A Zeolitic Structure (ITQ-34) with Connected 9- and 10-Ring Channels Obtained with Phosphonium Cations as Structure Directing Agents

Abstract

Zeolites with pores of different dimensions within the same structure can present specific catalytic properties derived from the possibilities of performing molecular traffic control 1 when reactants and/or products of different molecular dimensions could react and diffuse. Some examples of zeolites with pores of different sizes within the same structure are SSZ-51, 2 MCM-68, 3 ITQ-22, 4 IM-12, 5 ITQ-15, 6 and ITQ-33. 7 Special mention requires the zeolite ITQ-13 (ITH), whose structure was solved from single crystal diffraction data, and presents a system of pores by 9 × 10 × 10 rings, with pore diameters of 4.0 Å × 4.9 Å 2 , 4.8 Å × 5.7 Å 2 , and 4.7 Å × 5.1 Å 2 , respectively. 8 Because of its peculiar pore system it presents excellent catalytic properties for producing propylene when used as a FCC additive 9 as well as for toluene disproportionation. 10 ITQ-13 zeolite was synthesized 11 with hexamethonium [hexane-1,6-bis(trimethylammonium)] as structure directing agent (SDA). We have seen that the ITH structure can have at least one hypothetical polymorph (polymorph B, now on named ITQ-34) that can also be described as a stacking of zeolitic sheets connected forming double four-rings (D4R). However, while in the case of ITQ-13 (polymorph A), these sheets extend in the bc plane and stack along the a direction with a stacking sequence AAA...; in the case of ITQ-34 the stacking sequence is ABAB..., where B corresponds to the A sheet of ITQ-13 after applying a 180°rotation around the b axis and a translation of 1 / 2 along the c axis. Then, the cell axis of both polymorphs will be closely related, the b and c axis being identical because of the common basic sheet. The a axis of ITQ-34 will be double of that in ITQ-13 because of the different stacking sequence (ABAB... vs AAA...). However, to adopt a standard setting for the space group expected for ITQ-34 (Cmcm), the cell axis of ITQ-34 will need to be defined as a (ITQ-34) ) b (ITQ-13) , b (ITQ-34) ) c (ITQ-13) , and c (ITQ-34) ) 2a (ITQ-13) (Figure 1). Also, both structures will have an identical framework density of 17.4 T atoms per 1000 Å 3 .If one simulates the structure of ITQ-34 it can be seen by simple docking that hexamethonium could, in principle, be an adequate SDA for the synthesis of this material. More specifically, when a computational approach (see Supporting Information) has been applied to calculate the short-range Van der Waals (E1) and the electrostatic (E2) interactions between the optimized zeolite-SDA system for ITQ-13 and ITQ-34 and hexamethonium, it is possible to see (Table S1 in Supporting Information) that this SDA orientates slightly better toward ITQ-13 than to ITQ-34. Then, when exploring the experimental synthesis conditions in a wide range of gel compositions using hexamethonium as SDA we found that in no case was the pure ITQ-34 obtained, but mixtures of ITQ-13 and

Zeolitic Materials with Hierarchical Porous Structures

“…A lot of effort has been devoted, for example, to the synthesis of large-pore zeolites. [19][20][21][22] However, the use of large-pore zeolite structures in industrial application is limited because of some inherent problems such as low acidity, low thermal stability and unidirectional pore systems. [ 23 ] Alternatively, the formation of 'hierarchical' structured zeolites has been developed.…”

Extra-large pore zeolite (ITQ-40) with the lowest framework density containing double four- and double three-rings

“…Previously, Davis et al considered using zinc as a framework cation to promote the formation of three-rings, and while three zincosilicates containing three-rings were subsequently synthesized, none of them contain extra-large pores (7)(8)(9). Later, we have shown by theoretical and experimental work, that Ge has a directing effect toward the formation of double four-rings (D4Rs) (10,11), and the presence of these secondary building units (SBUs) has allowed the synthesis of several large and extra-large pore zeolites (12)(13)(14)(15). Among those, Instituto de Tecnologia Química number 33 (ITQ-33) contains D4Rs and three-ring units in the structure and has a low framework density (12.3 T∕1;000 Å 3 ).…”

Structure Analysis in Zeolite Research: From Framework Topologies to Functional Properties

“…6.3 ). Modifi ed building blocks of that type were discovered in a number of framework structures solved later, e.g., ITQ-26 [ 12 ], ITQ-13 [ 13 ], and ITQ-34 [ 14 ].…”

“…These are the framework structure types containing D4R units and the corresponding type materials which have been obtained by the ITQ synthesis group where the fl uoride route was developed: ISV (ITQ-7) [ 110 ], ITW (ITQ-12) [ 12 ], ITH (ITQ-13) [ 13 ], BEC (beta polymorph C or ITQ-17) [ 36 ], IWW (ITQ-22) [ 11 ], IWR (ITQ-24) [ 11 ], IWS (ITQ-26) [ 12 ], IWV (ITQ-27) [ 111 ], ITR (ITQ-34) [ 14 ], -ITV (ITQ-37) [ 112 ], and IRR (ITQ-44) [ 113 ]. In addition, the all-silica LTA (ITQ-29) [ 114 ] was also obtained using fl uoride as one of the structure directors.…”