Design and Development of Hybrid Catalyst for Hydrogen Storage: A Demonstrative Concept using Liquid Organic Hydrogen Carriers (LOHCs)

Abstract

The urgent need to address CO2 emissions resulting from the industrial revolution has placed a strong emphasis on the reduction of greenhouse gases. As a result, hydrogen has gained significant attention as a sustainable energy carrier since the oil crisis in the 1970s. Its high gravimetric energy density and the ability to produce electricity with water as the sole byproduct make hydrogen an attractive alternative to crude oil to meet the ever-increasing energy demands. However, the widespread use of hydrogen as an energy carrier poses challenges in terms of its generation and storage. In recent years, substantial progress has been made in the field of hydrogen storage through advancements in handling hydrogen in a chemically bound form, particularly in liquid organic hydrogen carriers (LOHCs).1 These systems, if translated into technology, offer solutions for onboard vehicle fuel utilization.2 A novel hybrid catalyst combining an organometallic complex, [Ir(C2H4){p-X-C6H2-2,6-[OP(tBu)2]2}] (Ir_cat/Al2O3) [X = -H, -OMe, -F, and -OPtBu2], with Pd-Ru nanostructures on an Al2O3 support has been synthesized and characterized.3 The hybrid catalyst exhibits tandem dehydrogenation-hydrogenation catalytic activity in the case of cyclooctane-cyclooctene (COA-COE) system, thus demonstrating a proof of concept for reversible hydrogen storage. The individual components of the hybrid catalyst showed dehydrogenation and hydrogenation activities as well, in separate experiments. In addition, homogeneous and heterogeneous dehydrogenation catalysts, specifically, iridium-based catalysts [Ir(H)Cl{p-X-C6H2-2,6-[OP(tBu)2]2}], [X = -H, -OMe, -F, and -OPtBu2], have also been synthesized and were tested for the dehydrogenation of isopropanol (IPA) and cyclooctane (COA).3,4 Following the individual studies of dehydrogenation, the Pd-Ru catalytic system was evaluated for the hydrogenation of cyclooctene (COE) along with other olefins. The study was then extended to potential LOHC applications. In this regard, M/Al2O3 catalysts (M = Pt, Ir, Ni) have been synthesized. These catalysts were then tested for the reversible dehydrogenation-hydrogenation of potential LOHCs, such as the methylcyclohexane/toluene and isopropanol/acetone systems, to assess their viability for future hydrogen storage and transport applications.5 The results of these studies will be presented.