SSZ-13 ZeoliteOct 09, 2018 | ACS MATERIAL LLC
SSZ-13 molecular sieve is prepared by the hydrothermal method with silica sol, aluminium sulphate, sodium hydroxide and deionized water as raw materials, and N, N, N-trimethyl-l-adamant ammonium hydroxide as a template. Due to its specific surface area and distinctive eight-membered ring structure, SSZ-13 shows good applicability in separating N2 from CO2 in flue gas streams. Cation exchanged SSZ-13 can yield higher separation efficiency and it can also be used as a good catalyst in NH3 selective catalytic reduction (NH3-SCR), propylene production from ethylene, and methanol-to-olefins (MTO) reactions.
The different types of molecular sieves are defined by the International Zeolite Association (IZA) by different structure codes, such as FAU, MFI, BEA and CHA. SSZ-13 is a type of zeolite with CHA topology, which was first disclosed in the 1980s by Stacey I Zones (1985, US 4544538). The structure of SSZ-13 consists of a 3D elliptic network of orderly arranged eight-membered rings with strictly alternating AlO4 and SiO4 tetrahedrons interconnected with oxygen bridges (Figure 1).1 The channel size of SSZ-13 is 0.38 nm,2 and its specific surface area is about 550 m2/g~700 m2/g. It is classified as a member of micropore zeolites based on the channel size.
Figure 1. The structure of SSZ-13 zeolites1
SSZ-13 may be used as an adsorbent (an air-purifying agent, for example) or catalyst (automobile exhaust catalyst, for example) due to the excellent thermal stability resulting from its large specific surface area and distinctive eight-membered ring structure.3 The presence of AlO4 and SiO4 tetrahedrons in the framework results in cation exchange and acidity adjustability, which in turn makes SSZ-13 exhibit good catalytic behaviour.4 SSZ-13 has been applied in the catalytic cracking and hydrocracking of hydrocarbon compounds, as well as reactions of olefins and aromatics. By altering the Si/Al ratio, the nature of extra-framework cations as well as particle size, adsorption and catalytic properties of SSZ-13 can be improved and modified.
SSZ-13 molecular sieve is prepared by the popular hydrothermal method with silica sol, aluminium sulphate, sodium hydroxide and deionized water as raw materials, and N, N, N-trimethyl-l-adamant (TMMA+) ammonium hydroxide as a template. SiO2, A12O3, Na2O and H2O are first mixed with different molar ratios, the mixture is stirred at room temperature for 0.5 h then poured into a PTFE-lined high-pressure reactor, and crystallized at 155 ℃ for 2~5 days. The SSZ-13 molecular sieve is then prepared by pouring the obtained crystal into a beaker, heating it to 70~80℃, drying the separated crystal at 120℃ after three cycles of ion exchange with a certain amount of ammonium chloride for 2 hours followed by vacuum filtration. The final step is to remove the template and water from the crystal by temperature-programmed calcinations. SSZ-13 molecular sieves with different SiO2/Al2O3 molar ratios can be obtained on our ACS Material online store.
Furthermore, other raw materials for the synthesis of SSZ-13 molecular sieves are also feasible. For example, silicon-containing compounds can be used from silica sol, silica gel, tetraethyl orthosilicate. Aluminium-containing compounds can be used from aluminium oxide, pseudo-boehmite, aluminium hydroxide, aluminium sulphate and etc. The template can be used from N, N, N-trimethyl-l-adamant ammonium hydroxide, benzyl trimethyl ammonium hydroxide and their mixture5. Figure 2 exhibits the standard XRD patterns of the SSZ-13 molecular sieve reported by International Zeolite Association (IZA). It indicates that the prepared crystal is a SSZ-13 molecular sieve without any mixed crystal.
Figure 2. XRD spectra of SSZ-13 molecular sieve
SSZ-13 (CHA) zeolites have gained a greater reputation over other zeolites for their high affinity toward carbon dioxide over other gases due to its unique pore structure and arrangement of cations in the framework. Increasing the electrostatic interaction between the framework and the CO2 guest molecules by altering the Si/Al ratio, the nature of extra-framework cations, as well as the particle size, can improve adsorption properties. Such alterations make these zeolites excellent molecular sieves capable of separating CO2 (3.3Å) from N2 (3.6Å) in flue gas streams6. Additional modifications involving the use of larger cations, such as potassium and cesium in low silica CHA, were found to yield even higher selectivity of CO2 over N2. Specifically, the location and quantity of cations in the pores of SSZ-13 will be correlated to differences in adsorption of CO2 vs N2 via breakthrough experiments.
In addition, SSZ-13 has also received significant attention due to its excellent catalytic performance in the NH3 selective catalytic reduction (NH3-SCR), propylene production from ethylene, methanol-to-olefins (MTO) catalysis7,8.
SSZ-13 zeolites have received significant attention due to their excellent capacity for CO2 adsorption and separation. Furthermore, the properties of its catalytic performance in the NH3-SCR and MTO reaction are crucial for guiding the design of better and more advanced SSZ-13 catalysts in the future.
ACS Material Products:
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methanol-to-olefins catalysis by using nanometer accuracy by stochastic chemical reactions fluorescence microscopy and positron emission profiling.” ChemCatChem, vol. 9, no. 2, 2017, pp. 3470-3477, DOI: 10.1002/cctc.201700567
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