Infoscience

Thesis

Homogeneous catalytic decomposition of formic acid for high pressure hydrogen generation

The main obstacles in the widespread use of hydrogen as energetic alternative to fossil fuels are storage problems intrinsically linked to its extremely light and explosive nature. Since no ideal storage systems currently exist, reversible fixation of hydrogen is a very active field of research. Formic acid has previously been proposed as hydrogen storage material using heterogeneous catalysts to decompose it. These systems, however, lose activity over time and/or have low selectivity. Formic acid decomposition has been revisited during the course of this thesis in attempt to provide a catalytic system that efficiently and selectively decomposes formic acid into H2 and CO2. Accordingly, a homogeneous catalytic system to decompose formic acid in aqueous phase has been developed. The catalytically active species are formed in situ from [Ru(H2O)6]2+ or RuCl3, and sulfonated phosphine ligands. The decomposition takes place under mild conditions, over a large range of temperatures (25-170°C) and pressures (1-750 bar, at least). The robustness of the catalytic systems allows a very large number of catalytic runs to be performed without any deactivation, hence, continuous hydrogen production could be achieved. Mechanistic investigations allowed the characterisation of several intermediates and a catalytic cycle has been proposed. The selective catalytic process developed affords hydrogen essentially free of CO, at desired rates and pressures, overcoming previous limitations in the use of formic acid as a hydrogen storage material. The research undertaken in this thesis is presented in three parts: (i) development and optimisation of the catalytic system in batch mode, (ii) mechanistic investigations on the optimised catalysts, and (iii) development of a continuous hydrogen production system.

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