Preparation of Mesoporous Silica Uniformly Coated with Titania and Its Application to Hydrodesulfurization Catalyst

摘要

Titania coating of mesoporous silicas (MSs) with different pore size was performed several times under thoroughly dried circumstances. When the pore size was 3 nm, the pore-plugging took place by only one time coating. On the other hand, for the pore size of 7 nm, a uniform coating with titania layer could be achieved until three time coating, and for that of 10 nm, the uniform coating without pore-plugging was obtained even after five time coating. These observations could be explained by the difference in the curvature of the silica pore walls. From various analyses and characterization, it was found that the titania coating was uniform and that three time coating was needed to coat all the silica walls and then possible coating mechanism was proposed. The MSs coated with titania were applied as the support of Mo catalyst for hydrodesulfurization (HDS) of sulfur-containing aromatics. The effect of titania coating on the dibenzothiophene HDS was not significant, but positive increase in activity was observed for 4,6-dimethyldibenzothiophene HDS. This increase was due to the enhancement of hydrogenation ability, in agreement with the results from the naphthalene hydrogenation. Moreover, it was found the formation of three-dimensional pores is very useful to increase the HDS activity.%チタンアルコキシドを原料とし.細孔径カ*異なるメソポーラスシリカのチタ二アコ一ティングを徹底的に水分を除去した条件下で数回 行った。細孔径が3 nmの場合.1回のコーティングで細孔閉塞が起きた。一方,7 nmでは3回のコーティングまで.10 nmでは5回コーティングでも細孔の閉塞は見られなカゝつた。このような違いは.シリカ壁の湾曲率の違いで説明することができた。種々の分析およびキヤラクタリゼーシヨンから，チタニアはシリカ細孔内に均一に分布し3回コーティングを行う事で.細孔全体を覆うことがわかった。そして.チタニア膜形成機構を提案した。このようにして調製したチタ二アコ一ティングメソポーラスシリカを担体とし.モリブデンを担持した触媒の脱硫活性を評価した。ジベンゾチォフェンの脱硫にぉレ、ては.チタ二アコ一ティングの影響力s見られな力1つたが，4,6 —ジメチルジベンゾチォフェンに対しては高い脱硫活性を示した。これは.チタニァコーティングにより触媒の水素化活性が向上したためで，ナフタレンの水素ィ匕実験結果と一致した。更に.メソポーラスシリカ細孔を三次元化することで.脱硫活性を飛躍的に向上することができた。