Heterogeneous catalysis basic zeolite

Theoretical and Experimental NMR techniques provide powerful tools for the investigation of heterogeneous catalysis. Recent advances in in situ NMR techniques are summarized, as are advances in theoretical methods. The utility of our combined theoretical/experimental approach is illustrated by studies of the pentamethylbenzenium cation and the 1,3-dimethylcyclopentenyl cation in zeolite HZSM-5, acetylene adsorption on MgO, and the isopropyl cation on frozen SbF5. We also discuss the role of the basicity of adsorbates in the formation of stable carbenium ions on zeolites. 

Owing to the great interest in the argument, minireviews have been published on the use of solid catalysts in Friedel-Crafts acylation. Kouwen-hoven and van Bekkum, in a chapter of the Handbook of Heterogeneous Catalysis, faced the basic problem of the use of zeolites in the reaction. A further essential overview of the same argument was reported by Metivier in Fine Chemicals through Heterogeneous Catalysis Furthermore, Bezouhanova described the synthetic aspects of the zeolite-catalyzed preparation of aromatic ketones. ... 

Conna, A Garcia, H Leyva, A Primo. A. Basic zeolites containing palladium as bifunctional heterogeneous catalysts for the Heck reaction. Applied Catalysis A General, 2003 247,41 -49. 

We extend our imderstanding of the concepts of chemical bonding and reactivity learned in Chapter 3 on metals and Chapter 4 on zeolites to catalysis over metal oxides and metal sulfides in Chapter 5. The featmes that lead to the generation of surface acidity and basicity are described via simple electrostatic bonding theory concepts that were initially introduced by Pauling. The acidity of the material and its application to heterogeneous catalysis are sensitive to the presence of water or other protic solvents. We explicitly examine the effects of the reaction medium in which the reaction is carried out. In addition, we compare and contrast the differences between liquid and solid acids. We subsequently describe the influence of covalent contributions to the bonding in oxides and transition to a discussion on the factors that control selective oxidation. 

Adsorption microcalorimetry is the measure of the heat of adsorption evolved when dosing measured small amounts of a vapor probe on a surface. Cardona-Martinez and Dumesic [36] summarized the results obtained for oxides, zeolite, and metal catalysts before 1992. Summaries of the application of these techniques to gas-solid interactions and heterogeneous catalysis have been published recently [37-39]. As done by Auroux and Gervasini [40] for a number of binary metal oxides, calorimetric studies of the acidity and basicity are mostly performed using ammonia as an acidity probe and carbon dioxide as a basicity probe [41]. 

In this communication a study of the catalytic behavior of the immobilized Rhizomucor miehei lipase in the transesterification reaction to biodiesel production has been reported. The main drawbacks associated to the current biodiesel production by basic homogeneous catalysis could be overcome by using immobilized lipases. Immobilization by adsorption and entrapment have been used as methods to prepare the heterogeneous biocatalyst. Zeolites and related materials have been used as inorganic lipase supports. To promote the enzyme adsorption, the surface of the supports have been functionalized by synthesis procedures or by post-treatments. While, the enzyme entrapping procedure has been carried out by sol-gel method in order to obtain the biocatalyst protected by a mesoporous matrix and to reduce its leaching after several catalytic uses. 

Most of the adsorbents used in the adsorption process are also useful to catalysis, because they can act as solid catalysts or their supports. The basic function of catalyst supports, usually porous adsorbents, is to keep the catalytically active phase in a highly dispersed state. It is obvious that the methods of preparation and characterization of adsorbents and catalysts are very similar or identical. The physical structure of catalysts is investigated by means of both adsorption methods and various instrumental techniques derived for estimating their porosity and surface area. Factors such as surface area, distribution of pore volumes, pore sizes, stability, and mechanical properties of materials used are also very important in both processes—adsorption and catalysis. Activated carbons, silica, and alumina species as well as natural amorphous aluminosilicates and zeolites are widely used as either catalyst supports or heterogeneous catalysts. From the above, the following conclusions can be easily drawn (Dabrowski, 2001) ... 

Volume 4 is dedicated to three important topics Catalysis (Part 4.1), Heterogeneous Systems (Part 4.2), and Gas Phase Systems (Part 4.3). The six chapters of Part 4.1 cover the most important aspects of electron transfer catalysis, from fundamental concepts to organic synthesis, from carbon dioxide fixation to protein catalysis, from redox modulation to biomimetic catalysis. Part 4.2 deals with the basic aspects and the latest developments in electron transfer on semiconductors, dye-sensitized electrodes, mono- and multilayers, intercalated compounds, zeolites, micelles and related systems. Part 4.3 covers gas phase systems, from atoms to small molecules, exciplexes, and supermolecules. 

Heterogeneous catalysts which are active for the catalysis of the MPVO reactions include amorphous metal oxides and zeolites. Their activity is related to their surface basicity or Lewis acidity. Zeolites are only recently being developed as catalysts in the MPVO reactions. Their potential is related to the possibility of shape-selectivity as illustrated by an example showing absolute stereoselectivity as a result of restricted transition-state selectivity. In case of alkali or alkaline earth exchanged zeolites with a high aluminium content (X-type) the catalytic activity is most likely related to basic properties. For zeolite BEA (Si/Al=12), however, the dynamic character of those aluminium atoms which are only partially connected to the framework appear to play a role in the catalytic activity. Similarly, the Lewis acid character of the titanium atoms in aluminium free [Ti]-BEA explains its activity in the MPVO reactions. 

The use of nitromethane as a probe of basicity of zeolites (NaX, CsX, CsX 9Cs) and mixed oxides, Mg(Al)0, is discussed. Various species (physisorbed nitromethane, aci-anion nitromethane, and methazonate salt analogue) formed upon nitromethane adsorption were characterized by C MAS NMR spectroscopy. Heterogeneous base catalysis of the Michael addition of nitromethane on cyclohex-2-en-1-one was also studied. Low rates were obtained for catalysts showing only nitromethane physisorption. Formation of aci-anion nitromethane was observed for solids of medium efficiency correlation of the chemical shift with the initial rate was established. Finally, the decrease of Lewis acidity and concomitant increase of basicity led to methazonate formation and to the more efficient catalysts. 

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