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1. Concept of This Work

Shape Selective Adsorption Property of Molecular Sieving Silica Overlayer Prepared by Chemical Vapor Deposition Using Organic Template on Tin Oxide Naonobu Katada, Shohei Yamakita and Miki Niwa. CO 2 , H 2 O. CHO. CN. -. O. O. 1. Concept of This Work. Backgrounds Niwa et al. found:

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1. Concept of This Work

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  1. Shape Selective Adsorption Property of Molecular Sieving Silica Overlayer Prepared by Chemical Vapor Deposition Using Organic Template on Tin Oxide Naonobu Katada, Shohei Yamakita and Miki Niwa CO2, H2O CHO CN - O O 1. Concept of This Work Backgrounds Niwa et al. found: 1. Chemisorption of such an aldehyde as benzaldehyde on weakly basic metal oxide surface to form carboxylate anion. 2. CVD of Si(OCH3)4 forms a layer of silica with a homogeneous thickness on an atomic dimension. By combining these facts...... Si(OCH3)4 Reaction Cavity Catalytic Function Sensing Function + Molecular Sieving Property O2 NH3 SiO2 layer SnO2 etc.

  2. 2. Background CHO CHO - - O O O O Adsorption Capacity 0.50 nm-20.004 nm-2 Very early attempts using silica to construct a cavity Poljakov (1931), Dickey (1949) Organic template -- Sodium silicate Development of molecular imprinting on organic polymers Wulff (1972-) Molecular imprinting on inorganic surface Morihara (1988) Hydrolysis of SiO2 gel surface after Al doping in the presence of organic template (Footprint catalyst) Si alkoxide deposition / organophosphoric acid-adsorbing silica -> P/SiO2 Heilmann (1994) CVD of molecular-sieving SiO2 layer using aldehyde template on SnO2 Kodakari, Katada and Niwa (1995) CVD of SiO2 on organophosphoric acid-adsorbing Al2O3 Suzuki and Iwasawa et al. (2002) CVD of dense SiOSi network accelerated by CH3COOH Katada, Akazawa and Niwa, Adv. Mater., CVD,10, 103 (2004) However, the observed selectivity in adsorption property or catalysis was not high, and therefore not clearly due to the shape of cavity.

  3. 3. Aim of This Study Cl Cl CHO CHO CHO CHO Cl CHO BA 1-NA 4-CBA3-CBA2-CBA parametaortho Chemisorption experiments How precisely does the silica layer detect the molecular shape?

  4. 4. Experimental Measurements of Chemisorption Capacity Preparation 1. SiO2/SnO2 0.02 g 2. Aldehyde at 573 K 3. NH3 at 673 K 4. Formed nitrile was analyzed 1. SnO2 (20 m2 g-1, 0.1 g) 2. Benzaldehyde at 423 K 3. Si(OCH3)4 | CH3COOH/H2O | Si(OCH3)4 at 473 K 4. NH3 at 673 K, Benzonitrile was analyzed: No. of cavities 5. O2 at 673 K GC

  5. 5. Results (1) Effect of Template Cl Cl Cl Cl CO2- CO2- CO2- CO2- CO2- CHO CO2- CHO CO2- CHO Cl CHO CHO Template Surface density / nm-2 of Si atoms BA 4-CBA3-CBA2-CBA1-NA para meta ortho no 0 (pure SnO2) 2.1 0.641.30.281.1 no 5.7 (0.5 ML) 0.40 0.320.320.210.06 no 34 (3 ML) 0.01 0.000.000.000.00 Cavities BA5.7 (0.8 ML)0.480.510.550.180.00 0.00 1-NA 5.7 (1 ML) 0.43 0.310.310.39 0.22 0.32 All the tested aldehydes were well adsorbed on the SnO2 surface. The aldehydes were not adsorbed on the SiO2 surface. No selectivity was observed unless template was used. The selectivity was observed on SiO2/SnO2 prepared using BA template; only one Cl atom at the ortho position was detected;the selectivity was 100%. All the tested aldehydes were adsorbed on SiO2/SnO2 prepared using 1-NA template, showing that the selectivity was controlled by the molecular shape of template.

  6. (2) Thickness of Layer Cl Cl CHO CHO CHO Cl CHO Template: BA not suppressed 4-CBA para BA not suppressed 0 at 17 Si nm-2 3-CBA meta 0 at 6 Si nm-2 2-CBA ortho

  7. BA Template, Si 6 - 9 nm-2 SiO2, 1 ML Adsorption of 3-CBA (meta) Adsorption of 2-CBA (ortho) SnO2 BA, 4-CBA and 3-CBA ○ 2-CBA and 1-NA × at 6 nm-2

  8. BA Template, Si 17 - 20 nm-2 SiO2, 2 ML Adsorption of 3-CBA (meta) SnO2 BA, and 4-CBA ○ 3-CBA, 2-CBA and 1-NA × at 17 nm-2

  9. 6. Conclusion BAp-CBAm-CBAo-CBA1-NA SnO2○○○○○ SiO2-monolayer/SnO2××××× BA-SiO2 monolayer/SnO2○○○×× BA-SiO2 doublelayer/SnO2○○××× 1-NA-SiO2 monolayer/SnO2 ○○○○○ Selective adsorption precisely controlled by shape of template molecule and thickness of silica layer The selectivity was high (the adsorption of molecule larger than the template was not detectable). These were in good agreement with the molecular models.

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