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  Subjects -> COMPUTER SCIENCE (Total: 1988 journals)
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COMPUTER SCIENCE (1153 journals)                  1 2 3 4 5 6 | Last

Showing 1 - 200 of 872 Journals sorted alphabetically
3D Printing and Additive Manufacturing     Full-text available via subscription   (Followers: 14)
Abakós     Open Access   (Followers: 3)
Academy of Information and Management Sciences Journal     Full-text available via subscription   (Followers: 68)
ACM Computing Surveys     Hybrid Journal   (Followers: 22)
ACM Journal on Computing and Cultural Heritage     Hybrid Journal   (Followers: 9)
ACM Journal on Emerging Technologies in Computing Systems     Hybrid Journal   (Followers: 13)
ACM Transactions on Accessible Computing (TACCESS)     Hybrid Journal   (Followers: 3)
ACM Transactions on Algorithms (TALG)     Hybrid Journal   (Followers: 16)
ACM Transactions on Applied Perception (TAP)     Hybrid Journal   (Followers: 6)
ACM Transactions on Architecture and Code Optimization (TACO)     Hybrid Journal   (Followers: 9)
ACM Transactions on Autonomous and Adaptive Systems (TAAS)     Hybrid Journal   (Followers: 7)
ACM Transactions on Computation Theory (TOCT)     Hybrid Journal   (Followers: 11)
ACM Transactions on Computational Logic (TOCL)     Hybrid Journal   (Followers: 4)
ACM Transactions on Computer Systems (TOCS)     Hybrid Journal   (Followers: 18)
ACM Transactions on Computer-Human Interaction     Hybrid Journal   (Followers: 12)
ACM Transactions on Computing Education (TOCE)     Hybrid Journal   (Followers: 3)
ACM Transactions on Design Automation of Electronic Systems (TODAES)     Hybrid Journal   (Followers: 1)
ACM Transactions on Economics and Computation     Hybrid Journal  
ACM Transactions on Embedded Computing Systems (TECS)     Hybrid Journal   (Followers: 4)
ACM Transactions on Information Systems (TOIS)     Hybrid Journal   (Followers: 20)
ACM Transactions on Intelligent Systems and Technology (TIST)     Hybrid Journal   (Followers: 9)
ACM Transactions on Interactive Intelligent Systems (TiiS)     Hybrid Journal   (Followers: 4)
ACM Transactions on Multimedia Computing, Communications, and Applications (TOMCCAP)     Hybrid Journal   (Followers: 10)
ACM Transactions on Reconfigurable Technology and Systems (TRETS)     Hybrid Journal   (Followers: 7)
ACM Transactions on Sensor Networks (TOSN)     Hybrid Journal   (Followers: 8)
ACM Transactions on Speech and Language Processing (TSLP)     Hybrid Journal   (Followers: 11)
ACM Transactions on Storage     Hybrid Journal  
ACS Applied Materials & Interfaces     Full-text available via subscription   (Followers: 21)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 3)
Acta Universitatis Cibiniensis. Technical Series     Open Access  
Ad Hoc Networks     Hybrid Journal   (Followers: 11)
Adaptive Behavior     Hybrid Journal   (Followers: 11)
Advanced Engineering Materials     Hybrid Journal   (Followers: 26)
Advanced Science Letters     Full-text available via subscription   (Followers: 7)
Advances in Adaptive Data Analysis     Hybrid Journal   (Followers: 8)
Advances in Artificial Intelligence     Open Access   (Followers: 16)
Advances in Calculus of Variations     Hybrid Journal   (Followers: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5)
Advances in Computational Mathematics     Hybrid Journal   (Followers: 15)
Advances in Computer Science : an International Journal     Open Access   (Followers: 13)
Advances in Computing     Open Access   (Followers: 2)
Advances in Data Analysis and Classification     Hybrid Journal   (Followers: 54)
Advances in Engineering Software     Hybrid Journal   (Followers: 25)
Advances in Geosciences (ADGEO)     Open Access   (Followers: 10)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 25)
Advances in Human-Computer Interaction     Open Access   (Followers: 20)
Advances in Materials Sciences     Open Access   (Followers: 16)
Advances in Operations Research     Open Access   (Followers: 11)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7)
Advances in Porous Media     Full-text available via subscription   (Followers: 4)
Advances in Remote Sensing     Open Access   (Followers: 37)
Advances in Science and Research (ASR)     Open Access   (Followers: 6)
Advances in Technology Innovation     Open Access   (Followers: 1)
AEU - International Journal of Electronics and Communications     Hybrid Journal   (Followers: 8)
African Journal of Information and Communication     Open Access   (Followers: 6)
African Journal of Mathematics and Computer Science Research     Open Access   (Followers: 4)
Air, Soil & Water Research     Open Access   (Followers: 7)
AIS Transactions on Human-Computer Interaction     Open Access   (Followers: 6)
Algebras and Representation Theory     Hybrid Journal   (Followers: 1)
Algorithms     Open Access   (Followers: 11)
American Journal of Computational and Applied Mathematics     Open Access   (Followers: 4)
American Journal of Computational Mathematics     Open Access   (Followers: 4)
American Journal of Information Systems     Open Access   (Followers: 7)
American Journal of Sensor Technology     Open Access   (Followers: 2)
Anais da Academia Brasileira de Ciências     Open Access   (Followers: 2)
Analog Integrated Circuits and Signal Processing     Hybrid Journal   (Followers: 5)
Analysis in Theory and Applications     Hybrid Journal   (Followers: 1)
Animation Practice, Process & Production     Hybrid Journal   (Followers: 5)
Annals of Combinatorics     Hybrid Journal   (Followers: 3)
Annals of Data Science     Hybrid Journal   (Followers: 9)
Annals of Mathematics and Artificial Intelligence     Hybrid Journal   (Followers: 6)
Annals of Pure and Applied Logic     Open Access   (Followers: 2)
Annals of Software Engineering     Hybrid Journal   (Followers: 12)
Annual Reviews in Control     Hybrid Journal   (Followers: 6)
Anuario Americanista Europeo     Open Access  
Applicable Algebra in Engineering, Communication and Computing     Hybrid Journal   (Followers: 2)
Applied and Computational Harmonic Analysis     Full-text available via subscription   (Followers: 2)
Applied Artificial Intelligence: An International Journal     Hybrid Journal   (Followers: 14)
Applied Categorical Structures     Hybrid Journal   (Followers: 2)
Applied Clinical Informatics     Hybrid Journal   (Followers: 2)
Applied Computational Intelligence and Soft Computing     Open Access   (Followers: 12)
Applied Computer Systems     Open Access   (Followers: 1)
Applied Informatics     Open Access  
Applied Mathematics and Computation     Hybrid Journal   (Followers: 32)
Applied Medical Informatics     Open Access   (Followers: 10)
Applied Numerical Mathematics     Hybrid Journal   (Followers: 5)
Applied Soft Computing     Hybrid Journal   (Followers: 16)
Applied Spatial Analysis and Policy     Hybrid Journal   (Followers: 4)
Architectural Theory Review     Hybrid Journal   (Followers: 3)
Archive of Applied Mechanics     Hybrid Journal   (Followers: 4)
Archive of Numerical Software     Open Access  
Archives and Museum Informatics     Hybrid Journal   (Followers: 120)
Archives of Computational Methods in Engineering     Hybrid Journal   (Followers: 4)
Artifact     Hybrid Journal   (Followers: 2)
Artificial Life     Hybrid Journal   (Followers: 6)
Asia Pacific Journal on Computational Engineering     Open Access  
Asia-Pacific Journal of Information Technology and Multimedia     Open Access   (Followers: 1)
Asian Journal of Computer Science and Information Technology     Open Access  
Asian Journal of Control     Hybrid Journal  
Assembly Automation     Hybrid Journal   (Followers: 2)
at - Automatisierungstechnik     Hybrid Journal   (Followers: 1)
Australian Educational Computing     Open Access  
Automatic Control and Computer Sciences     Hybrid Journal   (Followers: 3)
Automatic Documentation and Mathematical Linguistics     Hybrid Journal   (Followers: 5)
Automatica     Hybrid Journal   (Followers: 9)
Automation in Construction     Hybrid Journal   (Followers: 6)
Autonomous Mental Development, IEEE Transactions on     Hybrid Journal   (Followers: 8)
Basin Research     Hybrid Journal   (Followers: 5)
Behaviour & Information Technology     Hybrid Journal   (Followers: 52)
Bioinformatics     Hybrid Journal   (Followers: 246)
Biomedical Engineering     Hybrid Journal   (Followers: 16)
Biomedical Engineering and Computational Biology     Open Access   (Followers: 13)
Biomedical Engineering, IEEE Reviews in     Full-text available via subscription   (Followers: 17)
Biomedical Engineering, IEEE Transactions on     Hybrid Journal   (Followers: 32)
Briefings in Bioinformatics     Hybrid Journal   (Followers: 45)
British Journal of Educational Technology     Hybrid Journal   (Followers: 124)
Broadcasting, IEEE Transactions on     Hybrid Journal   (Followers: 10)
c't Magazin fuer Computertechnik     Full-text available via subscription   (Followers: 2)
CALCOLO     Hybrid Journal  
Calphad     Hybrid Journal  
Canadian Journal of Electrical and Computer Engineering     Full-text available via subscription   (Followers: 14)
Catalysis in Industry     Hybrid Journal   (Followers: 1)
CEAS Space Journal     Hybrid Journal  
Cell Communication and Signaling     Open Access   (Followers: 1)
Central European Journal of Computer Science     Hybrid Journal   (Followers: 5)
CERN IdeaSquare Journal of Experimental Innovation     Open Access  
Chaos, Solitons & Fractals     Hybrid Journal   (Followers: 3)
Chemometrics and Intelligent Laboratory Systems     Hybrid Journal   (Followers: 15)
ChemSusChem     Hybrid Journal   (Followers: 7)
China Communications     Full-text available via subscription   (Followers: 7)
Chinese Journal of Catalysis     Full-text available via subscription   (Followers: 2)
CIN Computers Informatics Nursing     Full-text available via subscription   (Followers: 12)
Circuits and Systems     Open Access   (Followers: 16)
Clean Air Journal     Full-text available via subscription   (Followers: 2)
CLEI Electronic Journal     Open Access  
Clin-Alert     Hybrid Journal   (Followers: 1)
Cluster Computing     Hybrid Journal   (Followers: 1)
Cognitive Computation     Hybrid Journal   (Followers: 4)
COMBINATORICA     Hybrid Journal  
Combustion Theory and Modelling     Hybrid Journal   (Followers: 13)
Communication Methods and Measures     Hybrid Journal   (Followers: 11)
Communication Theory     Hybrid Journal   (Followers: 19)
Communications Engineer     Hybrid Journal   (Followers: 1)
Communications in Algebra     Hybrid Journal   (Followers: 3)
Communications in Partial Differential Equations     Hybrid Journal   (Followers: 3)
Communications of the ACM     Full-text available via subscription   (Followers: 53)
Communications of the Association for Information Systems     Open Access   (Followers: 18)
COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering     Hybrid Journal   (Followers: 3)
Complex & Intelligent Systems     Open Access  
Complex Adaptive Systems Modeling     Open Access  
Complex Analysis and Operator Theory     Hybrid Journal   (Followers: 2)
Complexity     Hybrid Journal   (Followers: 6)
Complexus     Full-text available via subscription  
Composite Materials Series     Full-text available via subscription   (Followers: 9)
Computación y Sistemas     Open Access  
Computation     Open Access  
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 and Structural Biotechnology Journal     Open Access   (Followers: 2)
Computational and Theoretical Chemistry     Hybrid Journal   (Followers: 9)
Computational Astrophysics and Cosmology     Open Access   (Followers: 1)
Computational Biology and Chemistry     Hybrid Journal   (Followers: 12)
Computational Chemistry     Open Access   (Followers: 2)
Computational Cognitive Science     Open Access   (Followers: 2)
Computational Complexity     Hybrid Journal   (Followers: 4)
Computational Condensed Matter     Open Access  
Computational Ecology and Software     Open Access   (Followers: 8)
Computational Economics     Hybrid Journal   (Followers: 9)
Computational Geosciences     Hybrid Journal   (Followers: 14)
Computational Linguistics     Open Access   (Followers: 23)
Computational Management Science     Hybrid Journal  
Computational Mathematics and Modeling     Hybrid Journal   (Followers: 8)
Computational Mechanics     Hybrid Journal   (Followers: 4)
Computational Methods and Function Theory     Hybrid Journal  
Computational Molecular Bioscience     Open Access   (Followers: 2)
Computational Optimization and Applications     Hybrid Journal   (Followers: 7)
Computational Particle Mechanics     Hybrid Journal   (Followers: 1)
Computational Research     Open Access   (Followers: 1)
Computational Science and Discovery     Full-text available via subscription   (Followers: 2)
Computational Science and Techniques     Open Access  
Computational Statistics     Hybrid Journal   (Followers: 13)
Computational Statistics & Data Analysis     Hybrid Journal   (Followers: 29)
Computer     Full-text available via subscription   (Followers: 84)
Computer Aided Surgery     Hybrid Journal   (Followers: 3)
Computer Applications in Engineering Education     Hybrid Journal   (Followers: 6)
Computer Communications     Hybrid Journal   (Followers: 10)
Computer Engineering and Applications Journal     Open Access   (Followers: 5)
Computer Journal     Hybrid Journal   (Followers: 7)
Computer Methods in Applied Mechanics and Engineering     Hybrid Journal   (Followers: 22)
Computer Methods in Biomechanics and Biomedical Engineering     Hybrid Journal   (Followers: 10)
Computer Methods in the Geosciences     Full-text available via subscription   (Followers: 1)
Computer Music Journal     Hybrid Journal   (Followers: 14)
Computer Physics Communications     Hybrid Journal   (Followers: 6)
Computer Science - Research and Development     Hybrid Journal   (Followers: 7)
Computer Science and Engineering     Open Access   (Followers: 17)
Computer Science and Information Technology     Open Access   (Followers: 11)
Computer Science Education     Hybrid Journal   (Followers: 12)
Computer Science Journal     Open Access   (Followers: 20)
Computer Science Master Research     Open Access   (Followers: 10)

        1 2 3 4 5 6 | 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
           Consumption
    • 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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