摘要
利用极稀悬浮液中蒙脱土的解离作用并结合柱化技术过程,制备了介孔结构的铝铁/蒙脱土复合材料(Fe-Al/mmt);并采用粉末X射线衍射、氮等温吸脱附、傅立叶红外光谱、紫外可见光漫反射光谱及苯酚催化羟基化反应表征了其结构和性能。结果显示,铁铝聚合前驱液中铁/铝比影响复合材料中蒙脱土的解离程度,且仅当低铁/铝比时(即Fe/(Fe+Al)物质的量的比介于0.05-0.3),嵌入解离的蒙脱土片层间的混合铁铝物种呈现能耐温350℃的热稳定性;氮等温吸脱附分析反映出这种解离的蒙脱土堆积结构呈现介孔特征,孔径分布窄,介于2.0-2.3nm;红外分析表明材料表面具有L酸和B酸位,并且L酸位量与嵌入解离的蒙脱土结构中的混合铁铝物种相关;由于结构中混合铁铝物种的存在及相应的Si-O→Fe、Al-O→Fe间的电子跃迁,Fe-Al/mmt材料在紫外区呈现宽泛的能量吸收特征。这些结果说明,由于混合铁铝物种嵌入于解离的蒙脱土片层堆积结构中,形成了“卡片屋”式介孔结构。实验条件下,Fe/(Fe+Al)物质的量的比为0.3的Fe-Al/mmt呈现较佳的催化羟基化性能,苯酚转化率为36.7%,二酚产物选择性32.3%;并且初步表明铝掺杂后,通过铁铝比和表面酸性的调整,材料的部分选择氧化性能可以得到改善。
Using delamination of the ultra dilute montmorillonite （mmt） suspension and pillaring techniques, the mixed Fe-Al/montmorillonite （Fe-Al/mmt） composites with mesoporous structure have been synthesized. Powder X-ray diffraction （XRD）, N2 adsorption-desorption isotherms, Fourier transform infrared spectroscopy （FTIR）, UV- Vis-diffuse reflectance spectroscopy （UV-Vis-DRS） and catalytic hydroxylation of phenol with H2O2 were used to characterize the samples. The XRD results suggest that the content of Fe plays an important role in the delami- nating degree of mmt owing to flocculation of Fe-Al polyoxycations precursors. Only under lower molar ratio of 0.05 to 0.3 of Fe/（Fe＋Al）, can Fe-Al/mmt composites with the intercalated and occluded mixed thermally stable Fe-Al oxide particles up to 350 ℃ be obtained. Accordingly, the nitrogen sorption isotherms of resulting samples are of mesoporous type with hysteresis loops and narrow pore size distribution. The FTIR spectra preliminarily show the synthesized Fe-Al/mmt composites contain both Bronsted and Lewis acid sites. Lewis acid sites could be mainly provided and adjusted by intercalated/occluded mixed Fe-Al species. The UV-Vis-DRS spectra indicate the occurrence of clay Si-O → Fe and Al-O → Fe charge transfer transitions and interband transitions, leading to the characteristic broad absorbance and confirming the formation of mixed Fe-Al oxide in mint aggregates. So it has been postulated that under experimental conditions, when the ultra dilute mint suspension was used, the flocculation of mmt by pillaring Fe-Al polyoxycations could lead to delaminated aggregates, the ＂card-house＂ structure occluding in mixed Fe-Al polyoxycations species. The catalytic activity of phenol hydroxylation was at a ratio of Fe/（Fe＋Al）=0.3 with phenol conversion of 36.7% and selectivity to hydroxylation products of 32.3%. The doping of alumina could improve the catalytic acidity. partial oxidation via adjustment of Fe/（Fe＋Al） ratio and the surfac
出处
《无机化学学报》
SCIE
CAS
CSCD
北大核心
2006年第4期617-624,共8页
Chinese Journal of Inorganic Chemistry
基金
国家自然科学基金(No.20541002)
浙江省自然科学基金(No.Y405064)
中国石油化工股份有限公司科技项目(No.X504034)。
关键词
蒙脱土
解离结构
介孔复合材料
柱化剂
苯酚羟基反应
montmorillonite
delaminating structure
pillaring precursor
mesoporous composites
phenol hydroxylation
