Nangui Lv,Chenhu Sun,Xueqin Wang,Chan Wang,Yuanyuan Yue,Xiaojun Bao
Synthesizing CHA-type zeolite via template-free interzeolite transformation has been considered as a green method, but the resultant zeolite exhibits low activity in the selective catalytic reduction of NOx by ammonia (NH3-SCR). Herein we report a highly active NH3-SCR catalyst (Cu-CHAUSY) derived from CHA-type zeolite (CHAUSY) that is synthesized via template-free interzeolite transformation from ultra-stable Y (USY). The ultra-high activity is attributed to the specific silicon and aluminum configurations in USY which are distinctly different from those in the conventionally used parent NaY, although they have similar SiO2/Al2O3 ratios. This characteristic endows CHAUSY with more single Al atoms in a six-membered ring, benefiting the self-reduction of [Cu(OH)]+ and the activation of O2 during the NH3-SCR reaction. Moreover, Cu-CHAUSY is demonstrated to outperform the two reference catalysts prepared from the aluminosilicate gel by conventional hydrothermal crystallization with the assistance of organic templates. Our work provides a new strategy for preparing highly active NH3-SCR catalysts.
Hierarchically structured CHA-type zeolite composite was fabricated from industrial wastes red mud and coal fly ash via a facile two-step method without the addition of templates. A macro-porous ceramic support was first sintered, then zeolite/ceramic composite was formed through alkaline hydrothermal reaction. The physico-chemical properties of the samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and surface area analyzer (BET). It was found that the as-prepared zeolite/ceramic composite featured micron sized CHA-type zeolite particles (14.1 wt%) on the macro holes and channels of its ceramic support, which developed a hierarchical structure. Compared to the ceramic support, its specific surface area was increased by 2400%. The successfully made zeolite/ceramic composite was tested as an adsorbent for Cs(I) adsorption in batch mode. The results showed that the adsorption of Cs(I) on ZCC can be well described by the pseudo-first-order model and Langmuir model with the maximum adsorption capacity of 34.5 mg/g (25 °C), which is nearly 8 times that of ceramic support. The thermodynamic studies revealed an endothermic and spontaneous process. TCLP results showed that all targeted toxic metals met the regulatory standard. Thus, the reported hierarchically structured zeolite synthesized from industrial solid wastes, exhibiting high adsorption capacity of Cs(I) ions and good environmental compatibility, has the potential to be applied in wastewater treatment. Graphical Abstract
Preparation of Ceramic support using fly ash and red mud, then hydrothermal reaction to obtain Zeolite/ceramic composite, followed by cesium ion adsorption experiments to obtain the conclusion that the adsorption performance of zeolite/ceramic composite is much better than that of the Ceramic support.
Haiqian Lian,Eryue Song,Bin Bao,Wenhe Yang,Yu Yang,Yichang Pan,Shengui Ju
Metal-organic frameworks (MOFs) as molecular sieve membrane materials have received extensive attention on the gas separation application. However, the membrane separation performance is extremely limited by its intrinsic stability of frameworks. The successful preparation of high-quality gas separation membranes with excellent stability remains a grand challenge. ZIF-302 is based on hydrophobic ligand in-situ design with a high-stabile chabazite (CHA) topology. Herein, we synthesized uniform ZIF-302 nanocrystals with exceptional stability by introducing a modulator. Correspondingly, the continuous dense ZIF-302 polycrystalline membranes were also prepared for the separation of H 2 , N 2 , CO 2 , CH 4 and other gases. The permeance of H 2 and separation factor for H 2 /CH 4 mixtures at 35 °C and 1 bar were 2.8 × 10 -8 mol m −2 s −1 Pa −1 and 51.5, respectively, exceeding the Robeson upper bound in 2008. Furthermore, the separation performance of the super-hydrophobic ZIF-302 membranes for humidified mixed gases can maintain more than 168 h at 35 °C, indicating reliable long-term operational stability. Therefore, the CHA-type ZIF-302 polycrystalline membrane is promising for actual industrial gas separation.
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