这项工作介绍了通过使用聚二烯丙基二甲基氯化铵作为非表面活性剂中孔模板的水热法在框架内合成Pd负载的微孔钛硅沸石-1(Pd/TS-1)和Pd负载的分层钛硅沸石-1(Pd/HTS-1)。XRD,N2吸附,FT-IR,FESEM-EDX,TEM,XPS,和DR-UV技术用于表征合成材料的形态和理化性质。这些材料作为非均相催化剂进行了测试,连同四丙基溴化铵作为助催化剂,用于CO2与环氧化物的环加成反应以产生环状碳酸酯。发现环氧化物的转化率受催化剂的酸度和孔可及性的影响。使用Pd/HTS-1促进庞大的底物进入活性位点,导致比Pd/TS-1更高的转化率。对于至少五个连续的循环,获得超过85%的转化率,而催化活性没有显著损失。通过DFT计算进一步研究了Pd活性表面与表氯醇(ECH)之间的相互作用。与Pd(111)表面相比,Pd(200)的存在对吸附表氯醇(ECH)和随后形成解离的ECH(DECH)中间体的影响更大。然而,Pd(111)在增强DECH物种捕获CO2的活性方面占主导地位。因此,对于CO2与ECH的环加成,需要Pd(200)和Pd(111)表面的共存。
This work presents the synthesis of Pd-loaded microporous titanosilicalite-1 (Pd/TS-1) and Pd-loaded hierarchical titanosilicalite-1 (Pd/HTS-1) with abundant mesopores (2-30 nm) inside the framework via hydrothermal method using polydiallydimethyl ammonium chloride as the non-surfactant mesopore template. XRD, N2 sorption, FT-IR, FESEM-EDX, TEM, XPS, and DR-UV techniques were used to characterize the morphological and physicochemical properties of the synthesized materials. These materials were tested as heterogeneous catalysts, along with tetrapropylammonium bromide as co-catalyst, for cycloaddition reactions of CO2 with epoxides to produce cyclic carbonates. It was found that the epoxide conversions were influenced by acidity and pore accessibility of the catalysts. Using Pd/HTS-1 facilitated bulky substrates to access active sites, resulting in higher conversions than Pd/TS-1. Over 85 % conversions were achieved for at least five consecutive cycles without significant loss in catalytic activity. The interaction between the Pd active surfaces and epichlorohydrin (ECH) was further studied by DFT calculations. The existence of Pd(200) was more influential on adsorbing epichlorohydrin (ECH) and subsequent formation of dissociated ECH (DECH) intermediate than Pd(111) surface. However, Pd(111) was dominant in enhancing the activity of DECH species for capturing CO2. Therefore, the co-existence of Pd(200) and Pd(111) surfaces was needed for cycloaddition of CO2 with ECH.