Rouquerol criterion and the BET equation is in accord with the geometrical surface determined by the chord length distribution method. Therefore BET surface area (S BET) is well representative of micropore surface areas of microporous materials and of total surface area of microporous/mesoporous materials. Mechanical mixtures of mesoporous MCM-41 and microporous FAU-Y powders of known surface areas were used to calculate the respective surface areas by weighted linear combination and the results were compared to the values obtained by the t-plot method. The first slope of the t-plot determined the mesopore + external surface areas (S mes+ext). The linear fit of the first slope is in general in the range 0.01 < p/p 0 < 0.17 and contains the volumes and relative pressures at which all micropores are filled (p/p 0 > 0.10). Overestimation of S mes+ext values was evident and appropriate corrections were provided. External surface areas (S ext) were obtained from the second slope of the t-plot, without noting an overestimation of S ext , thus allowing the determination of mesopore surface areas (S mes) by difference. Micropore surface areas were calculated by subtracting S mes+ext from the total surface area, S BET. As an example, this methodology was applied to the characterization a family of hierarchical microporous/mesoporous FAU-Y (FAUmes) synthesized from H-FAU-Y (H-Y, Si/Al = 15) using C18TAB as surfactant and different NaOH/Si ratio (0.05 < NaOH/Si < 0.25). By increasing the NaOH/Si ratio in synthesis of FAUmes, it was shown that as the micropore surface area decreases, the mesopore surface area increases, while the micropore + mesopore surface area remains constant. This methodology allows accurate characterization of the surface areas of microporous/mesoporous materials.

Direct evidence of the successful incorporation of atomically dispersed molybdenum (Mo) atoms into the framework of nanosized MFI zeolite is demonstrated for the first time. Homogeneous distribution of Mo with a size of 0.05 nm is observed by scanning transmission electron microscopy high-angle annular dark-field imaging (STEM-HAADF). 31P magic-angle spinning nuclear magnetic resonance (MAS NMR) and Fourier-transform infrared (FT-IR) spectroscopy, using trimethylphosphine oxide (TMPO) and deuterated acetonitrile as probe molecules, reveal a homogeneous distribution of Mo in the framework of MFI nanozeolite, and the presence of Lewis acidity. 31P MAS NMR using TMPO shows probe molecules interacting with isolated Mo atoms in the framework, and physisorbed probe molecules in the zeolite channels. Moreover, 2D 31P–31P MAS radio frequency-driven recoupling NMR indicates the presence of one type of Mo species in different crystallographic positions in the MFI framework. The substitution of framework Si by Mo significantly reduces the silanol defect content, making the resulting zeolite highly hydrophobic. In addition, the insertion of Mo into the MFI structure induces a symmetry lowering, from orthorhombic (Pnma), typical of high silica MFI, to monoclinic (P21/n), as well as an expansion of unit cell volume. The novel material opens many opportunities of catalysts design for application in mature and emerging fields.

The texture of mesoporous FAU-Y (FAUmes) prepared by surfactant-templating in basic media is a subject of debate. It is proposed that mesoporous FAU-Y consists of: (1) ordered mesoporous zeolite networks formed by a surfactant-assisted zeolite rearrangement process involving local dissolution and reconstruction of the crystalline framework, and (2) ordered mesoporous amorphous phases as Al-MCM-41, which coexist with zeolite nanodomains obtained by a dissolution-reassembly process. By the present systematic study, performed with FAU-Y (Si/Al = 15) in the presence of octadecyltrimethylammonium bromide and 0 < NaOH/Si ratio < 0.25 at 115 °C for 20 h, we demonstrate that mesoporous FAU zeolites consist, in fact, of a complex family of materials with textural features strongly impacted by the experimental conditions. Two main families have been disclosed: (1) for 0.0625 < NaOH/Si < 0.10, FAUmes are ordered mesoporous materials with zeolite walls, which coexist with zeolite nanodomains (100-200 nm) and (2) for 0.125 < NaOH/Si < 0.25, FAUmes are ordered mesoporous materials with amorphous walls as Al-MCM-41, which coexist with zeolite nanodomains (5-100 nm). The zeolite nanodomains decrease in size with the increase of NaOH/Si ratio. Increasing NaOH/Si ratio leads to an increase of mesopore volume, while the total surface area remains constant, and to a decrease of strong acidity in line with the decrease of micropore volume. The ordered mesoporous materials with zeolite walls feature the highest acidity strength. The ordered mesoporous materials with amorphous walls present additional large pores (50-200 nm), which increase in size and amount with the increase of NaOH/Si ratio. This alkaline treatment of FAU-Y represents a way to obtain ordered mesoporous materials with zeolite walls with high mesopore volume for NaOH/Si = 0.10 and a new way to synthesize mesoporous Al-MCM-41 materials containing extralarge pores (50-200 nm) ideal for optimal diffusion (NaOH/Si = 0.25).

X-ray amorphous zeolite precursors, embryonic zeolites, are prepared using tetrapropylammonium (TPA+) hydroxide as a structure directing agent. Their physicochemical properties are compared to those of a highly crystalline zeolite ZSM-5. Embryonic zeolites contain fewer acid sites, but their micropore volume and S BET area are higher than crystalline MFI-type material synthesized with TPA+. They can be introduced in the mesopores of a shaped silica-doped alumina matrix by two procedures: (i) impregnation of externally bred embryos and (ii) in situ growth of embryos to prepare composite catalysts. Their catalytic performances in the dealkylation of 1,3,5-triisopropylbenzene, a bulky molecule hardly penetrating the micropores of most zeolites, are superior to their highly crystalline ZSM-5 counterpart and the silica-doped alumina support. This is attributed to the highly accessible active sites of embryonic zeolites, located in an open microporosity leading to shorter diffusion path lengths. They offer interesting prospects to process bulky molecules in fields such as oil refining, petrochemistry, and biomass upgrading.

The current energy transition presents many technological challenges,s uch as the development of highly stable catalysts.H erein, we report an ovel "top-down"s ynthesis approach for preparation of as ingle-site Mo-containing nanosized ZSM-5 zeolite which has atomically dispersed framework-molybdenum homogenously distributed through the zeolitec rystals.T he introduction of Mo heals most of the native point defects in the zeolite structure resulting in an extremely stable material. The important features of this singlesite Mo-containing ZSM-5 zeolite are provided by an in-depth spectroscopic and microscopic analysis.T he material demonstrates superior thermal (up to 1000 8 8C), hydrothermal (steaming), and catalytic (converting methane to hydrogen and higher hydrocarbons) stability,m aintaining the atomically disperse Mo,s tructural integrity of the zeolite,a nd preventing the formation of silanols.