Carbon dioxide capture is an effective method to mitigate climate change . Highly CO 2 -selective and highly moisture-resistant absorbent is essential for energy-efficient carbon capture by absorption. Herein, a highly CO 2 -selective and high-silica CHA zeolite in a pure lithium form (Li-SSZ-13) was synthesized using a direct synthesis method for the first time. The effects of gel n (SiO 2 )/ n (Al 2 O 3 ) ratio, gel n (SiO 2 )/ n (Li 2 O) ratio and synthesis time on the crystallinity , yield, micropore volume and CO 2 loading of the crystals were systematically investigated. The adsorption isotherms of CO 2 and N 2 were measured for directly synthesized Li-SSZ-13, conventional Na-SSZ-13 and ion-exchanged Li-Na-SSZ-13 zeolites. The dynamic breakthrough adsorption properties were measured for Li-SSZ-13 in comparison with Na-SSZ-13 and Li-Na-SSZ-13. The obtained Li-SSZ-13 exhibited a high CO 2 adsorption capacity of 4.48 mmol/g and a high CO 2 /N 2 IAST selectivity of 310 at 100 kPa and 273 K, which were 45.0 % and 441 % higher than Na-SSZ-13 zeolite, 24.8 % and 179 % higher than Li-Na-SSZ-13 zeolite, respectively. It suggests that directly synthesized Li-SSZ-13 zeolite has great potential for efficient CO 2 capture from flue gas .
High silica chabazite zeolite (CHA) is very important for selective catalytic reduction of NOx with ammonia (NH 3 -SCR), but its synthesis is time-consuming under conventional hydrothermal conditions (160 °C for 90–120 h). Herein, we report a novel strategy for highly efficient synthesis of CHA zeolite by means of fast crystallization at high temperatures in the absence of water solvent (240 °C for 1.5 h). X-ray diffraction, N 2 -adsorption isotherms, inductively coupled plasma, scanning electron microscopy, 29 Si and 27 Al MAS NMR, as well as thermogravimetry-differential thermal analysis suggest that the samples have high quality. This concept significantly enhances the space-time yields (STY) for CHA zeolite prepared from high-temperature synthesis in the absence of water solvent (almost two orders of magnitude higher than those of conventional hydrothermal synthesis). Moreover, compared with hydrothermal synthesis, the samples obtained from fast crystallization at higher temperatures (Si/Al = 12, 2.0% Cu loading) shows enhanced catalytic performance at 350–550 °C in NH 3 -SCR.
Yanpeng Chen,Rongshu Zhu,Guanyu Chen,Minghu Zhao,Min Ju,Rongming Cai,Jinqiang Gao,Mei Hong,Shihe Yang
Synthesis of small-pore chabazite (CHA) zeolites in the absence of organic structure-directing agents (OSDA) has been proven difficult. A judicious mixed cation approach recently reported could expand the design space of CHA formation. In a seemingly opposite direction, we herein report an anion tuning approach for controlling the zeolite polymorphism in an OSDA-free system that effectively promotes hierarchical CHA formation in a competitive growth with MER. Phenoxide media, utilizing mild in-situ nucleophilic etching in cooperation with zeolite framework growth, allow beneficial kinetic control to facilitate CHA nucleation. Operando analyses reveal the crucial role of stabilized dimeric aluminate species as a key intermediate for CHA phase selection. The phenol-mediated CHA zeolites exhibit almost perfect 9 molecules per unit cell CO 2 uptake capacity and no CH 4 adsorption. This work offers an anion tuning strategy for controlling zeolite polymorphism as a supplement to the current phase-selection toolbox that utilizes mixed inorganic cations.
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