Synthesis of Mordenite Using Multiple Organics
This invention establishes a novel synthetic route for the preparation of zeolite mordenite (MOR) materials with reduced internal pore length. Mordenite is used in a wide range of applictoins that includes catalytic reactions such as alkylation, isomerization, and carbonylation, among others. Prior studies have confirmed that the catalytic activity of this framework is facilitated by side pockets created at the intersection of 8-membered ring (MR) channel with 12-MR channels; however, the efficacy of MOR catalysts is often limited by suboptimal properties, such as large crystal size (ca. 5-20 ï�m), low silicon-to-aluminum ratio (SAR < 10), and the presence of crystal impurities. One of the challenges associated with conventional MOR catalyst is short lifetime. To this end, we have identified a novel technique to synthesize MOR crystals with dimensions less than 100 nm.
The synthesis method relies on the use of two or more organics. For example, we use N, N, N-trimethyl-1-1-adamantammonium (TMAda) in combination with at least one alcohol (e.g., 1,2-hexandiol, D61,2) in the growth solution which has hydrophobic alkyl tail and hydrophilic hydroxyl functional group. When using a combination of both organics at a suitable ratio (for example, TMAda with excess D61,2), we obtain MOR nanosheets with an average thickness of 60 – 80 nm along the c-axis (i.e., in the direction of the one-dimensional 12-MR channels). When growth mixtures are prepared using TMAda as the sole organic, the final product is zeolite CHA (SSZ-13). In the absence of any organic or in the presence of only alcohols, the final product is zeolite MFI (ZSM-5). This indicates that the presence of both organics is necessary for the formation of MOR nanosheets.
Zeolite crystal size can impact catalyst lifetime by providing either short or long residence times (i.e., diffusion path length within the pores). Longer residence time tends to favor the formation of carbonaceous deposits (i.e., coke) that deactivates catalysts. The invention we propose here allows for more than two orders of magnitude reduction in the length of MOR channels, leading to nanosheets with dimensions in the range of 60-100 nm. Comparisons of these materials with conventional MOR catalysts reveals an approximate two-fold increase in lifetime (e.g., for tests using cumene cracking as a model reaction).
Another advantage of this method is the increased silicon content in the final MOR crystalline product. Conventional syntheses of MOR results in materials with a Si/Al molar ratio of ca. 7. The MOR nanosheets have an average Si/Al ratio of 10. Collectively, we show that the combination of at least two organics can alter the physicochemical properties of zeolite MOR crystals in ways that are more beneficial to applications in catalysis and possibly others (e.g., adsorption, separations, etc.).
App Type | Case No. | Country | Patent/Publication No. | |
---|---|---|---|---|
Inquire | National Phase | 2018-035 | United States | 11,866,325 |