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首页> 外文期刊>Journal of Materials Science >Mesoporous silica-aluminas derived from precipitation: a study of the acidity, textural properties and catalytic performance
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Mesoporous silica-aluminas derived from precipitation: a study of the acidity, textural properties and catalytic performance

机译：沉淀法制得的介孔二氧化硅-氧化铝：对酸度，质构性质和催化性能的研究

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Silica-alumina covering broad range of compositions have been obtained by combined hydrolysis precipitation. These materials were characterized mainly by solid-state NMR spectroscopy. Textural properties were investigated by measurements of nitrogen sorption, and the acidity of Bronsted sites was studied by TPD and FTIR spectroscopy using ammonia as probe molecule. The catalytic performance of these materials was studied by the Bronsted acid-catalyzed acetalization reaction. New insights into the nature of the silicate compartment and the acidity of Bronsted sites of amorphous silica-alumina have been obtained. Silica-aluminas of different silica content do not represent a homologous row. They differ mainly in the connectivity of the silicate compartment. The results show that silica-alumina contain a quantitative amount of Bronsted sites. The appearance of tetrahedral Al is closely related to silica. The concentration of tetrahedral Al, and hence Bronsted acid sites, follows a volcano shape. After increasing with SiO2 content, the site concentration reaches a maximum at 20 wt% of silica and decreases again due to the marked decrease in the total alumina content in high silica samples. Surprisingly, the catalytic activity does not follow this trend. It increases especially with high silica samples due to the interplay of acid site concentration and the strength of acid sites. The aluminosilicate compartment of high silica samples shows a high Si/Al ratio. The improved acid strength of the sites overcompensates the lower site concentration, leading to a distinctly enhanced catalytic activity.
机译：通过组合水解沉淀获得了覆盖范围广泛的二氧化硅-氧化铝。这些材料主要通过固态NMR光谱表征。通过测量氮的吸附来研究质地特性，并使用氨作为探针分子通过TPD和FTIR光谱研究布朗斯台德位点的酸度。通过布朗斯台德酸催化的缩醛化反应研究了这些材料的催化性能。已经获得了对硅酸盐隔室的性质和非晶硅铝氧化物的布朗斯台德位点酸度的新见解。不同二氧化硅含量的二氧化硅-氧化铝不代表同源行。它们的主要区别在于硅酸盐隔室的连通性。结果表明，二氧化硅-氧化铝包含一定数量的布朗斯台德位点。四面体Al的出现与二氧化硅密切相关。四面体Al的浓度以及布朗斯台德酸位的浓度遵循火山的形状。随着SiO2含量的增加，该位点浓度在二氧化硅的20 wt％处达到最大值，并由于高二氧化硅样品中总氧化铝含量的显着降低而再次降低。令人惊讶地，催化活性没有遵循这种趋势。由于酸性位点浓度和酸性位点强度之间的相互作用，尤其是在高二氧化硅样品中，它会增加。高二氧化硅样品的硅铝酸盐隔室显示出高的Si / Al比。这些位点的改善的酸强度过度补偿了较低的位点浓度，从而导致明显增强的催化活性。

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