Reactivity in the confined spaces of zeolites: the interplay between spectroscopy and theory to develop structure-activity relationships for catalysis.

The Lewis acid properties of a series of isolated and well-defined Sn centers in different micro- and mesoporous materials have been investigated by means of DFT calculations and IR spectroscopy of probe molecules, and the results have been related to the experimentally measured catalytic activity of these materials for different reactions. Different types of Sn centers have been detected and modelled: inactive fully coordinated Sn atoms in framework positions that weakly interact with Lewis bases, and highly active strong Lewis acid sites associated with Sn centers with one or two hydrolyzed Sn-O-Si bridges. The relative amount of strong and weak sites depends on the zeolite structure, and can be modified by the catalyst pre-treatment conditions. On the other hand, it has been established that Sn-containing mesoporous materials obtained either by direct synthesis or by post-synthesis incorporation of Sn, show a similar distribution of centers. Finally, the influence of solvent and free space available around the active site on the diastereoselectivity of the cyclization of citronellal to isopulegol were investigated, and some hints were obtained on how to improve the catalyst performance.

[1]  V. Ramaswamy,et al.  Synthesis and characterization of crystalline, tin-silicate molecular sieves with MFI structure , 1994 .

[2]  W. R. Wadt,et al.  Ab initio effective core potentials for molecular calculations. Potentials for main group elements Na to Bi , 1985 .

[3]  G. Chuah,et al.  Liquid-phase Oppenauer oxidation of primary allylic and benzylic alcohols to corresponding aldehydes by solid zirconia catalysts , 2004 .

[4]  A. Corma,et al.  Observation of a 390-nm Emission Band Associated with Framework Ti in Mesoporous Titanosilicates , 2000 .

[5]  A. V. Ramaswamy,et al.  Hydroxylation of phenol over Sn-silicalite-1 molecular sieve: solvent effects , 1996 .

[6]  A. Corma,et al.  Selective and shape-selective Baeyer-Villiger oxidations of aromatic aldehydes and cyclic ketones with Sn-beta zeolites and H2O2. , 2002, Chemistry.

[7]  A. Corma,et al.  A general method for the preparation of ethers using water-resistant solid lewis acids. , 2007, Angewandte Chemie.

[8]  A. Corma,et al.  Lewis acids: from conventional homogeneous to green homogeneous and heterogeneous catalysis. , 2003, Chemical reviews.

[9]  A. Corma,et al.  Sn-MCM-41--a heterogeneous selective catalyst for the Baeyer-Villiger oxidation with hydrogen peroxide. , 2001, Chemical communications.

[10]  A. Corma,et al.  Sn-zeolite beta as a heterogeneous chemoselective catalyst for Baeyer–Villiger oxidations , 2001, Nature.

[11]  S. Akutagawa.  Enantioselective isomerization of allylamine to enamine: practical asymmetric synthesis of (–)-menthol by Rh–BINAP catalysts , 1997 .

[12]  Avelino Corma,et al.  Attempts to Fill the Gap Between Enzymatic, Homogeneous, and Heterogeneous Catalysis , 2004 .

[13]  A. Corma,et al.  A New Environmentally Benign Catalytic Process for the Asymmetric Synthesis of Lactones: Synthesis of the Flavouring δ-Decalactone Molecule , 2004 .

[14]  A. Corma,et al.  Mechanism of the Meerwein-Ponndorf-Verley-Oppenauer (MPVO) redox equilibrium on Sn- and Zr-beta zeolite catalysts. , 2006, The journal of physical chemistry. B.

[15]  W. M. Meier,et al.  Crystal structure and structure-related properties of ZSM-5 , 1981 .

[16]  G. Bellussi,et al.  Production of titanium containing molecular sieves and their application in catalysis , 2001 .

[17]  A. Corma,et al.  Lewis acidic Sn(IV) centers-grafted onto MCM-41-as catalytic sites for the Baeyer-Villiger oxidation with hydrogen peroxide , 2003 .

[18]  A. Corma,et al.  Uniform catalytic site in Sn-beta-zeolite determined using X-ray absorption fine structure. , 2005, Journal of the American Chemical Society.

[19]  Wang,et al.  Accurate and simple analytic representation of the electron-gas correlation energy. , 1992, Physical review. B, Condensed matter.

[20]  N. Erdman,et al.  Synthesis and characterization of Sn-Beta as a selective oxidation catalyst , 2004 .

[21]  A. Corma,et al.  Electrochemical characterization of two different framework Ti(IV) species in Ti/Beta zeolites in contact with solvents , 2000 .

[22]  W. M. Meier,et al.  Structure of synthetic zeolite ZSM-5 , 1978, Nature.

[23]  A. Becke.  Density-functional thermochemistry. III. The role of exact exchange , 1993 .

[24]  A. Corma,et al.  A new, alternative, halogen-free synthesis for the fragrance compound Melonal using zeolites and mesoporous materials as oxidation catalysts , 2005 .

[25]  H. Frei,et al.  Photochemical and FT-IR probing of the active site of hydrogen peroxide in Ti silicalite sieve. , 2002, Journal of the American Chemical Society.

[26]  J. Newsam,et al.  Structural characterization of zeolite beta , 1988, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[27]  A. Corma,et al.  One step synthesis of highly active and selective epoxidation catalysts formed by organic–inorganic Ti containing mesoporous composites , 1998 .

[28]  A. Corma,et al.  Determination of the catalytically active oxidation Lewis acid sites in Sn-beta zeolites, and their optimisation by the combination of theoretical and experimental studies , 2005 .

[29]  B. Weckhuysen,et al.  Spectroscopic Characterization of Supported Cr and Cr, Ti catalysts : interaction with probe molecules , 1995 .

[30]  A. Corma,et al.  Sn-Beta zeolite as diastereoselective water-resistant heterogeneous Lewis-acid catalyst for carbon-carbon bond formation in the intramolecular carbonyl-ene reaction. , 2004, Chemical communications.

[31]  P. C. Hariharan,et al.  The influence of polarization functions on molecular orbital hydrogenation energies , 1973 .

[32]  G. Vayssilov.  Structural and Physicochemical Features of Titanium Silicalites , 1997 .