Structural reversibility of Cu doped NU-1000 MOFs under hydrogenation conditions

0522597 - ÚFCH JH 2021 RIV US eng J - Journal Article
Halder, A. - Lee, S. - Yang, B. - Pellin, M. J. - Vajda, Štefan - Li, Z. - Yang, Y. - Farha, O. K. - Hupp, J. T.
Structural reversibility of Cu doped NU-1000 MOFs under hydrogenation conditions.
Journal of Chemical Physics. Roč. 152, č. 8 (2020), č. článku 084703. ISSN 0021-9606. E-ISSN 1089-7690
EU Projects: European Commission(XE) 810310
Institutional support: RVO:61388955
Keywords : metal–organic framework * nanoparticles * clusters
OECD category: Physical chemistry
Impact factor: 3.488, year: 2020
Method of publishing: Open access

The metal–organic framework (MOF), NU-1000, and its metalated counterparts have found proof-of-concept application in heterogeneous catalysis and hydrogen storage among others. A vapor-phase technique, akin to atomic layer deposition (ALD), is used to selectively deposit divalent Cu ions on oxo, hydroxo-bridged hexa-zirconium(IV) nodes capped with terminal –OH and –OH2 ligands. The subsequent reaction with steam yields node-anchored, CuII-oxo, hydroxo clusters. We find that cluster installation via AIM (ALD in MOFs) is accompanied by an expansion of the MOF mesopore (channel) diameter. We investigated the behavior of the cluster-modified material, termed Cu-AIM-NU-1000, to heat treatment up to 325 °C at atmospheric pressure with a low flow of H2 into the reaction cell. The response under these conditions revealed two important results: (1) Above 200 °C, the initially installed few-metal-ion clusters reduce to neutral Cu atoms. The neutral atoms migrate from the nodes and aggregate into Cu nanoparticles. While the size of particles formed in the MOF interior is constrained by the width of mesopores (∼3 nm), the size of those formed on the exterior surface of the MOF can grow as large as ∼8 nm. (2) Reduction and release of Cu atoms from the MOFs nodes is accompanied by the dynamic structural transformation of NU-1000 as it reverts back to its original dimension following the release. These results show that while the MOF framework itself remains intact at 325 °C in an H2 atmosphere, the small, AIM-installed CuII-oxo, hydroxo clusters are stable with respect to reduction and conversion to metallic nanoparticles only up to ∼200 °C.
Permanent Link: http://hdl.handle.net/11104/0307065