Reversible Hydrogenation–Dehydrogenation of Acetylpyridine-Pd-MIL-101(Cr) for Chemical Hydrogen Storage

Abstract

3-Acetylpyridine (AcP), as an organic hydrogen carrier, and Pd nanoparticles, as a catalyst, were incorporated into MIL-101­(Cr) for chemical hydrogen storage. AcP was first grafted into MIL-101­(Cr), and then Pd (0.5–4.0 wt %) was encapsulated by a double-solvent adsorption process. Thermogravimetric analysis, inductively coupled plasma–optical emission spectrometry, X-ray photoelectron spectroscopy, transmission electron microscopy, in situ X-ray adsorption near-edge structure analysis, 1H nuclear magnetic resonance (NMR), and elemental analysis suggested the existence of AcP and Pd nanoparticles (NPs) inside the MIL-101­(Cr) cages. The chemical hydrogen storage of samples was evaluated by H2 temperature-programmed reaction. In situ Fourier transform infrared and 1H NMR techniques verified the hydrogenated and dehydrogenated forms of AcP upon hydrogen uptake. Reversible hydrogenation/dehydrogenation can be readily regulated by H2 partial pressure and temperature. The chemical hydrogen storage could be accomplished only when AcP and Pd NPs were adjacently present. The chemical hydrogen storage was enhanced with an increased Pd loading up to 0.33 mmol H2·g–1 per cycle. With the manipulation of hydrogenation and dehydrogenation temperatures at 150 °C, the chemical hydrogen storage can be maintained for up to 10 cycles. The material reported herein is one of the noncryogenic chemical hydrogen storages that can be operated at constant temperature and atmospheric pressure.

Elucidating Improvements to MIL‐101(Cr)’s Porosity and Particle Size Distributions based on Innovations and Fine‐Tuning in Synthesis Procedures

“…For example, Makmeesub et al synthesized (additive-free)-MIL-101(Cr) hydrothermally at 218 °C for 18 h as per other reported works [150][151][152] (S BET = 3510 -3960 m 2 g −1 ) but achieved markedly higher S BET = 4440 m 2 g −1 by thoroughly washing their sample with DMF, water, acetone, and methanol. [153] As shown in Figure 9b, there are 16 entries with V pore 2 cm 3 g −1 and above. [15,18,29,150,151,[154][155][156][157][158][159][160][161][162][163][164] Four of these samples were washed with NH 4 F despite the additive-free synthesis approach.…”

“…synthesized (additive‐free)‐MIL‐101(Cr) hydrothermally at 218 °C for 18 h as per other reported works [ 150–152 ] ( S BET = 3510 – 3960 m 2 g −1 ) but achieved markedly higher S BET = 4440 m 2 g −1 by thoroughly washing their sample with DMF, water, acetone, and methanol. [ 153 ]…”

Highly stable Pd2+ species anchoring on ethylenediamine-grafted-MIL-101(Cr) as a robust oxidation catalyst

“…47 We have also reported the incorporation of acetyl pyridine at Cr 3+ nodes in MIL-101(Cr). 32 Anchoring Pd 2+ species on ethylenediamine-grafted-MIL-101(Cr). When 0.03 mmol Pd per g was further incorporated into MIL-101(Cr), either with or without ethylenediamine (0.5-1.2 mmol g −1 ), a slight decrease in the relative XRD intensity was observed (Fig.…”

“…It would be easily manipulated as an anchoring ligand with the coordinatively unsaturated metal node of various MOFs. [27][28][29][30] Particularly, stable Cr 3+ nodes in MIL-101(Cr) are simply generated after dehydration, 31 and can readily coordinate with various N donors, e.g., acetylpyridine, 32 guanidine 33 and ethylenediamine. 34 This would open an opportunity for immobilizing Pd 2+ species that withstand reduction or decomposition at high temperatures.…”