Platinum catalysts for the sustainable oxidation of biomass related compounds

The project described in this thesis is concerned with the platinum catalysed aerobic oxidation of biomass related model compounds, to explore new clean catalytic routes for the production of relevant intermediates in the field of fine chemicals and materials. This work started with the optimisation of mesoporous and hierarchical TLCT SBA-15 structures through systematic variation of their textural properties, including pore diameter, surface area and metal loading. The successful synthesis has been validated via extensive characterisation of the materials. Pore-expanded mesoporous and macro-mesoporous Pt-TLCT SBA-15 materials have been subsequently applied to the aerobic oxidation of dodecanal. The attentive choice of the type of support architecture conferred significant advantages in terms of internal diffusion and catalytic activity, evidencing the elimination of mass-transport barriers inherent to SBA-15 materials. Furthermore, a green and sustainable alternative for the selective synthesis of cinnamic acid from cinnamaldehyde has been investigated, as cinnamic acid is a promising compound to be developed in the medical field. The complex reaction mechanism has been studied, to identify the optimal conditions that favour the formation of cinnamic acid while minimising the production of benzaldehyde, the main by-product of this reaction. Air as oxidative agent together with a Pt-SiO2 catalyst decreased the activity of the oxidative cleavage mechanism that promotes the formation of benzaldehyde, rendering the reaction more selective towards cinnamic acid. Finally, the aerobic oxidation of 5-hydroxymethylfurfural has been explored with platinum nanoparticles dispersed over fumed silica, a non-porous acidic support that has not been extensively investigated in previous scientific literature, to assess the importance of the solid support in this reaction. A comprehensive study to investigate the catalytic abilities of Pt-SiO2 has been conducted, exploring the effect of different temperatures, pressures and amount of base. The employed catalysts have been prepared with two platinum precursors, in order to examine if different precursors had a remarkable impact on the catalysis. The obtained results led to the conclusion that, between the two precursors used, hydrogen hexachloroplatinate (IV) hexahydrate represents the most suitable one for HMF aerobic oxidation, since it allowed smaller nanoparticle size, which in turn afforded higher platinum content located on the surface of the catalyst, where the reaction occurred

Platinum catalysed aerobic selective oxidation of cinnamaldehyde to cinnamic acid

Aerobic selective oxidation of allylic aldehydes offers an atom and energy efficient route to unsaturated carboxylic acids, however suitable heterogeneous catalysts offering high selectivity and productivity have to date proved elusive. Herein, we demonstrate the direct aerobic oxidation of cinnamaldehyde to cinnamic acid employing silica supported Pt nanoparticles under base-free, batch and continuous flow operation. Surface and bulk characterisation of four families of related Pt/silica catalysts by XRD, XPS, HRTEM, CO chemisorption and N2 porosimetry evidence surface PtO2 as the common active site for cinnamaldehyde oxidation, with a common turnover frequency of 49,000 ± 600 h−1; competing cinnamaldehyde hydrogenolysis is favoured over metallic Pt. High area mesoporous (SBA-15 or KIT-6) and macroporous-mesoporous SBA-15 silicas confer significant rate and cinnamic acid yield enhancements versus low area fumed silica, due to superior platinum dispersion. High oxygen partial pressures and continuous flow operation stabilise PtO2 active sites against in-situ reduction and concomitant deactivation, further enhancing cinnamic acid productivity

Higher Education Interdisciplinarity: Addressing the Complexity of Sustainable Energies and the Green Economy

Universities play a strategic role towards a sustainable future, as they address the complex scientific research on green transition and enable students from diverse backgrounds to acquire different skills, integrate multiple perspectives, and handle the sustainability of the ongoing and future renewable energy sector. In this paper, we describe a collaborative project between multiple HEIs (European and African) and local institutions, which promotes an interdisciplinary approach to address climate change and green energy transitions in the curricula of universities, used in the context of the ERASMUS+ program (DALILA-Development of new Academic curricuLa on sustaInabLe energies and green economy in Africa). The project recognizes and values different kinds of knowledge in renewable energy and green economy to address the energy transition in higher education in African countries as a prerequisite for climate change mitigation and sustainable development