The structural origins of superior performance in sol-gel catalysts

Soft Matter

Volumn 1, Issue 3, 2005, Pages 231-237

  Ciriminna, Rosaria ^a   Ilharco, Laura M ^b   Fidalgo, Alexandra ^b   Campestrini, Sandro ^c   Pagliaro, Mario ^a  

^a CNR   (Italy)

^b INSTITUTO SUPERIOR TÉCNICO   (Portugal)

^c UNIVERSITY OF PADOVA   (Italy)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 26244434533     PISSN: 1744683X     EISSN: 17446848     Source Type: Journal    
DOI: 10.1039/b506021b     Document Type: Article

References (36)

1. For a recent review on the topic, see: R. Ciriminna and M. Pagliaro, Curr. Org. Chem., 2004, 8, 1851.
2. M. T. Reetz, P. Tielmann, W. Wiesenhofer, W. Konen and A. Zonta, Adv. Synth. Catal., 2003, 345, 717.
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7. A. Adima, J. J. E. Moreau and M. Wong Chi Man, Chirality, 2000, 12, 411.
8. Sol-gel organic-inorganic hybrid silica gels doped with chiral complexes are commercialised with the trademark CTIS-CACHy (Chiral Technologies Interface System - Catalytic Asymmetric CyanoHydrin) by the British fine chemicals manufacturer Avecia upon licensing of the sol-gel technology from Johnson Matthey. These catalysts allow efficient heterogeneous conversion of aldehydes and ketones into chiral cyanohydrins, high value building blocks and useful pre-cursors for hydroxyamino acids and amino alcohols.
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10. Pioneering work on catalysis by aerogels and xerogels was carried out by the team of Teichner at Lyon's University starting in the mid 1970s. For an account on some of the most interesting (photochemical) applications, see: M. Formenti and S. J. Teichner, Heterogeneous Photo-Catalysis, in Catalysis, A Specialist Periodical Report, eds. C. Kemball and D. A. Dowden, The Chemical Society, London, 1978, pp. 87-106.
11. Functionalized silica gels are commercial functional materials with a rapidly growing market. Doped silica gels offer several technical advantages over well-known organic resins being solvent-independent (rigid porous structure and no swelling), no non-specific binding, and with an high density of functional groups (small volume of gel required). Silica works in all solvents (organic and aqueous), is easy to weigh and handle, mechanically stable and prone to scale-up. A variety of functionalized silica gels are commercialized by the Canadian company SiliCycle Inc. See also the URL: http://www.silicycle.com/ .
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14. 2;
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16. Photo courtesy of Prof. Anthony Barrett. The picture refers to a polystyrene-supported metallocene prepared as described in: A. G. M. Barrett and Y. R. de Miguel, Chem. Commun., 1998, 2079.
17. -1 calculated assuming full accessibility of the Ru active centers in the Ormosil matrix, as described in: R. Ciriminna, S. Campestrini, M. Carraro and M. Pagliaro, Adv. Funct. Mater., 2005, 15, 846.
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19. (a) A double yield of the desired reaction product (from 31 to 62% in the case of chloramphenicol) and half of unselective cleavage product (from 37% to 20%) are typical, as reported in: M. L. Testa, R. Ciriminna, C. Hajji, E. Zaballos Garcia, M. Ciclosi, J. Sepulveda Arques and M. Pagliaro, Adv. Synth. Catal., 2004, 346, 655.
20. Typically, while the homogeneous oxidation of an aromatic diol yields 24% of α-hydroxy acid, the heterogenous oxidation using a 100% methyl-modified silica xerogel doped with TEMPO leads to an inversion of selectivity with an acid-ketone ratio of 60 : 40, as reported in: (b) P. Gancitano, R. Ciriminna, Alexandra Fidalgo, M. Ilharco Laura, M. L. Testa and M. Pagliaro, Org. Biomol. Chem., 2005, 3, 2389.
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26. (b) R. Abu-Reziq, D. Avnir and J. Blum, Angew. Chem., Int. Ed., 2002, 4, 4132.
27. The differences in the degree of crosslinking between Ormosils and silica gels derived from pure TMOS in fact are small: M. T. Reetz, Adv. Mater., 1997, 12, 943.
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30. The relative intensity of the 2θ ∼ 8° peak increases as the glass becomes more organically modified due to the increase in the structure long range order, as explained in: (a) S. L. B. Lana and A. B. Seddon, J. Sol-gel Sci., 1998, 13, 461.
31. For a brilliant X-ray structural analysis of Ormosils, see also: (b) P. W. Schmidt, D. Avnir, D. Levy, A. Hoehr, M. Steiner and A. Roell, J. Chem. Phys., 1991, 94, 1474.
32. Geometrical imperfection of the surface is a major contributor to the many applications of sol-gel porous materials due to the variability in the accessibility of the dopant to external reagents through the complex geometry of the pore network. For a thoughtful reflection on the role of imperfection in materials chemistry, see: D. Avnir, in The History of Colloid and Surface Chemistry in Japan, ed. K. Sakamoto, The Chemical Society of Japan, Tokyo, 2001, p. 16-17.
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35. B. M. Choudary, M. Lakshmi Kantam and P. Lakshmi Kantam, Catal. Today, 2000, 57, 17.
36. For a thorough analysis of the economic and social relevance of catalysis, see the report Catalytic Process Technology, National Academies Press, Washington, 2000; freely available at the URL: http://www.nap.edu/ catalog/10038.html (last time accessed: June 25, 2005).