Abstract
Formic acid (FA) possesses a high volumetric concentration of H2 (53 g L−1). Moreover, it can be easily prepared, stored, and transported. Therefore, FA stands out as a potential liquid organic hydrogen carrier (LOHC), which allows storage and transportation of hydrogen in a safe way. The dehydrogenation to produce H2 and CO2 competes with its dehydration to give CO and H2O. For this reason, research on selective catalytic FA dehydrogenation has gained attention in recent years. Several examples of highly active homogenous catalysts based on precious metals effective for the selective dehydrogenation of FA have been reported. Among them are the binuclear iridium-bipyridine catalysts described by Fujita and Himeda et al. (TOF = 228,000 h−1) and the cationic species [IrClCp*(2,2′-bi-2-imidazoline)]Cl (TOF = 487,500 h−1). However, examples of catalytic systems effective for the solventless dehydrogenation of FA, which is of great interest since it allows to reduce the reaction volume and avoids the use of organic solvents that could damage the fuel cell, are scarce. In this context, the development of transition metal catalysts based on cheap and easily available nonprecious metals is a subject of great interest. This work contains a summary on the state of the art of catalytic dehydrogenation of FA in homogeneous phase, together with an account of the catalytic systems based on non-precious metals so far reported.
Highlights
Platinum group metals (PGMs) have played a critical role in the development of modern homogeneous catalysis, shaping the landscape of catalyzed industrial processes, from bulk to commodity chemicals
Despite the unquestionable success of PGM-based catalysts, research on catalysts based on Earth-abundant metals (EAM) has received great interest in recent times
This renaissance of EAM-based catalysis is mainly due to concerns over sustainability, as they seem a better option than their PGM analogues owing to their global availability, low cost, and relatively low toxicity and environmental impact [1]
Summary
Platinum group metals (PGMs) have played a critical role in the development of modern homogeneous catalysis, shaping the landscape of catalyzed industrial processes, from bulk to commodity chemicals. The large scale required for the implementation of global energy transformations has prompted the scientific community to aim at the development of catalysts based on abundant metals for these types of reactions. In this context, formic acid (FA) has been proposed as a promising hydrogen carrier because of several key properties. Up to the present time, many efforts have been devoted to the development of homogeneous catalysts for formic acid dehydrogenation (FADH) based on PGM metals; their EAM counterparts have been less explored— remarkable advances have been reported in recent times. We would like to answer important questions regarding catalyst design, such as, are bifunctional catalysts essential to promote FADH by EAM? Or do participative ligands enhance the catalytic activity of EAM-complexes?
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