AbstractThe surface of SBA‐15 mesoporous silica was modified by N‐hydroxyphthalimide (NHPI) moieties acting as immobilized active species for aerobic oxidation of alkylaromatic hydrocarbons. The incorporation was carried out by four original approaches: the grafting‐from and grafting‐onto techniques, using the presence of surface silanols enabling the formation of particularly stable O−Si−C bonds between the silica support and the organic modifier. The strategies involving the Heck coupling led to the formation of NHPI groups separated from the SiO2 surface by a vinyl linker, while one of the developed modification paths based on the grafting of an appropriate organosilane coupling agent resulted in the active phase devoid of this structural element. The successful course of the synthesis was verified by FTIR and 1H NMR measurements. Furthermore, the formed materials were examined in terms of their chemical composition (elemental analysis, thermal analysis), structure of surface groups (13C NMR, XPS), porosity (low‐temperature N2 adsorption), and tested as catalysts in the aerobic oxidation of p‐xylene at atmospheric pressure. The highest conversion and selectivity to p‐toluic acid were achieved using the catalyst with enhanced availability of non‐hydrolyzed NHPI groups in the pore system. The catalytic stability of the material was additionally confirmed in several subsequent reaction cycles.
摘要用 N-羟基邻苯二甲酰亚胺(NHPI)分子修饰 SBA-15 介孔二氧化硅的表面,使其成为烷基芳烃有氧氧化的固定活性物质。采用了四种独创的方法:从接枝和从上接枝技术,利用表面硅烷醇的存在,在二氧化硅支架和有机改性剂之间形成特别稳定的 O-Si-C 键。采用赫克耦合的策略可形成 NHPI 基团,并通过乙烯基连接体与二氧化硅表面分离,而采用接枝适当的有机硅烷耦合剂的改性方法则可使活性相不含这种结构元素。傅立叶变换红外光谱和 1H NMR 测量验证了合成过程的成功。此外,还从化学成分(元素分析、热分析)、表面基团结构(13C NMR、XPS)、孔隙率(低温 N2 吸附)等方面对所形成的材料进行了研究,并将其作为常压下对二甲苯有氧氧化的催化剂进行了测试。使用孔隙体系中非水解 NHPI 基团可用性增强的催化剂,对甲苯酸的转化率和选择性最高。此外,该材料的催化稳定性在随后的几个反应循环中也得到了证实。