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Showing papers in "Studies in Surface Science and Catalysis in 2001"


Journal ArticleDOI
TL;DR: In this paper, the methods of obtaining various mesostructures made of nanocrystals are described, and collective optical, magnetic, and transport properties are demonstrated by applying a magnetic field during the deposition process.
Abstract: In this feature article, the methods of obtaining various mesostructures made of nanocrystals are described. With silver and silver sulfide, the nanocrystals are able to self organize in 2D and 3D super lattices to form “supra” crystals. With cobalt and ferrites nanocrystals, it has been possible to make ribbons, dots, or labyrinths. These mesostructures present new physical properties differing from those of the isolated nanocrystal and from those of the bulk phase. Collective optical, magnetic, and transport properties are demonstrated. By applying a magnetic field during the deposition process of nanocrystals, the easy axes of the particles are oriented along the direction of the applied field, inducing again the collective magnetic properties.

489 citations


Book ChapterDOI
TL;DR: The history of zeolites and molecular sieves is reviewed from the discovery of the first zeolite mineral in 1756 through the explosion in new molecular sieve structures and compositions in the 1980's as mentioned in this paper.
Abstract: The history of zeolites and molecular sieves is reviewed from the discovery of the first zeolite mineral in 1756 through the explosion in new molecular sieve structures and compositions in the 1980's. R. M. Barrer's early pioneering work in adsorption and synthesis began the era of synthetic zeolites. The discovery of the commercially significant synthetic zeolites A, X and Y by R. M. Milton and D. W. Breck in the late 1940's to early 1950's led to their introduction by Union Carbide Corporation as a new class of industrial adsorbents in 1954, and in 1959 as hydrocarbon conversion catalysts. Today they are used widely throughout the petroleum refining and chemical process industries as selective adsorbents, catalysts and ion exchangers, and represent an estimated quarter of a billion dollar industry. The last four decades have seen a chronological progression in molecular sieve materials from the aluminosilicate zeolites to the microporous silica polymorphs to the microporous aluminophosphate-based polymorphs and metallosilicate compositions.

126 citations


Book ChapterDOI
TL;DR: In this paper, the Si, Al ordering pattern depends on the size, charge, and placing of the original extra-framework cations, and it is shown that the Si-Al ordering pattern exhibits different properties depending on the degree and type of Si-al ordering.
Abstract: Structural peculiarities of clinoptilolite and heulandite are reviewed. Special attention is given to partial Si, Al ordering within the tetrahedral framework structure. There is strong evidence that the Si, Al ordering pattern depends on the size, charge, and placing of the original extraframework cations. Even if exchanged to homoionic forms clinoptilolite and heulandite may display different properties depending on the degree and type of Si, Al ordering. In some cation-exchanged heulandites symmetry lowering from the topological symmetry C2/m to Cm or C1 has been observed due to partial Si, Al ordering and low symmetry site preference of extraframework cations. Major applications of clinoptilolite are reviewed. In the field of pollution abatement not only the natural product but also surface modified clinoptilolites gain importance.

122 citations


Book ChapterDOI
TL;DR: In this article, the interaction of transport and kinetics in catalytic monoliths used for natural gas conversion is studied experimentally and numerically, focusing on precise flow field agreement between experiment and model.
Abstract: The interaction of transport and kinetics in catalytic monoliths used for natural gas conversion is studied experimentally and numerically. The paper focuses on a precise flow field agreement between experiment and model. Therefore, we use extruded monoliths with rectangular channel cross-section and a three-dimensional Navier-Stokes simulation including detailed reaction mechanisms and a heat balance. Latter also accounts for heat conducting channel walls and external heat loss. If a washcoat is used, a set of one-dimensional reaction-diffusion equations is additionally applied for modeling the transport and heterogeneous reactions in the washcoat. Partial oxidation of methane to synthesis gas on rhodium coated monoliths has been studied as example.

114 citations


Book ChapterDOI
TL;DR: In this paper, the main theme of this chapter is a discussion of selective oxidation catalysis by framework species in molecular sieves, and the so-called "ship-in-a-bottle" catalysts are described.
Abstract: Publisher Summary Selective oxidation reactions are applied throughout the chemical industry to produce chemicals ranging from bulk scale oxygenates to pharmaceuticals. For obvious economical and environmental reasons, most bulk scale oxidation processes are catalytic and most employ air or oxygen as the oxidant. Catalytic methods are for the last two decades also gaining ground in fine chemicals production, albeit at a fairly slow pace, because it is often more difficult to justify the significant research efforts needed to find and develop them. This chapter discusses some interesting examples of selective oxidation catalysis with ion-exchanged systems, before going to what is the main theme of this chapter: oxidation catalysis by framework species in molecular sieves. Zeolite entrapped metal complexes with organic ligands, the so-called “ship-in-a-bottle” catalysts, are also described.

73 citations


Book ChapterDOI
TL;DR: The Oslo SantaBarbara (OSB)-1 and OSB-2 topologies as mentioned in this paper are based on three-ring architectures and are chiral and formed by a double helix chain out of three-rings.
Abstract: Publisher Summary This chapter discusses very open microporous materials. Two new zeolite topologies—namely, OsloSantaBarbara (OSB)-1 and -2––are presented. These structures are based on three-ring architectures. OSB-1 is the first example of a zeolite topology constructed from three-rings only. The 14-ring channels are chiral and formed by a double helix chain out of three-rings. The OSB-2 structure possesses the most open, noninterrupted framework ever.

72 citations


Book ChapterDOI
TL;DR: In this article, a review of aspects of ion exchange in zeolites is presented, with special reference to those properties of zeolite which give rise to characteristic, and sometimes unique, ion exchange behaviour.
Abstract: Summary Aspects of ion exchange in zeolites are reviewed, with special reference to those properties of zeolites which give rise to characteristic, and sometimes unique, ion exchange behaviour. As well as discussing basic principles, some thermodynamic and kinetic aspects of the theory of ion exchange are covered with particular reference to their utility for predicting exchange behaviour in zeolites and for the use of ion exchange technqiues in detergency building, radionuclide separation, waste water treatment and the preparation of zeolitic catalysts and sorbents. Recent developments on the use of zeolites in detergency are next reviewed, in more detail, together with progress in the field of ion exchange using high silica zeolites or solid state techniques.

69 citations


Book ChapterDOI
TL;DR: The template synthesis of ordered mesoporous carbon (OMC) molecular sieves is discussed in this paper, where the template is removed after template removal to obtain transmission electron microscopy images and X-ray diffraction (XRD) patterns characteristic of the ordered arrangement of uniform mesopores.
Abstract: Publisher Summary This chapter discusses the template synthesis of ordered mesoporous carbon (OMC) molecular sieves. OMC of various structures, designated as CMK-1∼5, have been synthesized by the carbonization of sucrose, furfuryl alcohol, or other carbon sources inside silica or aluminosilicate mesopores that are interconnected into three-dimensional networks, such as in MCM-48, SBA-1, and SBA-15. The mesoporous carbon molecular sieves, obtained after template removal, show transmission electron microscopy (TEM) images and X-ray diffraction (XRD) patterns characteristic of the ordered arrangement of uniform mesopores. The OMC, which are opening up a new area of the nanoporous materials, exhibit high Brunauer–Emmett–Telle (BET) specific surface areas, excellent thermal stability in inert atmospheres, and strong resistance to attack by acids and bases.

64 citations


Book ChapterDOI
Abstract: Publisher Summary Information on the structural, chemical, and catalytic characteristics of zeolites is essential for deriving relations between their chemical and physicochemical properties on the one side and the sorptive and catalytic properties on the other. Such relations are of high importance, as they allow the rational development of sorbents, catalysts, and advanced structural materials. Individual analysis techniques typically probe only a particular aspect of the material and, consequently, a combination of methods is necessary to give a balanced description of the frequently complex zeolite. This places a high experimental demand upon a chemist or physicist who seeks to use and improve a microporous material for a dedicated purpose. Of the three main uses of zeolites, as cation-exchangers, sorbents/hosts and catalysts, only characterization with respect to the latter two applications are being dealt with in depth in this chapter.

60 citations


Book ChapterDOI
TL;DR: In this paper, an overview of existing and new catalytic applications of zeolites in oil refining and gas conversion is presented. And the unique opportunities and limitations of the zeolite catalysts are discussed in order to put the applications in hydrocarbon processing into perspective.
Abstract: This chapter on hydrocarbon processing with zeolites covers both existing and new catalytic applications of zeolites in oil refining and gas conversion. By way of introduction some structural aspects related to these industries are discussed to provide some background in which to relate the current and future developments. Further, the unique opportunities and limitations of zeolites are discussed in order to put the applications in hydrocarbon processing into perspective. Some more evolutionary type developments are covered where the introduction and continued improvement of zeolite catalysts have had a significant impact on existing process technologies. Examples of such technologies in this category include catalytic cracking, hydrocracking, paraffin isomerization and olefin oligomerization. Newer process technologies in which the application of zeolitic catalysts has led to new process concepts are also included. The unique shape selective properties of zeolites are shown to play a dominant role in this developing field of applications. Examples include catalytic iso-dewaxing, LPG to aromatics (CYCLAR), selective oxidation, methanol-toolefins (MTO), deep catalytic cracking (DCC) and selective catalytic NOx removal (SCR). Finally, some general trends are discussed in terms of zeolite catalysis and how these might be expected to have a further impact on hydrocarbon process technology in the future. Significant opportunities are believed to exist for further developments related to both existing and emerging processes. The discovery and application of new synthetic molecular sieves, leading to new or rejuvenated processes, also holds promise for the future. In addition, advances in understanding are being achieved by the recent emphasis on theoretical studies, while the emerging combinatorial synthesis and high-speed screening technologies represent a great increase in experimental power over the time-consuming and empirical approaches employed hitherto.

58 citations



Book ChapterDOI
TL;DR: In this paper, secondary or post-synthesis treatments have been utilized to produce many of the desired catalytic properties that could not be achieved by direct synthesis, such as increased catalytic acid activity, improved thermal and hydrothermal stability, and extra porosity.
Abstract: Summary Secondary or post-synthesis treatments have been utilized to produce many of the desired catalytic properties that could not be achieved by direct synthesis. These include increased catalytic acid activity, improved thermal and hydrothermal stability, and extra porosity. Historically, research in this area has been driven by the demand for improved petroleum cracking catalysts. Treatments used include: acid leaching, high temperature steam, and chemical treatments with chelates or fluoride compounds as well as combinations of these treatments. These processes are described along with the effects these methods have on the structural, physical and catalytic properties of the material.

Book ChapterDOI
TL;DR: In this paper, a conceptual basis for rationalizing acid zeolite based catalytic hydrocarbon conversion processes is provided with a conceptual framework to explain the reactivity and selectivity of the catalytic catalyst without considering the chemical and physical interactions of the hydrocarbon molecules with the Zeolite framework.
Abstract: Publisher Summary Catalytic conversion of hydrocarbons over crystalline microporous acidic aluminosilicate catalysts is applied in large petroleum refining processes including catalytic cracking, hydro cracking, isomerization, alkylation, and oligomerization. This chapter provides with a conceptual basis for rationalizing this acid zeolite based catalytic hydrocarbon conversion processes. It is recognized that the zeolite acid strength is more in line with conventional strong acids rather than with superacid. In order to explain the reactivity and the selectivity of the zeolite catalyst, it is insufficient to represent the zeolite catalyst by a proton, by analogy to homogeneous strong BrOnsted acids, without considering the chemical and physical interactions of the hydrocarbon molecules with the zeolite framework. The kinetics of the catalytic conversions are dominated by the strong physical adsorption of the molecules on the catalyst being unique to zeolites.


Book ChapterDOI
Stephen T. Wilson1
TL;DR: The first aluminophosphate molecular sieve, A1PO4-5, was synthesized in 1978 using Pr4NOH as template and synthesis conditions significantly different from those of zeolites.
Abstract: The first aluminophosphate molecular sieve, A1PO4-5, was synthesized in 1978 using Pr4NOH as template and synthesis conditions significantly different from those of zeolites. Using readily accessible organic amines and quaternary ammonium hydroxides as structure directing agents, over 20 structures, large, medium and small pore, were discovered within a few years, many of them unobtainable in zeolites. Framework elements such as Si, Mg, Co, Mn, and Ti were incorporated into the A1PO4 lattice, producing Bronsted acidity or redox activity. By 2000 the number of structures rose to over 50 as new phosphate-based compositions and novel synthesis media were explored. Remarkable structures with very large pore sizes, such as VPI-5 and cloverite, received a lot of attention and aroused some controversies. The number of elements that can be incorporated into phosphate-based molecular sieves is currently greater than 15. Although novel templates were initially the primary source of this structural diversity, other synthesis modifications quickly led to new families of materials. The recent preparation and structural analysis of chain and sheet-like aluminophosphate structures has led to speculation that these may be similar to intermediates in the formation of A1PO4-based molecular sieves and thus may provide mechanistic clues. Most of the catalytic interest has centered on SAPO' s which have weak to moderate Bronsted acidity and two of these have been commercialized, SAPO-11 in lube oil dewaxing by Chevron and SAPO-34 in methanol-to-olefins conversion by UOP/Norsk Hydro. Spurred by the success of TS-1 in oxidation catalysis, there is renewed interest in Ti, Co, V, Mn and Cr substituted A1PO4-based molecular sieves for selective partial oxidation.

Book ChapterDOI
TL;DR: The main feature of a zeolite structure is its framework type, which describes the arrangement of the cages, the dimensionality of the channel system and the approximate size of the pore openings.
Abstract: Publisher Summary This chapter presents the beauty and diversity of zeolite framework structures, to introduce some of the jargon used to describe them, and to outline some of the techniques used to characterize them. The main feature of a zeolite structure is its framework type, which describes the arrangement of the cages, the dimensionality of the channel system and the approximate size of the pore openings. A few framework types, selected for their industrial relevance and/or to illustrate some of the more common structural nomenclature, have been presented. However, there are many more, and for more information about a specific framework type. To fully understand the properties of a real zeolitic material though, not only the framework type, but also the composition and true geometry of the framework, the location and nature of the extra-framework species, and the number and type of defects must be investigated.

Book ChapterDOI
TL;DR: The main focus of as mentioned in this paper is on the experimental techniques and their advantages and limitations, highlighting the agreement and discrepancies between different measurement techniques and the observed trends of diffusivity and activation energy with molecular size/shape, zeolite composition and channel geometry.
Abstract: Intracrystalline diffusion of adsorbed molecules in zeolite crystals is critically important in relation to the application of zeolites as adsorbents and shape selective catalysts. Over the past fifty years this subject has attracted considerable research, aimed both at developing improved experimental methods for measurement of intracrystalline diffusion and at increasing our basic understanding of the transport mechanism. The main focus of this chapter is on the experimental techniques and their advantages and limitations. This is followed by a review of some of the reported diffusivity values, highlighting the agreement and discrepancies between different measurement techniques and the observed trends of diffusivity and activation energy with molecular size/shape, zeolite composition and channel geometry. The final section focuses on the quantitative relationship between zeolite diffusion and catalyst activity.

Book ChapterDOI
TL;DR: The mechanism of formation of whisker carbon has been studied over the last 30 years as discussed by the authors, and the understanding of the mechanism has been the basis for design principles for carbon-free operation and for optimum catalyst formulation.
Abstract: The mechanism of formation of whisker carbon has been studied over the last 30 years. It is the main route for carbon formation in steam reforming. The understanding of the mechanism has been the basis for design principles for carbon-free operation and for optimum catalyst formulation. Recent work has confirmed the importance of surface steps for carbon formation and given new ideas for promotion of the catalyst by inhibition of full dissociation of methane.


Book ChapterDOI
TL;DR: The use of molecular sieves with three-dimensional framework structures is well entrenched in areas as diverse as laundry detergents, oil refining and petrochemical industries, adsorbents, gas separations, agriculture and horticulture as discussed by the authors.
Abstract: Publisher Summary A zeolite is a crystalline aluminosilicate with a three-dimensional framework structure that forms uniformly sized pores of molecular dimensions. As the pores preferentially adsorb molecules that fit snugly inside the pores and exclude molecules that are too large, they act as sieves on a molecular scale. Thus, zeolites are a subset of molecular sieves. They consist of robust, crystalline silica (SiO 2 ) frameworks. At some places in the framework, AI 3+ has replaced Si 4+ and the framework carries a negative charge. Loosely held cations that sit within the cavities preserve the electro neutrality of the zeolite. Some of those cations are amenable to cation exchange and are able to reversibly interact with polar molecules. These properties have contributed significantly to the commercial success of zeolites. The use of molecular sieves with three-dimensional framework structures is well entrenched in areas as diverse as laundry detergents, oil refining and petrochemical industries, adsorbents, gas separations, agriculture and horticulture. Ever since the successful introduction of aluminosilicate molecular sieves (zeolites) in the late nineteen fifties, zeolites and the more recently discovered (silico) aluminophosphate molecular sieves have continuously improved current application areas and generated new ones.


Book ChapterDOI
Ferdi Schüth1
TL;DR: In this paper, the authors cover the discoveries which have expanded the scope of research in this field and try to give an outlook where new developments could take place, and give an overview where new applications of these materials are on the horizon.
Abstract: Research in ordered mesoporous oxides has increased dramatically in intensity over the last years. Developments not foreseen at the time when MCM-41 and FSM-16 were discovered have taken place, and in some cases applications of these materials are on the horizon. This paper will cover the discoveries which have expanded the scope of research in this field and try to give an outlook where new developments could take place.


Book ChapterDOI
TL;DR: Lurgi's Mega-Methanol as mentioned in this paper is a new technology for converting natural gas to methanol at low cost in big amounts, which gives the opportunity to replace oil consumption by methenol - so to speak as easy-to-transport liquefied natural gas - in the petrochemical industry and in the energy and fuel industry.
Abstract: Lurgi’s Mega-Methanol is a new technology for converting natural gas to methanol at low cost in big amounts. This gives the opportunity to replace oil consumption by methanol - so to speak as easy-to-transport liquefied natural gas - in the petrochemical industry as well as in the energy and fuel industry. Two processes are briefly presented and economically assessed, one producing propylene from methanol, the other generating hydrogen.

Book ChapterDOI
Vincenzo Calemma, S. Peratello, S. Pavoni1, G. Clerici, Carlo Perego 
TL;DR: In this paper, the effect of operating conditions, such as temperature, pressure and H 2 /feed ratio, on the selectivity to middle distillate and its characteristics was investigated.
Abstract: Some aspects of the hydrocracking behaviour of a C 10 + mixture of n-paraffins on a 0.3% platinum/amorphous silica-alumina catalyst have been studied. Particularly, the effect of the operating conditions, that is temperature, pressure and H 2 /feed ratio, on the selectivity to middle distillate and its characteristics was investigated. The maximum yield achieved in middle distillate was 82-87%. The isomers content of the kerosene and the gasoil fractions increases considerably during the reaction. As a consequence the Freezing point and Pour point of kerosene and gasoil show a remarkable decrease reaching values of –50 °C and –30 °C respectively. The results indicate that the vapour-liquid equilibrium plays an important role which considerably affects several aspects of the feedstock hydroconversion.


Book ChapterDOI
TL;DR: In this paper, perovskites type oxides LaMO3 were synthesized by the citrate sol-gel method and tested as catalysts for the CO2 reforming of methane.
Abstract: 1. ABSTRACT. Perovskites type oxides LaMO3 (M = Ru, Ni, Mn) were synthesized by the citrate Sol-Gel method and tested as catalysts for the CO2 reforming of methane. The influence of Ru partial substitution for Ni in the LaRuO3 structure on the activity and selectivity performance was also investigated. The results were compared with those obtained with catalyst samples prepared by wet impregnation. The effects of parameters such as reaction temperature, space velocity, CH4/CO2 ratio and time on stream were investigated and optimized to higher yields of syngas. XRD, BET surface area, TEM-EDX, IR, XPS, TPR and H2 chemisorptions characterized all the solids. Among all the solids investigated, the LaRu0.8Ni0.2O3 precursor was the most active and selective catalyst, reaching values of 89% and 90% in methane conversion and CO selectivity respectively even after 150 hours on stream. A significant decrease in coke deposition for all the catalysts was obtained which constitutes an advantage for future developments of commercial reforming catalysts.



Book ChapterDOI
TL;DR: The main application of NMR in chemistry is based on the early observation that the transition frequency measured in the NMR spectrum of an atomic nucleus in a particular chemical or structural environment is a very sensitive probe of that environment.
Abstract: Publisher Summary Nuclear magnetic resonance (NMR) has emerged as one of the most powerful tools in investigating structure and dynamics of molecular systems in the various branches of chemistry. NMR spectroscopy relies on the fact that transitions can be induced between magnetic spin energy levels of certain atomic nuclei in a magnetic field. The main application of NMR in chemistry is based on the early observation that the transition frequency measured in the NMR spectrum of an atomic nucleus in a particular chemical or structural environment is a very sensitive probe of that environment. If the distinct “chemically shitted” transitions of nuclei of the same element residing in different surroundings can be resolved in the NMR spectrum, unique information on structure, conformation and dynamics of the system under study can be obtained. This distinction of individual resonance lines or specific line patterns for resonance atoms in chemically or structurally distinct locations defines a “high-resolution” NMR spectrum.