【摘要】：苯乙烯側鏈C=C的選擇性氧化一直是烯烴環(huán)氧化研究領域關注的熱點之一.近幾十年來,苯乙烯環(huán)氧化研究主要集中于多相過渡金屬催化劑的開發(fā)與應用;以銅為主要活性物種的催化劑因具有較高的環(huán)氧苯乙烷選擇性而備受矚目.然而,采用pH調節(jié)法將銅離子引入三維六方介孔材料KIT-6陣列尚未見報道,尤其是pH值對合成材料的形貌、結構以及催化活性的影響尚未可知.基于此,本文采用pH調節(jié)法合成了銅嵌入KIT-6介孔材料Cu-KIT-6x(x代表初始溶膠的pH值,x=1.43,2.27,3.78,3.97,4.24,6.62),并將其應用于苯乙烯環(huán)氧化反應.采用X射線粉末衍射、氮氣吸附脫附、透射電子顯微鏡以及X射線光電子能譜等手段對Cu-KIT-6x的表面結構及形貌進行了細致表征.結果表明,隨著pH的變化,Cu-KIT-6x催化劑的物理特性、表面結構尤其是銅物種種類和含量均變化較大.較低的pH導致銅物種主要以Cu~(2+)形式存在,難以引入到KIT-6骨架中,且不利于介孔材料的合成,最終導致產(chǎn)生無序介孔結構.當pH增大到3.78時,約有4.6 wt%的Cu(Ⅱ)以 Cu O Si 形式成功引入KIT-6骨架中,獲得了具有較高比表面積且有序的孔結構.此外,由于Cu~(2+)的引入,骨架內部分Si~(4+)被取代,促使Cu-KIT-6_(3.78)擁有可與載體KIT-6相媲美的大孔徑.然而,當pH繼續(xù)增大時,過量的Cu~(2+)從KIT-6骨架中析出,以CuO形式存在于載體表面,從而導致Cu-KIT-6的孔徑逐漸增大;同時NaOH對三維立方介孔結構的破壞,使得介孔結構坍塌及比表面積顯著降低.以苯乙烯環(huán)氧化反應評價了Cu-KIT-6x系列催化劑的催化活性.當以叔丁基過氧化氫為氧化劑,乙腈為溶劑,在70 ℃反應6 h后,Cu-KIT-6_(3.78)表現(xiàn)出最優(yōu)的苯乙烯轉化率(43.5%)及環(huán)氧苯乙烷選擇性(86.6%).使用4次后,Cu-KIT-6_(3.78)展示了穩(wěn)定的苯乙烯轉化率、環(huán)氧苯乙烷選擇性及有序的孔結構,充分表明其具有出色的穩(wěn)定性.各表征結果揭示了在適宜pH下合成的Cu-KIT-6_(3.78)催化劑具有較高的銅含量、有序的立方Ia3d介孔結構及合適的結構參數(shù),因而在苯乙烯環(huán)氧化反應中表現(xiàn)優(yōu)異活性和良好穩(wěn)定性.
[Abstract]:Selective oxidation of side chain C of styrene has been one of the hot topics in the field of epoxidation of olefin. In recent decades, the epoxidation of styrene has focused on the development and application of polyphase transition metal catalysts, and the catalyst with copper as the main active species has attracted much attention for its high selectivity to epoxy-phenylethane. However, the introduction of copper ions into KIT-6 arrays of three-dimensional hexagonal mesoporous materials by pH adjustment method has not been reported, especially the effect of pH value on the morphology, structure and catalytic activity of the synthesized materials. Based on this, the copper intercalated KIT-6 mesoporous material Cu-KIT-6x (x representing the pH value of the initial sol) was synthesized by pH adjustment method and applied to the epoxidation of styrene. The surface structure and morphology of Cu-KIT-6x were characterized by X-ray powder diffraction, nitrogen adsorption and desorption, transmission electron microscopy and X-ray photoelectron spectroscopy. The results show that the physical properties of Cu-KIT-6x catalyst vary with the change of pH, and the surface structure, especially the species and content of copper species change greatly. Due to the low pH, copper species mainly exist in the form of Cu~ (2), which is difficult to be introduced into the framework of KIT-6, and is not conducive to the synthesis of mesoporous materials, resulting in the formation of disordered mesoporous structure. When pH increased to 3.78, about 4.6 wt% Cu (鈪，

本文編號：2248702