Understanding the Role of Fe Doping in Tuning the Size and Dispersion of GaN Nanocrystallites for CO₂-Assisted Oxidative Dehydrogenation of Propane

Abstract

The Fe-doped silicalite-1 zeolite as a matrix was employed to implant GaN nanocrystallites via a combined wet impregnation with in situ nitridation method. Direct spectroscopic evidences under a vacuum unraveled that the incorporation of the isolated framework Fe atoms could cause the generation of more interior silanols and especially hydrogen-bonded groups of silanol nests, where the solvated Ga3+ ions and urea in an N2 atmosphere at high temperatures were transformed into the highly dispersed GaN nanocrystallites that were embedded simultaneously in defects of the Fe-silicalite-1 matrix with the binding structure of Si–O–GaN. Moreover, the particle size distribution of GaN can be tuned from the nanoscale (14.6 ± 3.5 nm) to sub-nanoscale (2.7 ± 0.4 nm) by regulating the molar ratio of Si/Fe. Combining the results of the temperature-programmed surface reaction (TPSR) with the measurements of temperature-programmed desorption and mass spectra (TPD-MS) using the probe molecules of C3H8 and CO2, it was proposed that isolated framework Fe species were active sites for the catalytic conversion of CO2, while the nanostructured GaN was responsible for the adsorption and activation of C3H8. Catalytic results and kinetics show that the CO2-assisted oxidative dehydrogenation of propane (CO2-ODHP) over GaN/Fe-silicalite-1 proceeds by following a two-step coupling process (direct dehydrogenation of propane (DDP) + reverse water gas shift (RWGS)) and also is a structure-sensitive reaction characterized by the dependence of GaN particle size on the specific catalytic activity and apparent activation energy of converting C3H8 and CO2. Without the occurrence of GaN sintering, the slight loss of catalytic activity caused by coke deposition was confirmed by linearly correlating the normalized amount of coke with the deactivation rate.

Recent progress in the development of catalysts for propane dehydrogenation in the presence of CO2

“…Introducing Fe 3+ sites in the zeolite framework has been reported to be a reliable way to inhibit the reduction and carbonization of Fe species. Li et al 141 prepared Fe/S-1 catalysts with different Si/Fe ratios via the hydrothermal synthesis method using EDTA as an Fe complexant and studied the catalytic mechanism of Fe in the S-1 framework for CO 2 -OPDH (Fig. 11).…”

Mass-Transfer Enhancement in the CO2 Oxidative Dehydrogenation of Propane over GaN Supported on Zeolite Nanosheets with a Short b-Axis and Hierarchical Pores

“…43 All of these peaks showed lower intensities in the catalysts under vacuum conditions obtained at different temperatures compared with the support. The results indicated that upon GaN introduction, the silanol decreased, indicating that the Si−OH group was reacted with GaN to from Si−O− GaN-H species, 44 but not covered by GaN.…”

Spatial Decoupling of Redox Chemistry for Efficient and Highly Selective Amine Photoconversion to Imines

“…402 °C, Figure S40). 59 The greater affinity of CoP@ ZnIn 2 S 4 than pristine ZnIn 2 S 4 for NBI may originate from its much larger specific surface area (233 vs 141 m 2 g −1 for ZnIn 2 S 4 ) that could provide more adsorption sites. 60 Furthermore, by selecting Co in CoP@ZnIn 2 S 4 and Zn in ZnIn 2 S 4 as NBI adsorption sites, DFT calculations in Figure 5a reveal a relatively lower adsorption energy of CoP@ZnIn 2 S 4 (−0.51 eV) than ZnIn 2 S 4 (−0.98 eV).…”