Au@UiO-66: a base free oxidation catalyst

[EN] We present the in situ synthesis of Au nanoparticles within the Zr based Metal Organic Framework, UiO-66. The resulting Au@UiO-66 materials were characterized by means of N-2 sorption, XRPD, UV-Vis, XRF, XPS and TEM analysis. The Au nanoparticles (NP) are homogeneously distributed along the UiO-66 host matrix when using NaBH4 or H-2 as reducing agents. The Au@UiO-66 materials were evaluated as catalysts in the oxidation of benzyl alcohol and benzyl amine employing O-2 as oxidant. The Au@MOF materials exhibit a very high selectivity towards the ketone (up to 100%). Regenerability and stability tests demonstrate that the Au@UiO-66 catalyst can be recycled with a negligible loss of Au species and no loss of crystallinity. In situ IR measurements of UiO-66 and Au@UiO-66-NaBH4, before and after treatment with alcohol, showed an increase in IR bands that can be assigned to a combination of physisorbed and chemisorbed alcohol species. This was confirmed by velocity power spectra obtained from the molecular dynamics simulations. Active peroxo and oxo species on Au could be visualized with Raman analysis.K.L. acknowledges the nancial support from the Ghent University BOF postdoctoral grant 01P06813T and UGent GOA Grant 01G00710. M.V, S.T. and D.E. acknowledge funding from the Scientic Research-Foundation Flanders (FWO) for a postdoctoral fellowship. V.V.S. and M.W. acknowledge BELSPO in the frame of IAP-PAI P7/05. V.V.S. acknowledges funding from the European Research Council under the European Community's Seventh Framework Programme [FP7 (2007–2013) ERC grant agreement number 240483]. The computational resources and services used in this work were provided by VSC (Flemish Supercomputer Center), funded by the Hercules foundation and the Flemish Government – department EWI. This work was supported by funding from the European Research Council under the Seventh Framework Program (FP7), ERC grant no. 246791-COUNTATOMS.Leus, K.; Concepción Heydorn, P.; Vandichel, M.; Meledina, M.; Grirrane, A.; Esquivel, D.; Turner, S.... (2015). Au@UiO-66: a base free oxidation catalyst. RSC Advances. 5(29):22334-22342. https://doi.org/10.1039/C4RA16800CS223342234252

Origin of highly active metal-organic framework catalysts: defects? Defects!

SSCI-VIDE+ING+JEC:MVA:DFAInternational audienceThis article provides a comprehensive review of the nature of catalytic sites in MOFs. In the last decade, a number of striking studies havereported outstanding catalytic activities of MOFs. In all cases, theauthors were intrigued as it was unexpected from the ideal structure. Wedemonstrate here that (surface) defects are at the origin of thecatalytic activities for the reported examples. The vacancy of ligandsor linkers systematically generates (surface) terminations which canpossibly show Lewis and/or Bronsted acido-basic features. Theengineering of catalytic sites at the nodes by the creation of defects(on purpose) appears today as a rational approach for the design ofactive MOFs. Similarly to zeolite post-treatments, post-modifications ofMOFs by linker or metal cation exchange appear to be methods of choice.Despite the mild acidity of defective MOFs, we can account for veryactive MOFs in a number of catalytic applications which show higherperformances than zeolites or benchmark catalysts

Ab Initio Parametrized Force Field for the Flexible Metal–Organic Framework MIL-53(Al)

A force field is proposed for the flexible metal–organic framework MIL-53­(Al), which is calibrated using density functional theory calculations on nonperiodic clusters. The force field has three main contributions: an electrostatic term based on atomic charges derived with a modified Hirshfeld-I method, a van der Waals (vdW) term with parameters taken from the MM3 model, and a valence force field whose parameters were estimated with a new methodology that uses the gradients and Hessian matrix elements retrieved from nonperiodic cluster calculations. The new force field predicts geometries and cell parameters that compare well with the experimental values both for the large and narrow pore phases. The energy profile along the breathing mode of the empty material reveals the existence of two minima, which confirms the intrinsic bistable behavior of the MIL-53. Even without the stimulus of external guest molecules, the material may transform from the large pore (lp) to the narrow pore (np) phase [Liu et al. <i>J. Am. Chem. Soc.</i> <b>2008</b>, <i>120</i>, 11813]. The relative stability of the two phases critically depends on the vdW parameters, and the MM3 dispersion interaction has the tendency to overstabilize the np phase

A Robust Molecular Catalyst Generated In Situ for Photoand Electrochemical Water Oxidation

Water splitting is the key step towards artificial photosystems for solar energy conversion and storage in the form of chemical bonding. The oxidation of water is the bottle-neck of this process that hampers its practical utility; hence, efficient, robust, and easy to make catalytic systems based on cheap and earth-abundant materials are of exceptional importance. Herein, an in situ generated cobalt catalyst, [Co-II(TCA)(2)(H2O)(2)] (TCA=1-mesityl-1,2,3-1H-triazole-4-carboxylate), that efficiently conducts photochemical water oxidation under near-neutral conditions is presented. The catalyst showed high stability under photolytic conditions for more than 3 h of photoirradiation. During electrochemical water oxidation, the catalytic system assembled a catalyst film, which proved not to be cobalt oxide/hydroxide as normally expected, but instead, and for the first time, generated a molecular cobalt complex that incorporated the organic ligand bound to cobalt ions. The catalyst film exhibited a low overpotential for electrocatalytic water oxidation (360 mV) and high oxygen evolution peak current densities of 9 and 2.7 mA cm(-2) on glassy carbon and indium-doped tin oxide electrodes, respectively, at only 1.49 and 1.39 V ( versus a normal hydrogen electrode), respectively, under neutral conditions. This finding, exemplified on the in situ generated cobalt complex, might be applicable to other molecular systems and suggests that the formation of a catalytic film in electrochemical water oxidation experiments is not always an indication of catalyst decomposition and the formation of nanoparticles

Hydrogen evolution in alkaline medium on intratube and surface decorated PtRu catalyst

| openaire: EC/H2020/721065/EU//CREATEFor anion exchange membrane (AEM) electrolysis, challenges include finding an optimal catalyst for hydrogen evolution reaction (HER), as the noble metals are scarce while non-noble metals are inferior. Here, the noble metal amount is reduced in a straightforward solution synthesis which produces Pt-Ru surface nanoparticles and unique intratube nanowires decorated on single walled carbon nanotubes (SWNT). In half-cell tests, 5 wtPtRu-% Pt-Ru SWNT demonstrates stable 10 mA cm−2 HER current at 46 mV overpotential and outperforms commercial electrocatalysts. When integrated in an AEM electrolyser, a high current density of 500 mA cm−2 at a low voltage of 1.72 V is achieved with 34 µg cm−2 metal loading. First-principles calculations reveal that both the Pt-Ru alloy nanoparticle and intratube nanowires promote near optimal H* binding energy, thereby releasing the H2 faster. Thus, our approach yields an active low metal loading alkaline HER catalyst without sacrificing the performance in an AEM electrolyser.Peer reviewe

Base catalytic activity of alkaline earth MOFs: a (micro)spectroscopic study of active site formation by the controlled transformation of structural anions

A new method has been developed for generating highly dispersed base sites on metal–organic framework (MOF) lattices. The base catalytic activity of two alkaline earth MOFs, M2(BTC)(NO3)(DMF) (M ¼ Ba or Sr, H3BTC ¼ 1,3,5-benzenetricarboxylic acid, DMF ¼ N,N-dimethylformamide) was studied as a function of their activation procedures. The catalytic activity in Knoevenagel condensation and Michael addition reactions was found to increase strongly with activation temperature. Physicochemical characterization using FTIR, 13C CP MAS NMR, PXRD, XPS, TGA-MS, SEM, EPR, N2 physisorption and nitrate content analysis shows that during activation, up to 85% of the nitrate anions are selectively removed from the structure and replaced with other charge compensating anions such as O2_. The defect sites generated via this activation act as new strong basic sites within the catalyst structure. A fluorescence microscopic visualization of the activity convincingly proves that it is exclusively associated with the hexagonal crystals, and that reaction proceeds inside the crystal's interior. Theoretical analysis of the Ba-material shows that the basicity of the proposed Ba2+–O2_–Ba2+ motifs is close to that of the edge sites in BaO.crosscheck: This document is CrossCheck deposited related_data: Supplementary Information copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: The accepted version of this article will be made freely available after a 12 month embargo period history: Received 11 June 2014; Accepted 25 July 2014; Accepted Manuscript published 25 July 2014; Advance Article published 13 August 2014; Version of Record published 29 September 2014status: publishe

Synthesis modulation as a tool to increase the catalytic activity of metal-organic frameworks: the unique case of UiO-66(Zr)

The catalytic activity of the zirconium terephthalate UiO-66(Zr) can be drastically increased by using a modulation approach. The combined use of trifluoroacetic acid and HCl during the synthesis results in a highly crystalline material, with partial substitution of terephthalates by trifluoroacetate. Thermal activation of the material leads not only to dehydroxylation of the hexanuclear Zr cluster but also to post-synthetic removal of the trifluoroacetate groups, resulting in a more open framework with a large number of open sites. Consequently, the material is a highly active catalyst for several Lewis acid catalyzed reactions