The preparation of pure EUO zeolite under conventional conditions usually takes more than three days, limiting the application of the EUO zeolite. It is widely acquainted that the seed-assisted synthesis of zeolites without organotemplates is inexpensive, environmentally-friendly and lead to Al-rich products. However, synthesis with EUO seeds in the absence of organic-templates always leads to the formation of impurity phases. In this work, EUO zeolite (s-EUO) is successfully obtained by seed-directed synthesis without organotemplates. This is the first seed- directed synthesis of pure EUO zeolite with special Al source. Physicochemical characterization results show that the synthesized s-EUO zeolite exhibits high crystallinity and high specific surface area, and contains uniform crystals and plenty acidic sites. The s-EUO crystallization (by this method) occurs in a considerably shorter time (18 h) and in a more mild condition (160 °C, static state), compared to that of the conventional EUO zeolites (c-EUO, 72 h at 180 °C, at rotation) in the presence of organotemplate. Moreover, the catalytic performance of the H-form of the s-EUO zeolite is enhanced to that of the c-EUO zeolite for m-xylene isomerization, confirming the NH3-TPD results.
Li Chen,Jing Geng,Renhui Gao,Qianqian Xu,Zheng Guo
Metal oxide-based gas sensors encounter challenges in effectively detecting hazardous benzenes due to their stability and structural similarities. Here we report an innovative in situ growth method for synthesizing Fe 2 O 3 /Si-FeWO 4 heterostructure nanotubes (NTs) using highly negatively charged multivacant lacunary TBA 4 H 6 [SiW 9 O 34 ]·2H 2 O ( α -SiW 9 ) and Fe 3+ as precursors. A two-step process involving electrospinning followed by a thermal oxidation method was employed to synthesize a series of the uniform Si-FeWO 4 decorated Fe 2 O 3 heterostructure NTs. Considering the rich Fe 2 O 3 /Si-FeWO 4 active interfaces, rapid electron transfer, and high specific surface area, the optimal Fe 2 O 3 /Si-FeWO 4 based sensors demonstrate significantly higher sensitivity (S = 27.5) towards 50 ppm m-xylene in comparison to pristine Fe 2 O 3 (S = 1.8). Furthermore, the Fe 2 O 3 /Si-FeWO 4 exhibits excellent stability, humidity resistance, and high selectivity for m-xylene. This work offers an efficient, cost-effective strategy to synthesize Fe 2 O 3 /Si-FeWO 4 heterostructure NTs, with prospects for synthesizing other advanced sensing heterostructure nanomaterials with lacunary polyoxometalates as precursors.
Li Wang,Liyuan Li,Penggang Lv,Xin Gao,Yang Gao,Lu Han,Xuedong Zhu,Kake Zhu
A hierarchically structured ZSM-11/ZSM-5 intergrowth zeolite was generated using a polycationic organic structure-directing agent (OSDA), [-N+(CH2CH2CH2CH3)2-(CH2)8-]n[OH–]n, which is conceptually equivalent to bond-linked tetrabutylammonium (TBA), the frequently used OSDA for ZSM-11 synthesis. The produced ellipsoidal crystals have a major axis length of 130–240 nm and a minor axis length of 75–120 nm, made up of aligned nanocrystals of 44 to 83 nm, to construct an auxiliary macro- to mesopore network ranging from 45 to 80 nm. The Si/Al ratio can be manipulated from 50 to ∞, and the intergrowth exhibits acidity comparable to that of ZSM-5, which is distinct from previous reports that formation of hierarchical porosity or intergrowth often compromises the inherent acidity of zeolitic crystals. Such hierarchical architecture also endows the material with enhanced transport properties, as validated by 2-methylhexane adsorption measurements. In the catalytic methylation of meta-xylene with methanol, the hierarchical ZSM-11/ZSM-5 zeolite exhibited superior performance to that of ZSM-5, with enhanced activity and total trimethylbenzene and tetramethylbenzene selectivity, which was elevated from 28% to 39%. These catalytic merits stem from the combined effects of preserved acid strength, optimized pore connectivity, and alleviated diffusion limitations.
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