1,720,959 research outputs found
Design and Synthesis of Immobilized Iridium Complexes and Their Catalytic Application in Neat Formic Acid Dehydrogenation
No full textThe main target of this thesis is to synthesize, investigate, and explore the chemistry and reactivity of immobilized catalysts. The focus will be on iridium complexes as well-defined catalysts for developing selective heterogeneous catalysts.
Chapter 1 provides a comprehensive overview of catalysis, introducing the different immobilization techniques. We elaborate on surface organometallic chemistry (SOMC) and discuss preparation and reactivity. This chapter also introduces formic acid dehydrogenation and discusses the preparation and reactivity of selected examples of immobilized catalysts.
Chapter 2 discusses a detailed analysis and comparison of the catalytic activities of the surface organometallic immobilized catalyst and its homogenous precursor, the Ir-PN3P pincer complex. The immobilized catalytic system uses the novel modified silica support, which includes tetra-coordinated aluminum hydride moiety. The catalytic study focuses on neat formic acid dehydrogenation in a solvent-free environment and utilizes cesium formate as a basic additive that could also serve as a reaction medium. Our findings indicate a significant activity enhancement and longer lifetime in the case of the Ir immobilized catalyst, which can be attributed to the surface rigidity creating an isolated site and preventing undesired bimolecular deactivation.
Chapter 3 encompasses the synthesis and characterization of the immobilized picolinamide iridium complex. Our work evaluates the amine linkage effect by employing an N, N`-bidentate picolinamide iridium complex supported onto aluminum hydride-modified silica support. We explore using solid bases as additives in a solvent-free reaction medium and avoid using volatile bases to assess the feasibility of neat formic acid dehydrogenation. Our findings reveal that the Immobilized bidentate picolinamide iridium system achieves a high TOF of 40,000 h-1, comparable to its homogenous analog.
Chapter 4 deals with immobilizing an iridium picolinamide complex onto hierarchically ordered zeolite (ZAK-1700) exhibiting a 3D-cubic framework. We investigate the changes in the coordination sites around the surface fragment upon utilizing zeolite and the impact on the reactivity. We evaluate the reactivity in a neat formic acid dehydrogenation process, using solid bases as additives. The immobilized catalyst achieves a high TOF of 70,000 h-1. A significant improvement compared to its iridium picolinamide homogenous analog, which demonstrates a TOF of 45,000 h-1. Furthermore, the optimized catalytic performance test of the immobilized catalyst is conducted under solvent-free/neat conditions, and a TON of 29,000 is recorded when sodium formate is employed.
Finally, the last chapter presents the thesis conclusion. The future outlook discusses ongoing applications related to immobilized catalytic systems, highlighting potential advancements and new research directions
Titanium Neopentyl supported on KCC-1 and Al-modified KCC-1 and its Catalytic Application for Ethylene polymerization
No full textA new generation of Titanium based catalysts for ethylene polymerization has been
developed through the Surface Organometallic Chemistry (SOMC) methodology using a
novel type of silica support having a 3D fibrous morphology, KCC-1. The first type of Tibased
catalyst was obtained by reacting isolated silanol surface groups, ≡SiOH of KCC-1
(dehydroxylated at 700 ⁰C under high vacuum, 10-5 bar) with titanium (IV) tetraneopentyl,
Ti(CH2tBu)4 to produce [(≡SiO)Ti(CH2tBu)3]. The second type of Ti-based catalyst was
generated by using an Al-modified KCC-1. The peculiarity of this support is due to the
presence of tetra-coordinated aluminum-bound hydroxyl group, [(≡Si-O-Si≡)(≡SiO)2Al-
OH] that can be used as a Lewis Acid anchor sites and generate new catalytic properties.
The well-defined [(≡Si-O-Si≡)(≡SiO)2Al-OH] was obtained by reacting diisopropylaluminum
hydride with KCC treated at 700 °C followed by a thermal treatment
at 400 °C and oxidation with N2O. IR spectra of pyridine adsorbed on the Al sites show
that these were strong Lewis acid sites (constituting 80% of the total Al sites). Thus, the
highly electrophilic support surface was used to create a single well-defined surface
organo-titanium fragment [(≡Si–O–Si≡)(≡Si–O–)2Al–O–Ti(CH2tBu)3] by the reaction of
the surface [(≡Si–O–Si≡)(≡Si–O)2Al–OH]) groups with Ti(CH2-tBu)4 at room temperature
for 4 h in dry pentane.
The performance of each Ti-supported catalyst assessed for ethylene polymerization. It
was found that Al-modified support (highly electrophilic) provide better activity
compared to the unmodified one. Indeed, the productivity of the catalyst [(≡Si–O–
Si≡)(≡Si–O–)2Al–O–Ti(CH2tBu)3] was found to be 67.8 g of PE/ 1mmol Ti/ 1h with
molecular weight of 3208408 g/mol; polydispersity was found to be 2.3, and (HDPE)
high-density polyethylene was obtained. In contrast, [(≡SiO)Ti(CH2tBu)3] (unmodified
one) produces lower molecular weight polymer 989843 g/mol, higher polydispersity (PD)
6.7 and low-density polyethylene (LDPE) productivity was found to be 14.670 g
PE/1mmol Ti /1h. These results demonstrate that modification of the oxide ligands on
silica through a generation of Al Lewis acid site opens up new catalytic properties,
markedly enhancing the catalytic performance of supported organotitanium species.
We also demonstrate how the silica mesostructure (2D vs 3D ) affects the catalytic
activity in ethylene polymerization. While SBA15 (2D) could limit the accessibility of
the active sites resulting in lower yield. In contrast, KCC-1 (3D) are more active in
ethylene polymerization, because the active sites reside on the external surface are fully
accessible to the substrate
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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