Alternative energy sources have been investigated for utilization in various applications to mitigate carbon dioxide emissions. The transportation sector is one of the major sectors that require the adaptation of renewable energy storage technologies for onboard applications. Formic acid is a liquid energy carrier that has the potential of replacing current fuels and mitigating carbon dioxide emissions through a circular carbon economy. The production of energy from formic acid can be achieved by homogenous catalysis to extract hydrogen from formic acid. The most promising metals for formic acid dehydrogenation in aqueous solution have been mainly ruthenium and iridium. While iridium has mostly surpassed ruthenium, further exploration of ruthenium is necessary because it is more economical. This work presents the synthesis and catalytic performance of a N,N-bidentate Ru(II) complex. X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and Mass spectrometry (MS) were used to confirm the structure of the catalyst. The title complex was found to be an efficient system for formic acid dehydrogenation to hydrogen gas and carbon dioxide in the aqueous phase. The highest TOF achieved is 656 h-1 in the presence of two equivalents of sodium formate to formic acid in water at 90 °C. There was no detection of carbon monoxide throughout the reaction process, suggesting the high selectivity of this catalytic system.

Formic acid (FA) has been considered as one of the most promising materials for hydrogen storage today. The catalytic decarboxylation of formic acid ideally leads to the formation of CO2 and H2, and such CO2/H2 mixtures can be successfully applied in fuel cells. A large number of transition-metal based homogeneous catalysts with high activity and selectivity have been reported for the formic acid decarboxylation. In this presentation, we report ruthenium and rhodium complexes containing an N, N′-diimine ligand for the selective decomposition of formic acid to H2 and CO2 in water in the absence of any organic additives. Among them, the Ru complex could provide a TOF (turnover frequency) of 12 000 h–1 and a TON (turnover number) of 350 000 at 90 °C in the HCOOH/HCOONa aqueous solution. In addition to that, efficient production of high-pressure H2 and CO2 (24.0 MPa (3480 psi)) was achieved through the decomposition of formic acid with no formation of CO by this Ru complex. Moreover, well-defined ruthenium (II) PN3P pincer complexes were also developed for the reversible reaction-hydrogenation of carbon dioxide. Excellent product selectivity and catalytic activity with TOF and TON up to 13,000 h-1 and 33,000, respectively, in a THF/H2O biphasic system were achieved. Notably, effective conversion of carbon dioxide from the air into formate was conducted in the presence of an amine, allowing easy product separation and catalyst recycling.

Heterogeneous catalysts form a highly important part of everyday life, ranging from the production of fertiliser enabling the growth of crops that sustain much of the world's population to the production of synthetic fuels. They constitute a key part of the chemical industry and contribute towards substantial economic and environmental benefits. Heterogeneous catalysts are also believed to have an important role to play in a future hydrogen economy, reducing our requirements for fossil fuels. To this end, formic acid has been proposed as a potential hydrogen storage material for small portable devices. Additionally, formic acid has historically been used as a probe molecule to study catalyst materials and recent developments in the knowledge of its decomposition pathways and the preferred sites of these reactions, establish a good foundation for further study. This work explores a range of novel modification techniques that alter the activity of Pd nanoparticles to decompose formic acid to H₂ and CO₂. The methods used are the addition of polymers, attaching various functional groups to the surface of the catalyst support and decoration of nanoparticles with sub-monolayer coverages of another metal. Using a range of characterisation methods including FTIR of an adsorbed CO probe, XRD and XPS coupled with computational modelling, it is found that these methods result in some significant electronic and/or geometric alterations to the Pd nanoparticles. For polymer modification, the nature of the pendent group is highly important in determining the effects of the polymer on the Pd particles, with all the tested polymers resulting in varying degrees of electronic donation to the Pd surface. The geometric modifications caused by the polymers also varied with pendent groups; with amine containing pendent groups found to selectively block low coordinate sites, preventing the undesired dehydration of formic acid which results in poisoning of the Pd catalyst by the resulting CO. Attachment of amine groups to the surface of metal oxide catalyst supports, is demonstrated to result in dramatic electronic promotional effects to the supported Pd nanoparticles, and when an amine polymer is attached to the support surface the geometric modification is again observed. Finally decoration of Pd nanoparticles with a sub-monolayer coverage of a second metal is examined, resulting in some similar electronic and geometric effects on Pd nanoparticle surfaces to those observed with polymer modification with corresponding changes in formic acid decomposition activity. Overall, a number of methods are displayed to tune the catalytic activity and selectivity of Pd nanoparticles for formic acid decomposition, resulting in catalysts with some of the highest reported TOF's at room temperature. These modification methods are believed to be potentially applicable to a wide range of other catalytic reactions that operate under mild conditions.