Platinum catalysts for the sustainable oxidation of biomass related compounds

Abstract

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.

Date of Award	2020
Original language	English
Supervisor	Marta Granollers Mesa (Supervisor) & Georgios Kyriakou (Supervisor)