**2.2 Synthesis of layered zeolites by selective removal of double four rings from germanosilicates**

Germanosilicates, with novel topologies and large-pore channels, have shown their great potential in the catalytic reactions involving bulky substrates. Ge atoms favored the formation of double four ring (D4R) and double three ring (D3R) when building the zeolite frameworks together with silica atoms, due to their longer

**Figure 3.**

*Scheme description of one-pot synthesis of MIT-1 with delaminated MWW structure.*

Ge▬O bond and smaller Ge▬O▬Ge bond angle. Then, it is easy for these D4R and D3R subunits to construct large or extra-large pore channels, such as ITQ-37 (30R) [53], ITQ-43 (28R) [54], ITQ-44 (16R) [55], etc. However, the instability of Si(Ge)▬O▬Ge bonds prevents the practical applications of germanosilicates. On the bright side, the instability of germanosilicates endowed them structural modifiable properties. Taking full advantage of this, Čejka et al. have put forward an effective strategy, called the assembly-disassembly-organization-reassembly (ADOR), to transform the 3D zeolite frameworks to 2D layered zeolite by selectively removing the Ge-rich D4R subunits in UTL germanosilicate under acidic environment to give IPC-1P lamellar intermediate (**Figure 4**) [4]. The obtained lamellar zeolite was then organized and reassembled by organic amine treatment, calcination, or interlayer silylation, giving a series of novel zeolite frameworks (IPC-*n*) [56–58]. Three of these novel UTL-derived zeolites, including OKO [59], PCR [4], and \*PCS [25], have been recognized by the IZA structure committee. The alternating stable Si-rich zeolitic layer and instable Ge-rich D4R subunits and high Ge content are the key

**Figure 4.**

*Scheme description of ADOR strategy to create layered zeolite intermediates under acidic condition and novel germanosilicate derivatives.*

**Figure 5.**

*Selective hydrolysis of germanosilicates CIT-13 under alkaline medium to give layered zeolite ECNU-21P.*

**81**

**Figure 6.**

Q2

*New Trends in Layered Zeolites*

more layered zeolites.

**3. Novel modification strategies**

*DOI: http://dx.doi.org/10.5772/intechopen.86696*

ing ITH, IWR [60], IWW [61], UOV [62], and SAZ-1 [63].

**3.1 Delamination of layered zeolite under mild conditions**

of the N2 uptake in the relative pressure of 10<sup>−</sup><sup>7</sup>

*Mild delamination of MWW-layered zeolite with the assistance of F<sup>−</sup> and Cl<sup>−</sup> ions.*

signals and the sharper Q4

delaminated UCB-2 material [66].

factors for the successful structural transformation. The ADOR strategy assisted by an acidic solution has been successfully extended to other germanosilicates, includ-

Although CIT-13 germanosilicate meets all the criteria for ADOR strategy, it failed to give any lamellar zeolite. More detailed characterization indicated that the presence of Si▬O▬Si bonds vertical to the Si-rich layers may prohibit the successful selective removal of D4R subunits [64]. Wu et al. reported a mild alkaline treatment to hydrolyze both Ge▬O▬Ge(Si) and Si▬O▬Si bonds in the D4R subunits, giving a layered intermediate ECNU-21P (**Figure 5**), which was transformed to 3D ECNU-21 zeolite upon calcination [26]. In addition, the selective removal of D4R subunits from CIT-13 zeolite eliminates the intergrowth phenomena and resulted in a single crystalline zeolite framework. The alkaline medium-assisted ADOR strategy works as a good addition to the original acid system and is expected to create

The conventional delamination process includes the swelling process and a subsequent ultrasound treatment in alkaline solution with the typical pH value of ~13, which causes severe dissolution of the intralayer structures [30, 31]. Moreover, the mesoporous phase formed form dissolved silica species in swelling process, like MCM-41, may also contribute to the high surface area, which could give cheating information for the success delamination. Zones and Katz reported a delaminated MWW zeolite synthesized under mild condition, where a solution of tetrabutylammonium fluoride and chloride surfactants with a pH value of 9 was used (**Figure 6**) [65]. The fluoride ion could form a strong interaction with Si atoms, while the chloride ions would attack Al atoms in the delamination process. High solid yield of ~90% was obtained under the mild condition compared to the yield of ~75% under classical alkaline condition with the same treatment temperature and duration. The successful delamination was strongly evidenced by the loss of interlayer 10R pores, characterized by the decrease

delaminated UCB-1 material strongly indicated that the intralayer structure was well-preserved under the mild condition. However, a nonaqueous fluoride/chloride solution was needed in the delamination of the PREFER lamellar zeolite, and dimethylformamide was proved to be a suitable solvent in producing the

< *p/p0* < 10<sup>−</sup><sup>4</sup>

resonance bands in the 29Si NMR spectrum of

. The absence of

### *New Trends in Layered Zeolites DOI: http://dx.doi.org/10.5772/intechopen.86696*

*Zeolites - New Challenges*

**80**

**Figure 5.**

**Figure 4.**

*germanosilicate derivatives.*

*Selective hydrolysis of germanosilicates CIT-13 under alkaline medium to give layered zeolite ECNU-21P.*

*Scheme description of ADOR strategy to create layered zeolite intermediates under acidic condition and novel* 

Ge▬O bond and smaller Ge▬O▬Ge bond angle. Then, it is easy for these D4R and D3R subunits to construct large or extra-large pore channels, such as ITQ-37 (30R) [53], ITQ-43 (28R) [54], ITQ-44 (16R) [55], etc. However, the instability of Si(Ge)▬O▬Ge bonds prevents the practical applications of germanosilicates. On the bright side, the instability of germanosilicates endowed them structural modifiable properties. Taking full advantage of this, Čejka et al. have put forward an effective strategy, called the assembly-disassembly-organization-reassembly (ADOR), to transform the 3D zeolite frameworks to 2D layered zeolite by selectively removing the Ge-rich D4R subunits in UTL germanosilicate under acidic environment to give IPC-1P lamellar intermediate (**Figure 4**) [4]. The obtained lamellar zeolite was then organized and reassembled by organic amine treatment, calcination, or interlayer silylation, giving a series of novel zeolite frameworks (IPC-*n*) [56–58]. Three of these novel UTL-derived zeolites, including OKO [59], PCR [4], and \*PCS [25], have been recognized by the IZA structure committee. The alternating stable Si-rich zeolitic layer and instable Ge-rich D4R subunits and high Ge content are the key

factors for the successful structural transformation. The ADOR strategy assisted by an acidic solution has been successfully extended to other germanosilicates, including ITH, IWR [60], IWW [61], UOV [62], and SAZ-1 [63].

Although CIT-13 germanosilicate meets all the criteria for ADOR strategy, it failed to give any lamellar zeolite. More detailed characterization indicated that the presence of Si▬O▬Si bonds vertical to the Si-rich layers may prohibit the successful selective removal of D4R subunits [64]. Wu et al. reported a mild alkaline treatment to hydrolyze both Ge▬O▬Ge(Si) and Si▬O▬Si bonds in the D4R subunits, giving a layered intermediate ECNU-21P (**Figure 5**), which was transformed to 3D ECNU-21 zeolite upon calcination [26]. In addition, the selective removal of D4R subunits from CIT-13 zeolite eliminates the intergrowth phenomena and resulted in a single crystalline zeolite framework. The alkaline medium-assisted ADOR strategy works as a good addition to the original acid system and is expected to create more layered zeolites.
