Zirconia-supported 11-molybdovanadophosphoric acid catalysts: effect of the preparation method on their catalytic activity and selectivity.

The oxidation of adamantane with hydrogen peroxide catalyzed by zirconia-supported 11-molybdovanadophosphoric acid is shown to be a suitable green route for the synthesis of adamantanol and adamantanone. This work evaluates how the catalyst activity and selectivity are affected by some of its preparative parameters, such as the method for supporting the catalytically active heteropoly acid over the zirconia matrix or the pretreatments applied to the resulting materials before being used as heterogeneous catalysts. Our results indicate that the most effective catalysts able to maintain their activity after several reaction runs are those prepared by following the sol-gel route, whereas the most selective catalysts are those obtained by impregnation methods. Moreover, the calcination temperature has also been identified as a relevant parameter influencing the performance of catalysts based on supported heteropoly acids. The increasing catalytic activity observed over several consecutive reaction runs has been attributed to the formation of peroxo derivatives of polyoxometalate clusters at the surface of the catalyst and their accumulation after each reaction cycle.

A Simple Approach To Develop Tailored Mesoporosity in Nanostructured Heteropolysalts.

In this study, we describe a very simple approach to the development of tailored mesoporosity in any nanostructured heteropolysalt with control over both the mesoporous volume and the pore size. This approach, which consists in the treatment of a solid microporous precursor with a basic agent, has been tested on the ammonium salt of the Keggin-type [PMo12 O40 ]3- heteropolyanion and constitutes a novel procedure for the preparation of mesoporous solids with no precedents. The results obtained in this study allow two main conclusions to be drawn: 1) the micro- and mesoporous structures in the heteropolysalt nanoparticles are independent from each other and 2) the development of mesoporosity in the solid material must be related to a process of alkaline degradation within the core of the nanocrystals that aggregate into the particles. These results afford valuable additional information to the present model of porosity that has been established for heteropolysalts.

A Robust Open Framework Formed by Decavanadate Clusters and Copper(II) Complexes of Macrocyclic Polyamines: Permanent Microporosity and Catalytic Oxidation of Cycloalkanes.

The first decavanadate-based microporous hybrid, namely, [Cu(cyclam)][{Cu(cyclam)}2(V10O28)]·10H2O (1, cyclam = 1,4,8,11-tetraazacyclotetradecane) was prepared by reaction of (VO3)(-) anions and {Cu(cyclam)}(2+) complexes in NaCl (aq) at pH 4.6-4.7 and characterized by elemental analyses, thermogravimetry, and X-ray diffraction (powder, single-crystal) techniques. Compound 1 exhibits a POMOF-like supramolecular open-framework built of covalent decavanadate/metalorganic layers with square-like voids, the stacking of which is aided by interlamellar cementing complexes and generates water-filled channels with approximate cross sections of 10.4 × 8.8 Å(2). The framework is robust enough to remain virtually unaltered upon thermal evacuation of all water molecules of hydration, as demonstrated through single-crystal X-ray diffraction studies on the anhydrous phase 1a. This permanent microporosity renders interesting functionality to 1, such as selective adsorption of CO2 over N2 and remarkable activity as heterogeneous catalyst toward the H2O2-based oxidation of the highly-stable, tricyclic alkane adamantane.