Download or read book Synthesis and Characterization of Atomically Dispersed Vanadosilicate Catalysts in SiO20 based Building Block Solids written by and published by . This book was released on 2007 with total page 338 pages. Available in PDF, EPUB and Kindle. Book excerpt: Silica supported vanadium complexes have attracted interest as catalysts for a variety of catalytic reactions in the past two decades. Although many strategies have been developed for incorporating vanadyl species on silica surfaces, controlling dispersion and loading while simultaneously producing single site catalysts remains a challenging goal in this context and in catalysis as well. A simple strategy for producing single-site and site-isolated vanadyl species has been explored which allows for control of both the connectivity to the support as well as the local surface structure around a V=O group. The main elements of this strategy involve construction of the support from silicate building blocks linked by groups that both hold the matrix together and act as catalytically active sites. Controlled sequential dosing lead to catalysts in which control of the identity of the sites, their connectivity to the support and dispersion is maintained. The specific system that will be described involves the controlled reaction of vanadyl chloride (VOCl3) and vanadium tetrachloride (VCl4) with the tin functionallized spherosilicate cube, (SnMe3)SiO20. Labeled 17O (SnMe3*O)8Si8O12 and (Cl3Si)8Si8O20 molecule have also been synthesized successfully by using totally new synthetic methodologies. The physico-chemical properties of these vanadium catalysts were characterized by solid state 51V and 17O NMR, gravimetric analysis, EXAFS, and atomic absorption spectroscopy. A quick survey of isopropanol dehydration and dehydrogenation with these vanadium (IV and V) catalysts has been studies. The acid-base property of these single-site and site-isolated catalysts has been assessed by the conversion of isopropanol. Preliminary results of highly selectivity (>97%) of isopropanol conversion to propene will be described.

Download or read book The Synthesis and Characterization of Novel Group 13 Nanostructured Building Block Heterogeneous Silicate Catalysts written by Joshua Garth Abbott and published by . This book was released on 2012 with total page 297 pages. Available in PDF, EPUB and Kindle. Book excerpt: A building block approach and sequential addition methodology was utilized to prepare heterogeneous silicate catalysts containing atomically dispersed group 13 metal (B, Al, Ga) centers. The octa(trimethyltin) silsequioxane, SiO12(OSnMe3), was used as the building block for the synthesis of these materials. Reaction of the building block with a variety of group 13 metal chlorides led to the formation of cross-linked matrices. All prepared materials were characterized by gravimetric analysis, gas absorption, IR, and NMR. In addition, aluminum and boron samples where characterized by 27Al and 11B solid state NMR, and gallium samples were studied using x-ray absorption techniques. Studies found the nature of the reaction for the aluminum and gallium species to be more complex than expected. This was manifested most prominently in the formation of tetramethyltin, Me4Sn, an unexpected byproduct that led to unpredictably high connectivity of the metal centers to the silicate matrix. This in turn gave rise to questions regarding the true structural nature of the metal sites. Characterization of the aluminum systems indicated that multiple types of aluminum sites (4, 5 and 6 coordinate) were present in the matrix. Increased coordination was found to result in part from the in situ formation and reaction of the [Me3Sn][AlCl4] species. It was determined that the trimethyltin cation in this ionic species was responsible for formation of Me4Sn through abstraction of a methyl group from unreacted -OSnMe3 groups remaining on the corners of the silicate building block. While the gallium analogues showed similar behavior, XANES and EXAFS analyses showed that in nearly every material, gallium had achieved 4-coordinate tetrahedral geometry. The boron systems behave quite differently than Al and Ga, producing no secondary byproduct, and forming stable 3-coordinate trigonal geometries Pyridine adsorption studies showed that these trigonal species could at least in part be converted back and forth to pseudo tetrahedral structures.

Download or read book The Synthesis and Characterization of Building Block based Titanosilicates and Their Activity Toward Alcohol Dehydration dehydrogenation Reactions written by and published by . This book was released on 2009 with total page 202 pages. Available in PDF, EPUB and Kindle. Book excerpt: Catalysis, in general, plays an integral part to many aspects of everyday life. Next-generation heterogeneous catalysts need well defined site structures to correlate with activity in order to maximize selectivity and activity. The building block methodology is a widely-applicable route to synthesizing single-site catalysts that are atomically dispersed. The building block methodology has been used to synthesize a series of titanosilicates with different site structures that mimic the potential sites in current titanosilicates. These catalysts have been characterized via EXAFS and gravimetric analysis. The EXAFS suggest single-site nature for the embedded (TiO4) and surface (ClTiO3) titanosilicate and suggest composite structure for the two intermediate titanosilicates ClTiO3 and Cl2TiO2. An embedded tripodal titanosilicate ([superscript i]PrO)TiO3 was synthesized as well to mimic the tripodal sites without the presence of chloride ligands. Alcohol dehydration/dehydrogenation reactions have been used to characterize the acidity and basicity of heterogeneous catalysts. Isopropanol and ethanol were used to characterize the embedded TiO4 and embedded tripodal ([superscript i]PrO)TiO3 building block titanosilicates as well as the embedded building block vanadium(V)-silicate and vanadium(IV)-silicate. The catalysts were highly selective toward isopropanol dehydration with the post-calcination catalysts exhibiting higher conversion at lower temperatures than the pre-calcination catalysts. The titanosilicates exhibited no selectivity toward ethanol decomposition reactions while the vanadium-silicates were more selective toward ethylene production. The differences in reactivity and selectivity illustrate the differences in the type of site and metal used.

Download or read book Metropolitan Regions Planning and Governance written by Karsten Zimmermann and published by Springer Nature. This book was released on 2019-10-24 with total page 270 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this book is to investigate contemporary processes of metropolitan change and approaches to planning and governing metropolitan regions. To do so, it focuses on four central tenets of metropolitan change in terms of planning and governance: institutional approaches, policy mobilities, spatial imaginaries, and planning styles. The book’s main contribution lies in providing readers with a new conceptual and analytical framework for researching contemporary dynamics in metropolitan regions. It will chiefly benefit researchers and students in planning, urban studies, policy and governance studies, especially those interested in metropolitan regions. The relentless pace of urban change in globalization poses fundamental questions about how to best plan and govern 21st-century metropolitan regions. The problem for metropolitan regions—especially for those with policy and decision-making responsibilities—is a growing recognition that these spaces are typically reliant on inadequate urban-economic infrastructure and fragmented planning and governance arrangements. Moreover, as the demand for more ‘appropriate’—i.e., more flexible, networked and smart—forms of planning and governance increases, new expressions of territorial cooperation and conflict are emerging around issues and agendas of (de-)growth, infrastructure expansion, and the collective provision of services.