Mesoporous silica beads encapsulated with functionalized palladium nanocrystallites: Novel catalyst for selective hydrog
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2-(3,4 epoxycyclohexyl)ethyltrimethoxysilane (EETMS)/3-glycidoxypropyltrimethoxysilane (GPTMS) mediated, in situ synthesis of functional palladium (Pd) nanocomposites over the graphene oxide (GO) surface is reported. The prepared nanocomposites viz, Pd/EETMS, Pd/GPTMS, Pd/GO/ EETMS, and Pd/GO/GPTMS, are encapsulated into mesoporous (2–10 nm) silica-alginate beads to primarily serve the development of cost-effective catalyst for on-board generation of hydrogen. Major findings involve: (i) the synthesis of porous silica alginate beads, with the controlled pore sizes (2–10 nm) as a function of concentration of alkoxysilanes, (ii) onboard release of hydrogen from the decomposition of hydrazine, which is evaluated as: (1) time-dependent disappearance of the N–N bond stretching band at 1069 cm 1 based on the FTIR spectroscopy, (2) volumetric estimation of the equimolar hydrogen using methylene blue (MB); (3) catalytic reduction of p-nitroaniline (PNA). The decomposition of high concentration of hydrazine is made possible using very low concentration of palladium. On calcination the efficiency of catalysts found to enhance further. The noteworthy finding is probing the hydrogen evolution using FTIR spectroscopy. Hydrogen selectivity of ;100% is obtained from the most efficient catalyst (Pd/GO/EETMS-623 K).
I. INTRODUCTION
Hydrogen is considered a requisite energy source for future perspectives, as it is a clean and inexhaustible fuel.1– 3 Besides having an edge over nonrenewable energy resources, efficient storage and utilization of hydrogen is still a challenging task. Recently various technological innovations are done to store the hydrogen energy.4 Hydrous hydrazine (N2H4) which consists of nearly 8.0 wt% of hydrogen, is liquid over a wide range of temperature (298–343 K) and less vulnerable to explosion, therefore, it is considered a promising material for chemical hydrogen storage and transportation.5,6 Efficient and selective catalysts are required for on-board generation of hydrogen gas from hydrazine. Catalyst reinforced liberation of hydrogen on the decomposition of hydrazine7,8 is one of the recent major findings. A number of catalysts have been fabricated for the decomposition of hydrazine till date, among them nanoscaled supported catalysts [FeNi/Cu, Ni (100), Ir-MWNTs], nanoparticle catalysts [Pt–Ni (111), Rh (0), Pt (111)] have gained much attention.9–13 Although these catalysts have been reported to attain 100% H2 selectivity but almost in every case, decomposition occurred at higher temperature.14,15 GObased noble metal nanohybrids16–18 are helpful in facilitating the dispersibility and electron transfer related issues. Contributing Editor: Xiaobo Chen a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.226
The direct growth of nanoparticles over the surface and at the active sites of graphene oxide (GO) prevents the aggregation of nanocrystals and controls the nano geometry.16–18 However, despite the high catalytic potential of GO based noble metal catalysts,
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