Data di Pubblicazione:
2015
Citazione:
NOVEL APPROACHES TOWARDS THE OPTIMISATION OF METAL NANOPARTICLE BASED CATALYSTS / S. Campisi ; tutor: L. Prati; cotutor: A. Villa. DIPARTIMENTO DI CHIMICA, 2015 Dec 02. 28. ciclo, Anno Accademico 2015. [10.13130/campisi-sebastiano_phd2015-12-02].
Abstract:
The main goal of my Ph.D. project has been the development of novel approaches for the optimisation of supported noble metal nanoparticles, which are well-established catalysts for liquid phase oxidation reactions.
The partial oxidation of oxygen-containing compounds (alcohols, aldehydes, carbohydrates) is a profitable process, the corresponding products (aldehydes, ketones, epoxides, carboxylic acids, esters and lactones) being key intermediates in the synthesis of fine chemicals and commodity. In the perspective of biomass valorisation these processes are recently assuming an increasing relevance. Indeed, many biomass-derived platform molecules contain oxidizable functional groups and therefore can be easily converted in value-added compounds by oxidation.
The oxidation of organic compounds can be carried out in the gas phase through continuous-flow reactors using air or oxygen as oxidant. Nevertheless, these processes require high temperatures and their application is restricted to volatile and thermally stable reactants and products. From this point of view working in the liquid phase seems to be more suitable for energy saving, since milder conditions can be adopted, compared to gas phase. The main drawback of the current industrial technologies for liquid phase oxidation processes is the use of stoichiometric inorganic oxidants, such as dichromate and permanganate, which are toxic and corrosive. The employment of these reactants therefore entails environmental issues (production of high volumes of toxic wastes), handling difficulties and reactor maintenance problems (corrosion, plating out on reactor walls). According to green chemistry principles, the replacement of toxic stoichiometric processes with catalytic and environmentally benign routes is then heartily recommended.
Noble metal unsupported and supported nanoparticles have been extensively explored as heterogeneous catalysts for the liquid phase oxidation of oxygen-containing organic compounds in the presence of molecular oxygen, air or hydrogen peroxide as sole oxidants.
In particular platinum group metals (Pt, Pd, Ru, Rh) have shown to be able to oxidize alcohols to the corresponding carbonyl or carboxylic compounds under mild conditions (close to ambient conditions) . However, these systems rapidly undergo deactivation by over-oxidation or metal dissolution into solution (leaching). Otherwise, nano-sized gold exhibits a remarkable activity and it possesses unexpected advantages over platinum group metals in terms of selectivity control and resistance to deactivation. The strongest limitation in using gold NPs as catalysts is the compulsory use of a basic environment . Recent studies showed that alloying gold with a second metal (platinum or palladium) is possible to obtain effective catalytic systems in terms of activity, durability and selectivity even in the absence of a base. Besides the use of bi- or multimetallic systems (e.g. AuPt or AuPd), the catalytic performances are strongly affected by many factors, including the addition of promoters (e.g. Bi), the influence of support and the preparation route. A simultaneous fine tuning of all these parameters is not a straightforward task, therefore the design of catalysts is a still challenging research target. A multidisciplinary approach seems to be the better strategy for facing this challenge. In this view, the development of a catalyst should be the result of the combination of three main aspects (preparation, characterization, testing), which can be investigated on different levels (from atomic to macroscopic level) and with several tools (from in situ characterization to computational modelling).
During my Ph.D. project a similar approach has been adopted. In the first section (Chapter 2) my resea
Tipologia IRIS:
Tesi di dottorato
Keywords:
selective oxidation; heterogeneous catalyst; design of materials; glycerol
Elenco autori:
S. Campisi
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