The nature of the active Ti species in TiCl 3 -doped NaAlH 4 , a promising hydrogen storage material, was studied as a function of the desorption temperature with Ti K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, Ti K-edge X-ray absorption near-edge structure (XANES) spectroscopy, and X-ray diffraction (XRD). In the freshly prepared sample, Ti was amorphous and surrounded by 4.8 Al atoms divided between two shells at 2.71 and 2.89 Å. In the next shell, 1.9 Ti atoms were detected at 3.52 Å. It was concluded that 30% of Ti was incorporated into the surface of Al crystallites and 70% of Ti occupied interstitials in the NaAlH 4 lattice, possibly forming trimeric, triangular Ti entities. After hydrogen desorption at 125°C, NaAlH 4 decomposed and the Ti-Al coordination number increased from 4.8 to 8.5. We propose that all Ti is incorporated into the surface layer of the formed Al. After the material was heated to 225°C, the local structure of Ti, as inferred from EXAFS and XANES spectroscopy, was identical to the local structure of a TiAl 3 alloy. However, the formed alloy was amorphous and was only detected in XRD by an increase of the background intensity around the Al diffraction. These so-called "TiAl 3 clusters" agglomerated in the heat treatment to 475°C, forming crystalline TiAl 3 . Earlier work has shown that increasing the desorption temperature of NaAlH 4 lowers the absorption rate and capacity of hydrogen in the next step. Thus, by comparing our results with absorption properties published in the literature on similar samples, we could rank the activity of the Ti for hydrogen absorption as Ti in the Al surface > TiAl 3 cluster > crystalline TiAl 3 , therewith indicating that Ti incorporated into the surface of Al is the most active for the absorption of hydrogen.

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The use of the metal organic framework MIL-101(Cr) as support for Pt nanoparticles is evaluated in three selective hydrogenation reactions. Homogenous Pt nanoparticles of ∼4 nm can be formed inside the porosity of MIL-101(Cr) in close contact with the Cr trimers in an eggshell configuration by a wet impregnation procedure combined with sonication. The catalyst is applied in the selective hydrogenations of olefin mixtures, benzonitrile, and linoleic acid. In the case of an olefin mixture, 1-octene is selectively hydrogenated over 1-hexadecene, attributed to diffusion limitations that favor the hydrogenation of the smaller substrate. In the case of benzonitrile hydrogenation, benzylamine is selectively formed over dibenzylamine attributed to transition state selectivity. In the hydrogenation of linoleic acid, selectivities were similar to that for platinum on alumina.

Thermal treatment of phosphotungstic acid (PTA)-MIL-101(Cr) composites in the presence of hydroformylation catalyst RhH(CO)(PPh 3 ) 3 leads to immobilization of the homogeneous Rh complex within the metal-organic framework (MOF) scaffold by coordination of PTA-Rh. The Rh complex-containing MOFs are tested in the hydroformylation of 1-octene in which PTAc ompetes with CO during ligand association.I nt he presence of the carbonyll igand,t he Rh complex is released from the MOF and behaves as ah omogeneous catalyst. Therefore, the product spectra and selectivities of the Rh complex-containing MOFs are similart ot hose of RhH(CO)(PPh 3 ) 3 .U pon CO evacuation, Rh recoordinates to PTA, allowingf or easy recycling of this new pseudo-heterogeneous catalyst.The hydroformylation reactioni sl argely applied in industry to the production of aldehydes ando ther bulk chemical platforms.[1] Although the state-of-the-artr eactioni sh omogeneously catalyzed, many attempts have been made to immobilize organometallic complexesf or heterogeneous processes. To this end, various organic and inorganic materials (e.g.,S iO 2 , Al 2 O 3 ,p olymers,a ctivated carbon, and zeolites) have been studied and functionalizedi nm anyw ays.[2] Although promising examples are reportedw ith respectt oc atalystp erformance and recyclability,m etal leaching is ac ommon challenge to overcome in these systems. Moreover, dynamics of the complex in terms of ligand dissociation-association and flexibility may be affectedupon immobilization. [3] Metal-organic frameworks (MOFs) hold unbeatable internal volumes and adsorption capacities. Moreover,t hey can be utilized as catalysts by variousa pproaches, one being the use of their empty space,o ften referred to as encapsulation.[4] Already,afew examples have been reported in the literature on the utilization of MOFs as hydroformylation catalysts.[5] Encapsulationi sm ore feasible in cage-type structures such as the MIL-101 family.[6] MIL-101(Cr) is as table MOF that consists of approximately3 0 diameter cavities with openings of 12 and 16 .[7] Polyoxometalate MOF composites based on MIL-101 have already been synthesized and used in catalysis. [6, 8] Polyoxometalates are known to act as mild coordinating ligands in homogeneous catalysis, with ac oordination strength lower than that of CO.[9] Therefore, use of ap hosphotungstic acid (PTA)-MOF composite is considered for the dynamic coordination of the RhH(CO)(PPh 3 ) 3 hydroformylation catalyst. Indeed, the objective of this study,r ather than immobilization in its conventional sense, is to utilizeM OFs as scaffolds for handling and recycling the Rh-based hydroformylation catalyst and to control its releasei nt he reaction environmentb yC O coordination:inthe absence of CO the catalysts would stay coordinated to the PTA-MOF solid but, at high CO pressure, the homogenous complex would detach from the MOF.R emoval of CO from the environment should result in recoordination of the catalystt othe PTA-MOFcomposite and enable recycling.MIL-101(Cr) wasp repared by h...