The loading of [Zn4O(bdc)3] (MOF-5; bdc = 1,4-benzenedicarbocylate) with nanocrystalline Cu and ZnO species was achieved in a two-step process. First, the solvent-free gas-phase adsorption of the volatile precursors [CpCuL] (L = PMe3, CNtBu) and ZnEt2 leads to the isolable inclusion compounds precursor@MOF-5. These intermediates were then converted into Cu@MOF-5 and ZnO@MOF-5 by hydrogenolysis or photoassisted thermolysis at 200−220 °C in the case of Cu and hydrolysis or dry oxidation at 25 °C followed by annealing 250 °C in the case of ZnO. 17O labeling studies using H2 17O (30%) revealed that neither the bdc linkers nor the central oxide ion of the Zn4O unit exchange oxygen atoms/ions with the imbedded ZnO species. The obtained material Cu@MOF-5 (11 wt % Cu), exhibiting an equivalent Langmuir surface of 1100 m2·g−1, was further characterized by powder X-ray diffraction (PXRD), X-ray absorption spectroscopy (XAS), and transmission electron microscopy (TEM). The Cu nanoparticles are homogeneously distributed over the MOF-5 microcrystals, occupying only about 1% of the cavities. Their size distribution appears to be polydisperse with a majority around 1 nm in size (by EXAFS) together with a minority of larger particles up to 3 nm (PXRD). Cu@MOF-5 was reversibly surface oxidized/reduced by N2O/H2 treatment, resulting in a (Cu2O/Cu)@MOF-5 material as revealed by PXRD and XAS. Depending on the preparation conditions of the ZnO@MOF-5 materials a variation of the ZnO loading from 10 to 35 wt % was achieved. PXRD, TEM, UV−vis, and 17O-MAS NMR spectroscopy gave evidence for a largely intact MOF-5 matrix with imbedded ZnO nanoparticles <4 nm being in the quantum size regime. Doubly-loaded (Cu/ZnO)@MOF-5 samples were prepared by gas-phase loading of ZnO@MOF-5 with [CpCuL] followed by thermally activated hydrogenolysis. The initial catalytic productivity in methanol synthesis from a CO/CO2/H2 gas mixture at 1 atm and 220 °C peaked at about 60% of an industrial reference catalyst. This result is particular surprising because of the comparably low Cu loading (1.4 wt %) and small Cu specific surface area <1 m2·g−1, thus suggesting a superior interfacial contact between the Cu and ZnO nanophases. However, the materials (Cu/ZnO)@MOF-5 were unstable under catalytic conditions over several hoours, the metal organic framework collapsed, and the final catalytic activities were poor.

Metal-organic frameworks have recently attracted attention as heterogeneous catalysts due to their high content of metal centres and large surface area and pore volume, along with their impressive topological richness. Therefore, many studies describing the use of MOFs as heterogeneous Lewis acid catalysts have been published. In this regard, these efforts have been directed towards probing the catalytic activity. Further information is required in terms of kinetic parameters and comparison of performance with their homogeneous counterparts, or other conventional heterogeneous catalysts. Here we have attempted to put MOFs into perspective with respect to their homogeneous counterparts and more conventional heterogeneous catalysts to show their advantages and limitations. We have exemplified a number of reactions reported in the literature wherein MOFs have been used as catalysts, and we have carried them out using homogeneous counterparts, i.e. benzoates and acetates, and other well defined conventional solid catalysts. The activities and selectivities of the catalysts are compared and then put into perspective on the basis of kinetic parameters, such as turnover numbers and turnover frequencies.Additionally, we illustrate using selected examples what the potential advantages of MOF catalysts could be, and how they may outperform the potential of other solid catalysts.

Nanoscale titania particles were synthesized inside the porous coordination polymer [Zn(4)O(bdc)(3)] (bdc = 1,4-benzene-dicarboxylate, MOF-5) by adsorption of titanium isopropoxide from the gas-phase and subsequent dry oxidation and annealing.

The highly porous and desolvated (activated) coordination polymer [Zn 4 O(btb) 2 ] (btb ¼ benzene -1,3,5tribenzoate; MOF-177) was loaded with the organometallic compounds [Cp 2 Fe], [Cp* 2 Zn], [Cu(OCHMeCH 2 NMe 2 ) 2 ], [CpCuL] (L ¼ PMe 3 , CNtBu) and [CpPd(h 3 -C 3 H 5 )] via solvent-free adsorption from the gas-phase. The inclusion compounds of the type [L n M]

Low-temperature CO oxidation is among the most interesting reactions in heterogeneous catalysis. It is well known that this reaction can be catalyzed by gold deposited as nanoparticles on metal oxide surfaces (e.g. TiO 2 , MgO, and ZnO). [1] Developing highly efficient and low-cost catalysts for low-temperature CO oxidation represents a major challenge. Most recently, Cubased metal-organic frameworks (MOFs) have been identified for efficient CO oxidation at ambient pressure and elevated temperatures, namely [Cu 3 btc 2 ] (btc= benzene-1,3,5-tricarboxylate ) and [Cu 5 (OH) 2 (nip) 4 (H 2 O) 6 ] (H 2 O) 4.25 (nip = 5-nitroisophthalate) with 100 % conversion at 240 8C and 200 8C, respectively. [2,3] However, the origin of the catalytic activity of such Cu-MOFs is not well understood.Coordinatively unsaturated metal ion sites (CUS) at the backbone of MOFs [4] are known to play an important role for catalysis, [5] gas storage, [6] chemical sensing, [7] and other applications. For catalysis, Schlichte et al. [8] reported on the cyanosilylation of benzaldehyde and acetone with [Cu 3 btc 2 ] as catalyst (HKUST-1, [9] Figure S1) for which its activity was assigned to the Lewis acid properties of intrinsic Cu 2 + CUS at the copper-carboxylate paddle-wheel building unit (CuPW) of this prototypical MOF in its dehydrated form. The characterization of reactive CUS of MOFs with infrared spectroscopic techniques and suitable probe molecules, quite similar to classic heterogeneous catalysts, [10] is expected to provide most valuable information for mechanistic understanding and fine tuning of the MOF materials.Herein, we present our studies on the in situ monitoring of the co-adsorption of CO and O 2 at [Cu 3 btc 2 ] (HKUST-1) [9] and its congener [Cu 3 btb 2 ] (MOF-14, [11] btb = benzene-1,3,5-tribenzoate) by using an ultrahigh vacuum infrared spectroscopy tool (UHV-FTIRS). [12] The high-quality IR data provide unambiguous spectroscopic evidence for the surprisingly high catalytic activity of both Cu-MOFs samples for CO oxidation at temperatures as low as 105 K, according to Scheme 1.

The Zn-carboxylate-based porous coordination polymer @MOF-5. These composites were decomposed to Au@MOF-5, Au/ZnO@MOF-5 and Au/TiO 2 @MOF-5 under hydrogen at 100°C. The nanoparticle-loaded hybrid materials were characterised by powder X-ray diffraction (PXRD), IR spectroscopy, X-ray photoelectron spectroscopy (XPS) and N 2 sorption measurements, which reveal an intact MOF-5 structure that maintains a high specific surface area. For Au@MOF-5, crystalline Au nanoparticles were distributed over the MOF matrix in a homogeneous fashion with a size of ca. 1-3 nm, evidenced by high resolution transmission

The unique host-guest chemistry of metal-organic frameworks (MOFs) can be used to implement additional properties by loading the cavities with functional molecules or even nanoparticles. We describe the gas-phase loading of MOFs featuring either a three-dimensional (MOF-5, MOF-177 and UMCM-1) or one-dimensional channel system (MIL-53(Al)) with the highly emissive perylene derivative N,N-bis(2,6-dimethylphenyl)-3,4:9,10-perylene tetracarboxylic diimide (DXP) or an iridium complex, (2-carboxypyridyl)bis(3,5-difluoro-2-(2-pyridyl)phenyl)iridium(III) (FIrpic). The resulting host-guest composites show strong luminescence, with their optical properties being dominated by the guest species. DXP-loaded MOFs exhibit a high stability towards guest displacement by solvent molecules, while the interaction of FIrpic with the host is weaker. The emissive properties of intercalated DXP also indicate host-guest interactions such as caging effects, strong quenching of the MOF host emission, as well as aggregate formation.

Low‐temperature CO Oxidation The cover picture shows the adsorption and oxidation of CO at Cu‐based metal‐organic frameworks (HKUST‐1 and MOF‐14). In their Communication on R. A. Fischer, Y. Wang et al. investigate the reaction mechanism of low‐temperature CO oxidation by using ultra‐high vacuum infrared spectroscopy (UHV‐FTIRS) combined with density functional theory (DFT) calculations. In their communication they provide direct spectroscopic evidence for the high catalytic activity of Cu‐based MOFs toward CO oxidation at 105 K. The high‐quality FTIRS data demonstrate that this reaction takes place on both intrinsic Cu2+ CUS (coordinatively unsaturated sites) and minority Cu2+ defect sites in the framework. A concerted mechanism was proposed, where the impinging O2 molecule is activated in the presence of pre‐adsorbed CO and interacts simultaneously with two isocarbonyl species at neighboring CUS to yield two CO2 molecules.