level, resulting in a pronounced chemical communication between the metals. The compounds with different metals have often modified the fundamental properties of the individual metal atoms through the well-known “cooperative interaction” that is otherwise difficult to achieve. The synthetic strategy takes advantage of the Brønsted acidic character of the M(OH) moiety in building up a new class of heterometallic complexes. Further, the discovery of Me3SnF as one of the most useful fluorinating reagents for organometallic complexes leads to the successful preparation of organometallic fluorides of Group-4 metals. This synthetic development has resulted in the availability of catalysts of a new class bearing enhanced Lewis acidic metal centers resulting either from oxygen bridging or from the attachment of a highly electronegative fluorine to a catalytically active metal center. In many cases, these complexes have proved to be excellent candidates for olefin polymerization, ring-opening polymerization of caprolactone, olefin epoxidation, and olefin hydroformylation. The improvement in the catalytic properties is a result of the presence of a more electrophilic metal center, which is essential for the catalysis.

      PubDate: 2012-12-15T09:29:21Z
  • Chapter 2 Modern Strategies in Supramolecular Catalysis
    • Abstract: 2011
      Publication year: 2011
      Source:Advances in Catalysis, Volume 54

      This chapter summarizes the main achievements in the area of supramolecular catalysis in the past decade. Supramolecular chemistry emerged 40 years ago. The initial focus was host–guest chemistry, and one target application was the use of such interactions to bring catalyst and substrate together. Examples in the first part of this chapter illustrate how rates of reactions, selectivities, regioselectivities, and enantioselectivities may change through assemblies designed as models for enzymes. In the beginning, natural host molecules such as cyclodextrins and modified cyclodextrins received most attention, but later a plethora of synthetic hosts were developed. More recently, the construction of host molecules was facilitated enormously by the introduction of supramolecular “tools”; according to this principle, large entities are constructed by bringing together smaller building blocks via noncovalent forces, such as hydrogen bonding, ionic bonding, metal–ligand coordination bonding, fluorophilic interactions, etc. A large number of host molecules were reported in the past decade, and most of them do not function merely as hosts but instead are containers that can host more than one molecule and have catalytic functions incorporated. A variety of names are used for these entities, such as capsule, cavitand, nanoreactor, nanocontainer, cage molecule, and receptor molecule. Large changes in selectivities and rates of catalytic reactions relative to those of bare catalytic sites have been reported. The second part of this chapter deals with the supramolecular construction of ligands or entire catalyst assemblies. This modular construction has enabled the synthesis of large catalyst libraries, which are useful for catalyst optimization and catalyst screening. In this way, new catalysts were developed, and new ways to control rates and selectivities of catalytic reactions were recognized. Biomacromolecules (and modified variants) have been used, particularly as sources of chirality in catalytic transformations, via supramolecular interactions with homogeneous catalysts. The last part of the chapter shows that supramolecular interactions can be used successfully for the immobilization of homogeneous catalysts. By its nature, the bonding is reversible, and the developments have led to a new reactor configuration for use of homogeneous catalysts, termed reverse-flow adsorption.

      PubDate: 2012-12-15T09:29:21Z
  • Chapter 3 Mechanistic Issues in Fischer–Tropsch Catalysis
    • Abstract: 2011
      Publication year: 2011
      Source:Advances in Catalysis, Volume 54

      Computational studies have recently generated important information regarding reaction intermediates and activation barriers of elementary reaction steps that are part of the Fischer–Tropsch synthesis. We use these results to analyze various mechanistic options that have been proposed for the Fischer–Tropsch synthesis. The computational results do not support the Pichler–Schulz chain-growth mechanism, which postulates chain growth by CO insertion. Rather, the results are in agreement with the Sachtler–Biloen mechanism, which postulates chain growth via adsorbed “C1” species; furthermore, the Gaube chain-growth mechanism, which closely resembles that proposed by Maitlis, is found to be preferred over the initially assumed Brady–Pettit mechanism. The various elementary steps are discussed, and the values that their relative rates must assume for successful Fischer–Tropsch chain growth are outlined. Within the Sachtler–Biloen kinetics scheme, a high chain-growth probability is obtained when chain termination is rate limiting. Consequently, CO dissociation has to be facile. The “C1” species that is incorporated into the growing chain appears to be “CH” or “CH2”; thus, these species must be present in high surface concentrations. Brønsted–Evans–Polanyi relationships are used to link activation energies to surface reactivity. The structure sensitivity of the elementary reaction steps, specifically, initiation, chain growth, and termination, is analyzed. On the basis of these considerations, one can understand why particular metals are suitable Fischer–Tropsch catalysts.

      PubDate: 2012-12-15T09:29:21Z
  • Chapter 4 Vanadium Phosphate Materials as Selective Oxidation Catalysts
    • Abstract: 2011
      Publication year: 2011
      Source:Advances in Catalysis, Volume 54

      Vanadium phosphates have been established as selective hydrocarbon oxidation catalysts for more than 40 years. Their primary use commercially has been in the production of maleic anhydride (MA) from n-butane. During this period, improvements in the yield of MA have been sought. Strategies to achieve these improvements have included the addition of secondary metal ions to the catalyst, optimization of the catalyst precursor formation, and intensification of the selective oxidation process through improved reactor technology. The mechanism of the reaction continues to be an active subject of research, and the role of the bulk catalyst structure and an amorphous surface layer are considered here with respect to the various V–P–O phases present. The active site of the catalyst is considered to consist of V4+ and V5+ couples, and their respective incidence and roles are examined in detail here. The complex and extensive nature of the oxidation, which for butane oxidation to MA is a 14-electron transfer process, is of broad importance, particularly in view of the applications of vanadium phosphate catalysts to other processes. A perspective on the future use of vanadium phosphate catalysts is included in this review.

      PubDate: 2012-12-15T09:29:21Z
  • Chapter 5 Monolithic Catalysts and Reactors High Precision with Low Energy
    • Abstract: 2011
      Publication year: 2011
      Source:Advances in Catalysis, Volume 54

      Structured catalysts and reactors offer high precision in catalysis at all relevant scales of the catalytic process, from that of the catalytic species up to that of the reactor. Monoliths are the prime example of such catalysts because of their wide practical applications. Thus, monoliths are emphasized in this review, but most of the text is also relevant to all structured reactors, including microreactors. Conceptually, monoliths exhibit more degrees of freedom in design than conventional reactors, such as fixed-bed and slurry reactors. The flow in monoliths is laminar, and as a consequence, they are associated with high efficiency and minimum chaotic characteristics. The hydrodynamics of single-phase and multiphase flow reactors are remarkably simple. Under most conditions in multiphase systems, Taylor flow (segmented flow) prevails, associated with high rates of mass transfer notwithstanding low energy consumption, but under other conditions, the film flow regime can be realized either in cocurrent or in countercurrent flow of gas and liquid streams, making the monolith a good structure for novel technologies such as catalytic distillation. Monoliths offer freedom in the design of reactor configuration. Examples are loop reactors for strong exo- and endothermic reactions, which allow a combination with separate heat exchange without the penalty of a large energy consumption, which otherwise is usually unavoidable for the large recycle ratios needed. For applications in fine chemistry and in the laboratory, a convenient monolithic stirred reactor is presented. The principal bottleneck for practical application of monolith reactors is the synthesis rather than the design of the catalytic monolith. When a monolith reactor is considered as an alternative to a fixed-bed reactor packed with commercially available catalyst particles, the grim reality is that a development program is needed to producing the catalytic monolith. Therefore, preparation methods including synthesis of various coating layers and the deposition of active catalytic species are described in detail here. This chapter also includes an exhaustive review of practical applications of monolith reactors. In applications in which high gas flow rates have to be accommodated, monoliths monoliths are the state of the art in many cases, exemplified by automobile exhaust abatement reactors—because of the popularity of automobiles, more monolithic reactors are being used than fixed-bed reactors. Applications in processes with liquid-phase and gas–liquid-phase reactants are scarce, but one well-known commercial process (the reduction step in the production of hydrogen peroxide) shows the feasibility of monoliths. Several processes are in the development stage. Included in the review are an assessment of the impact of these reactors on process intensification and applications in biotechnology and photocatalysis.

      PubDate: 2012-12-15T09:29:21Z
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