Sanjay Kumar Singh

Liquid-Phase Chemical Hydrogen Storage: Catalytic Hydrogen Generation under Ambient Conditions

There is a demand for a sufficient and sustainable energy supply. Hence, the search for applicable hydrogen storage materials is extremely important owing to the diversified merits of hydrogen energy. Lithium and sodium borohydride, ammonia borane, hydrazine, and formic acid have been extensively investigated as promising hydrogen storage materials based on their relatively high hydrogen content. Significant advances, such as hydrogen generation temperatures and reaction kinetics, have been made in the catalytic hydrolysis of aqueous lithium and sodium borohydride and ammonia borane as well as in the catalytic decomposition of hydrous hydrazine and formic acid. In this Minireview we briefly survey the research progresses in catalytic hydrogen generation from these liquid-phase chemical hydrogen storage materials.

Noble-Metal-Free Bimetallic Nanoparticle-Catalyzed Selective Hydrogen Generation from Hydrous Hydrazine for Chemical Hydrogen Storage

Noble-metal-free nickel-iron alloy nanoparticles exhibit excellent catalytic performance for the complete decomposition of hydrous hydrazine, for which the NiFe nanocatalyst, with equimolar compositions of Ni and Fe, shows 100% hydrogen selectivity in basic solution (0.5 M NaOH) at 343 K. The development of low-cost and high-performance catalysts may encourage the effective application of hydrous hydrazine as a promising hydrogen storage material.

Room-temperature hydrogen generation from hydrous hydrazine for chemical hydrogen storage.

Rhodium nanoparticles (NPs) effectively catalyze the decomposition of hydrous hydrazine to produce hydrogen under ambient reaction conditions. Rh(0) NPs with a particle size of approximately 5 nm prepared in the presence of hexadecyltrimethyl ammonium bromide show higher catalytic activity.

Complete conversion of hydrous hydrazine to hydrogen at room temperature for chemical hydrogen storage.

A synergic effect of Rh and Ni in the bimetallic Rh(4)Ni nanocatalyst (Rh/Ni ratio = 4:1) makes it possible to achieve a 100% selectivity for hydrogen generation by complete decomposition of hydrous hydrazine at room temperature. The Rh(4)Ni nanocatalysts with a particle size of approximately 3 nm were prepared by alloying Rh and Ni using a coreduction process in the presence of hexadecyltrimethyl ammonium bromide (CTAB).

Bimetallic nickel-iridium nanocatalysts for hydrogen generation by decomposition of hydrous hydrazine

Alloying Ni with Ir leads to the formation of highly active catalysts for complete decomposition of hydrous hydrazine with 100% H(2) selectivity at room temperature. Use of surfactants enhances the activity by suppressing the agglomeration of nanoparticles, but does not affect the bimetallic compositions of the nanoparticles.

Bimetallic Ni-Pt Nanocatalysts for Selective Decomposition of Hydrazine in Aqueous Solution to Hydrogen at Room Temperature for Chemical Hydrogen Storage

The design and development of alloy catalysts has been a focus of intense interest because suitable selection and control over the composition of alloy catalysts can result in greatly improved activity and selectivity, while it is unusual that the combination of two inactive metals gives a highly active catalyst. In this work, we found that Ni-Pt bimetallic nanocatalysts, with a platinum content as low as 7 mol %, prepared by the coreduction of the corresponding metal chlorides, exhibit excellent catalytic activity to the decomposition of hydrous hydrazine, producing hydrogen with a 100% selectivity at room temperature, whereas the corresponding single-component nickel and platinum counterparts are inactive for this reaction. These results provide new possibilities for searching heterometallic catalysts. The present catalyst with low noble-metal content promotes the practical use of the hydrogen-storage system based on the catalytic complete decomposition of hydrazine in aqueous solution at ambient conditions.

Room-Temperature Chemoselective Reduction of Nitro Groups Using Non-noble Metal Nanocatalysts in Water

Purely aqueous-phase chemoselective reduction of a wide range of aromatic and aliphatic nitro substrates has been performed in the presence of inexpensive Ni- and Co-based nanoparticle catalysts using hydrazine hydrate as a reducing agent at room temperature. Along with the observed high conversions and selectivities, the studied nanoparticle catalysts also exhibit a high tolerance to other highly reducible groups present in the nitro substrates. The development of these potential chemoselective reduction catalysts also provides a facile route for the synthesis of other industrially important fine chemicals or biologically important compounds, where other highly reducible groups are present in close proximity to the targeted nitro groups.

Multifaceted half-sandwich arene–ruthenium complexes: interactions with biomolecules, photoactivation, and multinuclearity approach

Biological properties of the arene–ruthenium complexes have attracted substantial current interest. Their activity is appreciably defined and controlled by the arene moieties, organic ligands and the metal center. In this review, we discuss the interaction of arene–ruthenium complexes with significant biomolecular targets (DNA and enzymes). Principally, active complexes may interact with the biomolecular targets DNA or nucleobases either by direct coordination facilitated by aquation of the complex or by intercalation/stacking of the pendant planar part of the complex, usually from the planar ancillary ligands or arenes with extended rings, between the DNA base pairs. On the other hand, kinetically inert metal complexes can also provide a potential tool (as enzyme inhibitors) for the targeting of important biomolecules (other than DNA), such as protein kinases. At the same time, coordination with a metal facilitates the outreach of the organic molecules in the intracellular region. This review also highlights the photodriven activation of arene–ruthenium complexes, important metal–drug interactions and the potential of multinuclear scaffolds as important drug candidates (e.g., metallodendrimers) and drug carriers (e.g. metallacages) for targeted delivery and activity.

Nanocatalysts for hydrogen generation from hydrazine

Hydrogen is an key future fuel of interest because it is considered as an efficient energy carrier, like electricity, releasing only water when combining with oxygen (e.g. in a fuel cell) and therefore has no negative impact on the environment. Unfortunately we are not yet able to clear the economical and engineering hurdles to store hydrogen safely and efficiently. To overcome this, onboard hydrogen generation by hydrogen storage materials comes out to be an attractive and effective approach. Therefore, the concept of onboard hydrogen generation and use based on our requirements are gaining interest, reflected by a huge number of hydrogen storage materials with high hydrogen contents. Among them, hydrous hydrazine, which is a liquid and has a hydrogen content for hydrogen release as high as 8.0 wt%, proves to be a strong candidate for onboard hydrogen generation at ambient conditions. Nanoparticle catalysts (nanocatalysts) play a significant role to control the selective generation of hydrogen from catalytic decomposition of hydrous hydrazine. Nanocatalysts based on monometallic or two-component alloy catalysts involving noble (Ru, Rh, Pt, Pd, Ir) and non-noble metals (Fe, Co, Ni, Cu) and various non-metals have been extensively studied. Screening of a vast range of nanocatalysts thus provides a library of active and selective catalysts. The structure and activity of nanocatalysts are discussed focusing on the structure–activity relationship for selective hydrogen generation from hydrous hydrazine.

Catalytic transformation of bio-derived furans to valuable ketoacids and diketones by water-soluble ruthenium catalysts

Bio-derived furans such as 2-furfural (furfural), 5-hydroxymethyl-2-furfural (5-HMF) and 5-methyl-2-furfural (5-MF) were successfully transformed to a ketoacid, levulinic acid (LA), and diketones, 1-hydroxyhexane-2,5-dione (1-HHD), 3-hydroxyhexane-2,5-dione (3-HHD) and hexane-2,5-dione (HD), under moderate reaction conditions using water soluble and recyclable 8-aminoquinoline coordinated arene–ruthenium(II) complexes. Under the optimized reaction conditions using 1 mol% catalyst in the presence of 12 equivalents of formic acid at 80–100 °C, complete conversion of furfural to LA with high selectivity was achieved. Several experiments along with 1H NMR spectral studies are described which provide more insights into the mechanism underlying the transformation of furans to open ring components. Experiments performed using structural analogues of the active catalyst inferred a structure–activity relationship for the observed superior catalytic activity of the 8-aminoquinoline coordinated arene–ruthenium(II) complex. Furthermore, due to the high aqueous solubility of the studied complexes, high recyclability, up to 4 catalytic runs, was achieved without any significant loss of activity. Molecular identities of the studied 8-aminoquinoline coordinated arene–ruthenium(II) complex were also confirmed using single-crystal X-ray diffraction studies.