From the perspective of catalytic reaction requirements, molecular sieves with cross pore structures, especially those with cross pore structures of 10 membered rings (mesopores) and 12 membered rings (macropores), as well as ZSM-5, ZSM-11, ZMS-12, and MCM-22 molecular sieves with cross pore structures of 10 membered rings and 10 membered rings, which have been widely used for decades, are of great significance in their synthesis and development, whether from the perspective of shape selective catalytic reaction or diffusion.
Up to now, the molecular sieves with the former channel structure mainly include natural zeolite sodium scolecite, whose structure is three-dimensional channel structure crossed by 10 membered ring and 12 membered ring; Although Nu-87 has an associated 10 membered ring and 12 membered ring pore structure, only the 10 membered ring pore is open to the outside; MCM-22 and its similar structures, SSZ-25, ERB-1, and PSH-3, although they have 10 membered ring channels and 10 membered ring channels in their structures, are separated by large cavities and molecules cannot diffuse between different channels. In addition, SS2-26, SS2-33, and CIT-1 intersect with 10 membered and 12 membered ring channels. Unfortunately, they are all composed of three types of polymorphs A, B, and C, which are defect oriented internal growth materials. In the past three years, researchers have successfully synthesized zeolite-like germanium containing molecular sieves with cross pore structures of 8-membered, 10-membered, and 12-membered rings, using 1,5-bis (methylpyrrole) pentacene as the structural guiding agent and a portion of Ge instead of Si as the raw material. This structure is the basic structural unit of [4458612] cage, and is formed into 8-membered, 10-membered, and 12-membered cross pore structures through D4R cage cylinders.
In 2003, researchers reported on the use of hexamethyldiquaternary ammonium hydroxide R (OH) 2 as a structural directing agent in 5 0Si02 : 1.0Ge02 : 0.15Al2O3； In the 1.5R (OH) 2:20H2O system, germanium containing zeolite ITQ-24 with a three-dimensional pore structure was obtained by crystallization at 150 ° C for 15 days: a 12 membered ring straight pore perpendicular to the ab plane, a 12 membered ring sinusoidal curve pore perpendicular to the a-axis direction, and a 10 membered ring pore perpendicular to it. ITQ-24 containing titanium can also be prepared using the same synthetic route. Their structural characteristics are similar to those of ITQ-22. In the ITQ-24 structure, the 12 element ring sinusoidal channel along the ab plane is surrounded by D4R cages, and this structure is similar to the structure of polytype C in SSZ-33, SSz-26, and CIT-1. In fact, based on the understanding of the structural characteristics of the polytype mentioned above, researchers have utilized the characteristics of the staggered formation of open pore structures in the presence of other macroporous structural directing agents. A zeolite like molecular sieve material with both 12 membered and 10 membered rings, as well as a D4R structure, is formed by polymerization of germanium and silicon with aluminum as the starting material.
