Keiko A. Koyano

Investigation of the factors influencing the structural stability of mesoporous silica molecular sieves

Abstract Structural stability of mesoporous molecular sieves synthesized under various conditions were investigated. The effect of synthesis temperature, compositions, and silica source was examined. The MCM-41 synthesized from fumed silica and FSM-16 synthesized from kanemite was the most stable towards water, retaining the regularity for more than 90 days; the sample synthesized from TEOS at room temperature was less structurally stable. It is considered that the regularity loss involves the adsorption of water onto the surface silanol groups, which causes the nearby Si–O–Si bond cleavage, eventually resulting in the structural collapse. The X-ray powder diffraction, N 2 adsorption, and NMR study revealed that the structural stability has a strong correlation with the ratio of pore wall thickness t to the amount of SiOH, while such stability is weakly correlated with each parameter.

Vapour phase Beckmann rearrangement of cyclohexanone oxime catalysed by H? zeolite

when hexan-1-ol was used as the diluent in the vapour phase Beckmann rearrangement of cyclohexanone oxime, Hβ zeolite gave 100% conversion of the oxime with Iµ-caprolactam selective close to 96%.

Mechanical Stability of Mesoporous Materials, MCM-48 and MCM-41

The structural collapse of mesoporous molecular sieves, MCM-48 and MCM-41 materials by mechanical compression was found to occur mechanochemically through hydrolysis of Si–O–Si bonds. Their ordered structures were retained by compressing the well-dried samples under dry N2. Trimethylsilylation of mesoporous materials proved effective in eliminating their instability to compression through enhancing hydrophobicity.

Effect of potassium on the catalytic activity of TS-1

Titanium silicate-1 (TS-1) samples contained a significant amount of potassium derived from contaminants in an aqueous solution of Pr4NOH. By washing with H2SO4, the alkali-exchanged sites were converted to sites with two OH groups or ‘closed’ Ti(OSi)4 sites. Treatment of the acid-washed samples with an aqueous solution of K2CO3 led to the incorporation of potassium with a K/Ti ratio of around unity, suggesting that K ion exchange on TS-1 corresponds to the presence of Ti in the framework. The potassium ion exchange is considered to occur mainly on the Si–OH group adjacent to the ‘open’ Ti site. The presence of potassium retarded the oxidation of organic compounds with aqueous H2O2 to a different extent depending on the substrates. The retarding effect decreased in the order hexane>2-hexene>2-penten-1-ol and there was little inhibition in the oxidation of 2-penten-1-ol. This could be interpreted in terms of polarities of substrates and active sites in TS-1; non-polar hexane was less easily accessible to the Ti environment made more polar by adjacent potassium. In a similar manner, promotion of the oxidation of the alcoholic group in the reaction of 2-penten-1-ol over the K-type TS-1 might be ascribed to increased interaction of the alcoholic group with the active Ti site.

Remarkable activity enhancement by trimethylsilylation in oxidation of alkenes and alkanes with H2O2 catalyzed by titanium-containing mesoporous molecular sieves

Titanium-containing mesoporous materials, Ti-MCM-41 and Ti-MCM-48, have been successfully modified by trimethylsilylation to exhibit enhanced catalytic activity in the oxidation of alkenes and alkanes with H2O2.

Synthesis of titanium-containing mesoporous molecular sieves with a cubic structure

A titanium-containing mesoporous material with a cubic structure, Ti-MCM-48, is synthesized by a two-stage hydrolysis method using tetraethylorthosilicate and tetrabutylorthotitanate and found to be more active than Ti-MCM-41 in the epoxidation of bulky alkenes using H2O2.