Molecular Sieving Silica Overlayer on γ-Alumina:  The Structure and Acidity Controlled by the Template Molecule

Abstract

A silica overlayer was prepared on γ-alumina by a method of chemical vapor deposition (CVD) of silicon alkoxide using preadsorbed benzaldehyde and R-naphthaldehyde as a template. Infrared spectroscopy confirmed that the preadsorbed benzoate anion species remained after the deposition of silica, indicating that silica was deposited on the exposed surface of alumina. On the basis of the adsorption property of modified alumina, it is considered that the silica overlayer had a vacancy whose size was as large as the template molecule. 29 Si NMR spectroscopy showed that the Si species deposited using the template was Si(OAl)1(OSi)1(OH)2 or Si(OAl)2(OSi)1(OH)1, while the deposition without the template formed such a species as Si(OAl)1(OSi)3 and Si(OAl)1(OSi)2(OH)1 bonded via a two-dimensional siloxane network. Lack of activity for double-bond isomerization of 1-butene to 2-butene on the silica overlayer prepared using the template was consistent with the previous results that the two-dimensional network of siloxane on the alumina surface induced Brønsted acidity on the Al-O-Si-OH species. Both the adsorption and acidic properties on silica-deposited alumina using R-naphthaldehyde were different from those on the sample prepared using benzaldehyde, showing that the structure of the silica overlayer was controlled by the template molecules.

Molecular-Imprinted Metal Complexes for the Design of Catalytic Structures

“…22.5). Silicate sources have been utilized to grow thin layers of SiO 2 onto oxide surfaces in a layer-by-layer fashion [85][86][87]. The Si(OCH 3 ) 4 precursor reacts with surface silanol groups preferentially, and polymerization does not occur in the absence of surface silanols.…”

Alcóxidos como precursores na síntese de novos materiais através do processo sol-gel

“…Os estudos em grande parte enfocam a síntese de materiais de composição mista, cuja representação dos óxidos formados é simplesmente indicada apenas pela participação dos metais que entraram na formação dos mesmos. Por exemplo, no processo sol-gel envolvendo os alcóxidos para produzir óxidos mistos, os mesmos são denominados por Zr-Ti, Al-Ti etc [75][76][77][78][79][80][81][82][83][84][85][86][87] . As propriedades físico-químicas de óxidos mistos, como por exemplo Zr-Si, têm despertado enorme interesse pelo fato de que a nova composição apresenta elevada estabilidade térmica e química, além de que a superfície dispõe de grupos OH, responsáveis pela elevada acidez.…”

Silica-Tin Oxide Sensor with Molecular Recognition Ability

“…The so-prepared SiO 2 /Al 2 O 3 also showed shape-selective adsorption behavior. In addition, the solid acidity was precisely controlled by changing the microstructure [51]. …”

“…The deposited silicon density was 2.9 (a), 4.8 (b), 10.6 (c), and 6.0 Si nm -2 (d). Reproduced with permission from [51], © American Chemical Society. thick), in which two platinum wires had been buried.…”