Manuel Sánchez-Sánchez

Cobalt Doping of the MOF-5 Framework and Its Effect on Gas-Adsorption Properties

Partial isomorphic substitution of Zn in IRMOF metal clusters by cobalt ions is described for the first time. Specifically, different numbers of Co(2+) ions have been incorporated during solvothermal crystallization into the Zn-based MOF-5 (IRMOF-1) framework, which is one of the most studied MOF materials. The amount of Zn that can be substituted seems to be limited, being no more than 25% of total metal content, that is, no more than one Co atom inside every metal cluster formed by four transition-metal ions, on average. Several characterization techniques, including X-ray diffraction, DR UV-visible spectroscopy, N(2) adsorption isotherms, and thermogravimetrical analysis, strongly support the effective incorporation of Co into the material framework. As-synthesized CoMOF-5 has cobalt ions in octahedral coordination, changing to tetrahedral by simple evacuation, presumably by the removal of two diethylformamide molecules per Co ion. Moreover, the H(2), CH(4), and CO(2) uptake of MOF-5 materials systematically increases with the Co content, particularly at high pressure. Such an increase is moderate anyway, considering that Co is incorporated into unexposed metal sites that are less accessible to gas molecules.

Synthesis of metal–organic frameworks in water at room temperature: salts as linker sources

Exponential growth in the interest in MOF (Metal–Organic Framework) materials in both scientific and industrial spheres has been flourishing in the last fifteen years. However, certain environmental and economic limitations could slow down their industrial establishment. Here we present an innovative, widely applicable, straightforward, rapid, inexpensive and environmentally friendly method to prepare high-quality carboxylate-based MOFs with properties rarely obtained under conventional conditions. The method is based on the use of organic salts (instead of their homologous protonated organic ligands) as anionic linker sources, so that their solubility and the deprotonation steps, which necessarily take place in the formation of MOFs, are notably favoured in aqueous solution. As an example, the preparation of X-MIL-53-Al (X = none, NH2, NO2) materials is reported at room temperature, with the following additional advantages for some applications: they (i) are nanocrystalline, (ii) have notable and ordered inter-crystalline mesoporosity, and (iii) contain a reduced or even a negligible amount of unreacted linker within the pores. To the best of our knowledge, this is the first preparation of a 3-D highly-porous MOF under these two industrially-demanded synthesis conditions: room temperature and water as the sole solvent. The scarce commercial availability of these linker salts is a limitation that can be easily circumvented by replacing the salts with their protonated analogue plus a base. Following this method, a high-quality MOF-74 material, so far only prepared in organic solvents, could be also prepared in water and at room temperature. Even in organic media, in which this approach could be a priori unfavourable from a linker solubility point of view, MOFs with properties unattainable through conventional methods of synthesis can be prepared following this approach. That is the case for the synthesis of MOF-5 with the highest interpenetration degree ever described by just replacing terephthalic acid with disodium terephthalate as the linker source and maintaining the otherwise conventional conditions including the use of DMF as the solvent.

Nanocrystalline M–MOF-74 as Heterogeneous Catalysts in the Oxidation of Cyclohexene: Correlation of the Activity and Redox Potential

In some aspects, the potential of metal–organic framework (MOF) materials as heterogeneous catalysts has been realized, at least in an academic context. However, one of their most promising catalytic properties, that is, the presence of open metal sites, is far from understood properly. In this work, a series of M–MOF‐74 (M=Mn, Co, Ni, Cu, Zn) materials, prepared under sustainable conditions, was tested systematically in the oxidation of cyclohexene, which can proceed by either radical or epoxidation routes. Under the optimized reaction conditions, the radical route is spontaneous to some extent and it is enhanced in the presence of any M–MOF‐74 that has a metal with a redox character but not Zn. However, the epoxidation of cyclohexene is also promoted by a redox catalyst in such a way that the conversion correlates qualitatively with the redox potential of the metal. Thus, for the first time, a chemical property of M is correlated with the catalytic activity of the M–MOF‐74 family.

Catalytic activity of HKUST-1 in the oxidation of trans-ferulic acid to vanillin

HKUST-1 was used as a catalyst in the conversion of trans-ferulic acid to vanillin. The generation of unsaturated metal sites within HKUST-1 is the fundamental step in the catalytic process. When activated under vacuum, the catalyst gives complete conversion in only 1 h with a significant average reaction yield of 95%.

Room temperature synthesis of metal organic framework MOF-2

One of the pioneering metal organic framework material, called MOF-2 and having the formula [Zn2(BDC)2], still continues awakening interest amongst the scientific community in spite of its layered character. However, the synthesis methods are either experimentally complicated or in two steps through the transformation of MOF-1. Here, we describe the preparation of a high-quality MOF-2 under more sustainable conditions, including room temperature, absence of any amine or any other pH-controller, partial substitution of the harmful organic solvent (N,N-dimethylformamide) by water, and by simply mixing linker and metal sources, the latter being zinc acetate, carefully selected as a function of their solubility in the solvent mixture. The optimum ratio of Zn(OAc)2·4H2O to terephthalic acid (H2BDC) is 1.74 and H2O to DMF is 3. MOF-2 [Zn2(BDC)2] has been characterized using powder X-ray diffraction, thermogravimetric analysis, N2 adsorption/desorption and scanning electron microscopy, all of them supporting the good quality of the material.

On the Sn(II) and Sn(IV) incorporation into the AFI-structured AlPO4-based framework: the first significantly acidic SnAPO-5

Both Sn(II) and Sn(IV) chlorides were tested as sources for tin incorporation into an AlPO4-5 framework. N-Methyldicyclohexylamine (MCHA) was chosen as a structure-directing agent, taking advantage of its reported high specificity towards AFI-structured AlPO4-based materials. Pure AFI materials were successfully produced, irrespective of the Sn source in a wide range of gel compositions. Whereas the different characterization techniques of the Sn(IV)APO-5 materials certify the unfavourable (or at least low-quality) incorporation of Sn, as expected from previous studies, there is no doubt about the right Sn(II) incorporation into the AlPO4 framework. The amount of Sn(II) able to be properly incorporated into the AlPO4-5 structure is significantly higher than that described in the literature for Sn(IV)APO-5 materials as well as for the Sn(IV)APO-5 materials prepared in this work. For the first time, AlPO4-based microporous catalysts were tested in the Friedel–Crafts acylation of anisole. Supporting the characterization results, Sn(IV)APO-5 and especially Sn(II)APO-5 were active catalysts in such reactions which require acid centers to take place. Since all tested AlPO4-based materials (pure AlPO4-5, SAPO-5 and SnAPO-5) possess an AFI structure and similar surfaces areas, the extent of the acylation of anisole was taken as indirect proof of acidic strength. The conversion given by pure AlPO4-5 was negligible in comparison with Sn(II)APO-5, which overcomes the activity of the SAPO-5 and even that of a standard zeolite H-beta.

Atomic Observations of Microporous Materials Highly Unstable under the Electron Beam: The Cases of Ti‐Doped AlPO4‐5 and Zn–MOF‐74

This work presents the highest resolution micrographs reported so far of two beam‐sensitive microporous materials: Ti‐doped AlPO4‐5 (TAPO‐5) and the metal–organic framework Zn–MOF‐74. They were registered by means of Cs‐corrected STEM. The high‐resolution images of the TAPO‐5 along the [0 0 1] orientation allows a clear observation of the aluminophosphate‐five (AFI) type framework, and illustrates the atomic distribution of the “T” atoms of the structure. However, no definitive conclusions about Ti substitution mechanism could be afforded because of the high symmetry of the AFI framework. In the case of Zn–MOF‐74, the images were also obtained at 300 kV proving that under certain conditions of beam current this technique can provide invaluable information of an ever‐increasing variety of molecular sieves.

Towards an Environmentally Acceptable Heterogeneous Catalytic Method of Producing Adipic Acid by the Oxidation of Hydrocarbons in Air

A survey is given of the catalytic methods potentially available for the production of adipic acid by the oxidation of readily available hydrocarbon precursors under environmentally benign conditions. Encouraging results are reported using H2O2 as oxidant and microporous FeAlPO-5 as catalyst at moderate temperatures.

Glycerol conversion into H2 by steam reforming over Ni and PtNi catalysts supported on MgO modified γ-Al2O3

Abstract The glycerol catalytic steam reforming over Ni and PtNi catalysts to produce H 2 was studied. The activity results indicate that the catalyst with the lower content of MgO, the NiA1M, provides higher H 2 molar ratios than the Ni catalyst. The behaviour of the NiA1M catalysts seems to be related to the Ni o species stabilization by nickel-magnesia interactions, which are favoured by the presence of well dispersed MgAl 2 O 4 spinels. The bimetallic catalyst, PtNiA3M named, reforms the intermediate products improving the activity of the Ni monometallic catalyst toward H 2 production. The characterization results suggest that the Pt in the Ni monometallic catalyst enhances the Ni o particles dispersion and the nickel species reducibility by H 2 spillover.

Nearly room-temperature crystallisation of Zn-doped AlPO4-based chabazite materials

A series of ZnAPO-34 materials has been synthesised from gels containing TEAOH as structure-directing agent under a very wide range of crystallisation temperatures. Varying both gel composition and crystallization times, ZnAPO-34 samples can be obtained at temperatures as low as 40 °C, and also at temperatures as high as 200 °C. It probably converts this system in the most specific system towards a particular microporous structure, at least in terms of crystallisation temperatures. The crystal size of the chabazite-structured materials has been studied as a function of crystallization temperature. As expected, the materials synthesized at lower temperatures are formed by larger crystals.