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The uniformity of these particles is visually observedand demonstrates that all particles are well defined in size by the pres-ence of HTS. As the condensable silane head is hydrophilic and the alkyltails are hydrophobic, the HTS acts as a surfactant during the solvent-evaporation process for the solid–gas interface. After hydrothermaltreatment under steam-assisted crystallization (air itself being hydro-phobic) and combustive removals of organic templates, ZSM-5 whitepowders are collected. The X-ray diffraction patterns of both conven-tional ZSM-5 and hierarchically porous ZSM-5-HTS are displayed inFig. 2. It is evident that the diffraction peaks are characteristic of report-edMFI-structuredmaterials of the same type (JCPDS No. 43-0784), andno additional crystalline phase or amorphous silica is found. ZSM-5-HTSshows some broadening of the diffraction peaks and relatively weak in-tensity as compared to the conventionally prepared ZSM-5 catalyst,similar to observations also reported in nanozeolites or HPZ syntheses.This result demonstrates a decrease in the crystalline size of the primaryzeolitic particles. Besides,when the Si/Al ratio is 20, a perceivable broad-ening of peaks can also be identified. At lower Si/Al ratios, the chargedensity of an organic structure-directing-agent (SDA) does not matchsowell in the absence of inorganic cations such asNa+. Such amismatchcan lead to the formation of defective sites or a decrease of particle sizethat causes the broadening of XRD peaks.3.2. N2-physisorption isothermsN2 adsorption–desorption isotherms of ZSM-5 and ZSM-5-HTS aredisplayed in Fig. 3 and Table 1. For conventional ZSM-5, themicropores are filled at a relative pressure of 0.1, as evidenced by the uptake of N2.For conventional ZSM-5 with Si/Al ratios of 20 and 40, no obvioushysteresis loop can be discerned from the adsorption–desorption iso-therms, showing that there is no additional porosity on the convention-al ZSM-5. However, for conventional ZSM-5 with Si/Al ratios of 70 and180, a clear hysteresis loop at relative pressures between 0.1 and 0.2are observed. This artifact hysteresis loop stems from a fluid-to-crystal-line transition of liquid N2 inside MFI structured micropores, which is aunique phenomenon for MFI topology with high Si/Al ratios [45,46].A t-plot analysis of the adsorption atmicropore range gives pore vol-umes of ca. 0.10ml•g−1for both conventional and HPZ ZSM-5, evidenc-ing the presence of micropores in these catalysts. For ZSM-5-HTS-20,the isothermbelongs to a transition between type II and type IV, accord-ing to IUPAC classifications. The large slope at a relative pressurebetween 0.01 and 0.6 indicates that multilayer adsorption dominatesfor ZSM-5-HTS-20, which is pertinent to the BET model. The largeslope is consistent with the extraordinarily large BET surface area(567m2•g−1) observed for this sample than the rest. As themicroporescannot accommodatemultilayers, it is inferred that addition of HTS ex-pands the external surface areas in dry-gel conversion. At a relativepressure of 0.7 to 0.9 a small uptake of liquid nitrogen can be observed,indicating the presence of a small number of mesopores with a broadpore size distribution. When the Si/Al ratio is increased above 40,ZSM-5-HTS, on the other hand, exhibits a typical isotherm of type IV,and an obvious jump of the N2 uptake at a relative pressure of 0.6 canbe observed. The jump in both adsorption and desorption branches ata relative pressure N0.6 is caused by the capillary condensation of liquidN2 inside mesopores, showing a large number of mesopores present inthese ZSM-5-HTS materials. The possibility of a tensile-strength-effect(TSE) due to bottle-neck shaped pores can be excluded as the loopcloses at a relative pressure above 0.6, while the TSE caused the forcedclosure of isotherms which happens at ~0.45 [46]. As TSE is a result ofconfinedmesopores by smaller sized pores, the absence of TSE indicatesthat the mesopores are connected to the external surfaces. This is oneimportant feature of the MFI structure derived from our preparationmethod, and the result is also corroborated by previous129Xe NMRmeasurements [44]. The hysteresis loop can be categorized to a H3type, implying that the additional pores belong to slit-shaped ones. Toestimate the pore size distribution in ZSM-5-HTS, the BJH model isemployed from the desorption branch, which is shown in the insets ofFig. 3. Rather broad pore-size-distributions are observed for ZSM-5-HTS with a Si/Al ratio above 40. The sum of microporous and mesopo-rous volumes is estimated by subtracting themicropore volume derivedfromthe t-plot fromthe overall adsorption volume at a relative pressureof 0.99.Data shown in Table 1 also demonstrate that the surface area andpore volume are almost independent of the Si/Al ratio for sampleswith a Si/Al ratio above 40. As the BET surface area is more pertinentto the mesopores that can accommodate multi-layers of N2, a promi-nent increase in BET surface is detected for HPZ samples. These mea-surements clearly manifest that with the inclusion of HTS to the drygel system,