Development of efficient molecular catalysts for hydrogen production from C-1 based liquid organic hydrogen carriers

Abstract

This chapter highlights the need to develop and popularize alternative and renewable sources of energy in the current world scenario. In this context, hydrogen energy is one of the most popular choices which needs to be produced from water or other biomass sources. The chapter particularly focuses on the background of hydrogen production from formic acid and formaldehyde with different transition metal-based catalysts reported in literature. It describes the gradual progress in the field of hydrogen production from formic acid and formaldehyde by the development of efficient catalytic systems and role of different ligands attached to the metal center in achieving enhanced catalytic activity with a particular focus on water based catalytic systems due to its importance in the sustainability of the process. Among the studied complexes, Ir based complexes prove to be very promising candidates for hydrogen production from formic acid to achieve excellent turnover numbers (TONs) and turnover frequencies (TOFs), but the very high price of iridium is drawing the attention of the researchers globally to develop cheaper yet efficient catalysts for this kind of reactions. Ruthenium based complexes along with several other non – noble metal-based catalysts prove to be promising and effective in this direction. Ligand design plays a crucial role in tuning the catalytic activities by controlling the electronic and steric environment around the metal center. Specific examples of catalytic systems active in aqueous medium along with the reaction mechanism from literature have been discussed in this chapter. Although there is a significant advancement in this field of metal catalyzed hydrogen production from C-1 based LOHCs, several challenges related to the development of efficient catalysts for water based reactions, reducing the cost of the catalytic system and identifying important reaction intermediates needs to be addressed properly. In this direction, this thesis describes the design and synthesis of several bidentate N,N/N,O donor ligand based arene-Ru(II) complexes and their catalytic activities towards hydrogen production from formic acid and formaldehyde in aqueous medium along with detailed mechanistic investigations.