One-step encapsulation of Pd nanoparticles in MOFs via a temperature control program

Abstract

A facile cooperative in situ metal precursor incorporation and on-site moderate reduction strategy is established for one step encapsulation of Pd nanoparticles in the pore of MOFs, which could not be achieved by a quick heating process.The control over size and location of metal nanoparticles (MNPs) within metal-organic frameworks (MOFs) is achieved in one step through a cooperative in situ incorporation of metal precursor and on-site moderate reduction process, which is operated by temperature programming control. The choice of the operation temperatures is based on the MOF assembly temperature (T1), and an elevated temperature (T2) to elicit the reducibility of DMF solvent to fabricate MNPs. Such a rational design could effectively introduce metal precursors into the pores of MOF and on-site moderately reduce the embedded metal ions to generate tiny MNPs by the penetrated DMF, which could not be achieved by a quick heating process. The proposed methodology has been successfully applied to the one-step fabrication of ultrafine Pd NPs selectively encapsulated inside the pores of UiO-67 without any external reducing agents. The obtained Pd-in-UiO-67 shows superior catalytic activity and selectivity in the hydrogenation of styrene even under room temperature and atmosphere pressure of H2.

Metal–Organic Frameworks Encapsulating Active Nanoparticles as Emerging Composites for Catalysis: Recent Progress and Perspectives

“…The obtained products were characteristic of Pd NPs of 3.2 nm in diameter homogeneously distributed inside UiO‐67(Zr) and its loading of 1 mol%. Also, Li et al reported a simple temperature control program to encapsulate Pd NPs inside UiO‐67(Zr) with its loading of 1.0 wt% . This process involved incorporation of PdCl 2 (CH 3 CN) 2 into the mixture of ZrCl 4 , 2,2′‐bipyridine‐5,5′‐dicarboxylate, DMF and HCl at 80 °C and on‐site moderate reduction process to fabricate Pd NPs at an elevated temperature of 130 °C.…”

Metal–organic framework derived Pd/ZrO2@CN as a stable catalyst for the catalytic hydrogenation of 2,3,5‐trimethylbenzoquinone

“…In contrast, for the corresponding Pd/ZrO 2 @C derived from Pd@UiO‐66(Zr) under the same conditions, a sharp diffraction peak at around 40 °C ascribed to the Pd species was clearly observed (Figures S1 and S2 in the Supporting Information), suggesting that the Pd species significantly aggregated during the thermal transformation procedure. This comparison demonstrates that amine groups are indispensable for the dispersion of ultra‐small Pd nanoclusters . Further calculations using the Scherrer equation revealed that the size of the Pd nanoparticles in Pd/ZrO 2 @C was about 13 nm.…”

“…By further pyrolysis at high temperature under an inert atmosphere, the organic linkers and inorganic Zr‐based anodes of NH 2 ‐UiO‐66(Zr) were converted into nitrogen‐doped porous carbon and ZrO 2 nanoparticles, respectively. The ‐NH 2 groups in the formed MOFs are vital for the fabrication of ultra‐small Pd nanoclusters as these groups can largely impede the migration of Pd nanoclusters at high temperatures owing to the strong interaction between the lone‐pair electrons of the N species and the 5d empty orbitals of the Pd ions . In contrast, without the assistance of the ‐NH 2 groups, the Pd species were inclined to aggregate into relatively large nanoparticles upon pyrolysis of the counterpart Pd@UiO‐66(Zr).…”

The Road to MOF-Related Functional Materials and Beyond: Desire, Design, Decoration, and Development

“…Moreover, a temperature‐controlled program has been successfully utilized in one‐step encapsulation of Pd NPs in MOFs (i.e., UiO‐67) 41. The synthesis route followed a cooperative in situ metal precursor incorporation (e.g., 80°C) and an on‐site moderate reduction process to fabricate MNPs at elevated temperatures (e.g., 130°C).…”

“…b) Catalytic hydrogenation of styrene to ethylbenzene. c) Yield of ethylbenzene versus time in the hydrogenation of styrene over Pd II ‐in‐UiO‐67, Pd‐in‐UiO‐67, and Pd@UiO‐67 41…”