The SSZ-13 zeolite is an excellent catalyst for dewaxing hydrocarbon feedstocks and hydrocracking.ssz-13 zeolite It can be used in reforming reactions at higher temperatures and pressures, as well. Typical feedstocks include recycle petroleum fractions, liquefied coal, shale oil and tar sands. The feedstocks may contain metal ions or have low or high nitrogen and sulfur content. The SSZ-13 catalyst can be used in both a gas phase and a liquid phase.
The catalyst is available in the form of powder, granule or in a molded product such as extrudates with an organic binder. The molded material can be dried or semi-dry before extruding and can be used at ambient or subatmospheric pressures.
SSZ-13 has an Al-to-Si molar ratio of about 15:1. This makes it a very versatile aluminosilicate for a variety of applications. In many cases, it is combined with a porous matrix in the form of silica, alumina, titania, magnesia or mixtures thereof, in order to obtain more tailored properties. Moreover, the SSZ-13 aluminosilicate can be composited with various other materials such as ceramics and refractory oxides to provide multifunctional products.
In the context of the synthesis of SSZ-13, there is a need for innovative methods to improve the cost-effectiveness of the production process. The conventional synthesis, which requires the use of expensive and toxic N,N,N-trimethyl-1-adamantylammonium hydroxide (TMAdaOH) as an organic structure-directing agent and a slow hydrothermal crystallization process lasting more than four days, severely limits the cost-effectiveness of the resulting zeolite.
Regulating the framework Al atoms by pairing or isolation introduces remarkable catalytic or adsorptive diversity into compositionally similar SSZ-13 zeolites. This can be achieved by controlling the Si-Al distance and the symmetry of the resulting crystalline structures. In addition, the Si-Al distance can be modified to control the Bronsted acidity in a given zeolite material.
Cu-SSZ-13(3,4) materials exhibiting different Bronsted acidity have been prepared by altering the Si/Al ratio and the concentration of the sodium hydroxide solution. The FTIR transmission spectra of Cu2+ and Cu+oxo (Cu-oxo) species show that the variation in acidity is due to the positioning of the copper sites in the SSZ-13 framework, i.e. the sitting of the cations is controlled by the Al distribution in the SSZ-13 framework (Al pairs or single Al atoms).
In order to achieve faster and more reliable synthesis methods, it is important to understand how the chemistry of the SSZ-13 aluminosilicate affects its performance as a catalyst. This can be done using a combination of techniques such as thermodynamic modeling, SEM-EDX analysis and two-dimensional multiple quantum magic-angle spinning nuclear magnetic resonance (23Na MQ MAS NMR). These studies have revealed that the presence of Y ions stabilizes the tetrahedral Al sites in the SSZ-13 zeolite by forming a hybrid site. In addition, Y ions modify the Si-Al coordination geometry, thereby preserving the ion exchange capacity of the SSZ-13 zeolite. This is also supported by 27Al NMR and temperature-programmed desorption (NH3-TPD) measurements. This approach provides valuable insights into the synthesis of new and improved SSZ-13 zeolites with a desirable catalytic behavior, especially for the conversion of hydrocarbons.
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