Zeolites with encapsulated transition metal species are extensively applied in the chemical industry as heterogenous catalysts for favorable kinetic pathways. To elucidate the energetic insights into formation of subnano-sized molybdenum trioxide (MoO3) encapsulated/confined in zeolite Y (FAU) from constituent oxides, we performed a systematic experimental thermodynamic study using high temperature oxide melt solution calorimetry as the major tool. Specifically, the formation enthalpy of each MoO3/FAU is less endothermic than corresponding zeolite Y, suggesting enhanced thermodynamic stability. As Si/Al ratio increases, the enthalpies of formation of MoO3/FAU with identical loading (5 Mo-wt%) tend to be less endothermic, ranging from 61.1 ± 1.8 (Si/Al = 2.9) to 32.8 ± 1.4 kJ/mol TO2 (Si/Al = 45.6). Coupled with spectroscopic, structural and morphological characterizations, we revealed intricate energetics of MoO3 – zeolite Y guest – host interactions likely determined by the subtle redox and/or phase evolutions of encapsulated MoO3.

Binderless zeolite X pellets were “one-pot” synthesized via in situ hydrothermal conversion of silica gel precursors in sodium aluminate solution. The conversion and crystallization kinetics were investigated as a function of synthesis time with a spectrum of techniques. It is found that four-membered (4R) and six-membered rings (6R) are formed by linking diffused Al species with dissolved Si species during the aging period, while the zeolite X frameworks are constructed via reorganization of β cages with double six-membered rings (D6R) in crystallization process. Furthermore, GCMC simulation was conducted to elucidate 1-hexene adsorption in zeolite X as ion species and exchange degree vary, in which adsorption capacity and guest – host interaction energy were evaluated. Incorporation of Mg2+ and Ca2+ enables higher adsorption capacity, while introduction of Co2+, Ni2+, Cu2+ and Zn2+ boosts adsorption and enhances interaction energy.