**3.3 Reorganization of layer stacking by rapid dissolution-recrystallization method**

The reorganization of layer-stacking style is a useful strategy to produce partial delaminated materials, which preserved more micropores compared to full delaminated ones [34, 75]. Although the delaminated analogs can be obtained by direct hydrothermal synthesis [10, 76, 77], the posttreatment modification is easier to control. Partial detemplating by a mild acid treatment over MWWlayered zeolite produced MCM-56 with higher external surface area than conventional 3D MWW zeolite [34, 75]. In addition to this, a novel strategy of rapid dissolution-recrystallization was reported to give an intergrowth ECNU-5 zeolite with two different polymorphs of ECNU-5A and ECNU-5B (**Figure 9**) [12]. In the SDA-containing alkaline solution, the 3D all-silica MWW precursor ITQ-1 was fast dissolved to silica species in 1 h, which were then recrystallized to a lamellar material ECNU-5P with the assistant of the unique SDA of 1,3-bis(cyclohexyl) imidazolium hydroxide. The asymmetrical cyclohexyl groups in the SDA molecule were responsible for the disordered stacking style and the resultant intergrowth structure by geometry mismatching. A new pore window with the size close to 14R was found in the ECNU-5 zeolite, different from the 12R cage in the traditional 3D MWW because of the misconnection of the up-and-down pockets from neighboring layers. ECNU-5 zeolite was later proved to be analogous to SSZ-70 zeolite [11, 77].

A direct synthesized swollen MWW material ECNU-7P can be obtained by introducing the surfactant of cetyltrimethylammonium bromide (CTAB) in the above recrystallization process (**Figure 10**) [78]. The strong inorganic-organic interaction between the surfactant and structure layer, proved by 2D <sup>1</sup> H▬29Si solidstate NMR, induced the formation of the resultant alternating stacking of inorganic MWW layers and the organic CTAB layers. The calcined ECNU-7 zeolite exhibited a hierarchical pore system and larger external surface area than that of 3D MWW zeolite. Heteroatoms, like Al and Ti, can be isomorphously incorporated into the ECNU-7 zeolite, and they showed a superior catalytic activity in the cracking of 1,3,5-triisopropylbenzene and the epoxidation of propylene with bulky cumene hydroperoxide as oxidant, respectively, compared to the traditional 3D MWW zeolite [79].

#### **Figure 9.**

*Scheme description of intergrowth ECNU-5 zeolite with novel MWW layer arrangement by rapid dissolution-recrystallization method.*

**85**

*New Trends in Layered Zeolites*

**4. Conclusions**

*Direct synthesis of swollen ECNU-7P zeolite.*

**Figure 10.**

Layered zeolites, composed of zeolitic nanosheets linked by hydrogen bonds, provide modifiable precursors for the synthesis of novel zeolite derivatives with open pore system or large external surface area. The newly developed synthesis strategies, including the usage of delicately designed bifunctional amphiphilic SDAs and the top-down selective hydrolysis of 3D germanosilicates, have unexpectedly broken the limitation of conventional hydrothermal synthesis and largely expanded

the family of layered zeolites. The successful example of layered MFI zeolite synthesized by bifunctional SDA indicated the potential of design synthesis and encouraged the researchers to explore more novel-layered zeolites. The selective degradation of germanosilicates, transforming the 3D zeolite to 2D lamellar zeolite, is highly related to the orientation distribution of instable bonds in the framework. To explore other zeolite structures besides germanosilicates with such regularity is

On the other hand, several improved modification procedures have been proposed to simplify the multistep conventional processes and avoid the harsh treatment conditions. The variation of post-synthesis modifications is potential in providing more derivatives for the layered precursors, showing the infinite pos-

The authors gratefully acknowledge the financial supports from the NSFC of China (21872025, 21533002, and 21603075) and China Ministry of Science and

expected to create new layered precursors.

sibilities of the modifiable 2D layered zeolites.

**Acknowledgements**

Technology (2016YFA0202804).

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

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

*Zeolites - New Challenges*

**method**

70 zeolite [11, 77].

zeolite [79].

**3.3 Reorganization of layer stacking by rapid dissolution-recrystallization** 

The reorganization of layer-stacking style is a useful strategy to produce partial delaminated materials, which preserved more micropores compared to full delaminated ones [34, 75]. Although the delaminated analogs can be obtained by direct hydrothermal synthesis [10, 76, 77], the posttreatment modification is easier to control. Partial detemplating by a mild acid treatment over MWWlayered zeolite produced MCM-56 with higher external surface area than conventional 3D MWW zeolite [34, 75]. In addition to this, a novel strategy of rapid dissolution-recrystallization was reported to give an intergrowth ECNU-5 zeolite with two different polymorphs of ECNU-5A and ECNU-5B (**Figure 9**) [12]. In the SDA-containing alkaline solution, the 3D all-silica MWW precursor ITQ-1 was fast dissolved to silica species in 1 h, which were then recrystallized to a lamellar material ECNU-5P with the assistant of the unique SDA of 1,3-bis(cyclohexyl) imidazolium hydroxide. The asymmetrical cyclohexyl groups in the SDA molecule were responsible for the disordered stacking style and the resultant intergrowth structure by geometry mismatching. A new pore window with the size close to 14R was found in the ECNU-5 zeolite, different from the 12R cage in the traditional 3D MWW because of the misconnection of the up-and-down pockets from neighboring layers. ECNU-5 zeolite was later proved to be analogous to SSZ-

A direct synthesized swollen MWW material ECNU-7P can be obtained by introducing the surfactant of cetyltrimethylammonium bromide (CTAB) in the above recrystallization process (**Figure 10**) [78]. The strong inorganic-organic

state NMR, induced the formation of the resultant alternating stacking of inorganic MWW layers and the organic CTAB layers. The calcined ECNU-7 zeolite exhibited a hierarchical pore system and larger external surface area than that of 3D MWW zeolite. Heteroatoms, like Al and Ti, can be isomorphously incorporated into the ECNU-7 zeolite, and they showed a superior catalytic activity in the cracking of 1,3,5-triisopropylbenzene and the epoxidation of propylene with bulky cumene hydroperoxide as oxidant, respectively, compared to the traditional 3D MWW

H▬29Si solid-

interaction between the surfactant and structure layer, proved by 2D 1

*Scheme description of intergrowth ECNU-5 zeolite with novel MWW layer arrangement by rapid* 

**84**

**Figure 9.**

*dissolution-recrystallization method.*

**Figure 10.** *Direct synthesis of swollen ECNU-7P zeolite.*
