Vanadosilicate mesoporous SBA-15 molecular sieves incorporated with N-alkylphenothiazines

被引:131
作者
Luan, ZH [1 ]
Bae, JY [1 ]
Kevan, L [1 ]
机构
[1] Univ Houston, Dept Chem, Houston, TX 77204 USA
关键词
D O I
10.1021/cm000318q
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Mesoporous silica SBA-15 molecular sieves have been incorporated with various amounts of vanadium via incipient-wetness impregnation with vanadium oxide triisopropoxide in hexane followed by calcination. The products (VSBA-15) have been characterized by nitrogen adsorption and diffuse reflectance UV-visible and electron spin resonance spectroscopies. The results show that the vanadium exists as isolated tetrahedral V5+ ions in dehydrated VSBA-15 with Si/V greater than or equal to 40 while vanadium chains develop as vanadium loading increases. Upon hydration a large fraction of the vanadium is transformed to square pyramidal and distorted octahedral V5+ ions by additional coordination to water molecules, suggesting an interior wall surface location for these V5+ ions. Upon CO reduction or incorporation of N-alkylphenothiazines (PCn), part of the V5+ is reduced to vanadyl VO2+ ions. While incorporation of PCn into VSBA-15 in the dark generates some PCn+ cation radicals, ultraviolet photoionization at room temperature further increases the yield for Si/V = 80 and 40. The PCn+ radicals are more stable in VSBA-15 than in siliceous SBA-15, and the photoyield increases with vanadium loading. The photoyield and stability of PCn+ also increase with increasing alkyl chain length of the N-alkylphenothiazines.
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页码:3202 / 3207
页数:6
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