Regioselective Distribution of Zinc Hydroxyl within Straight Channels in MFI Zeolite Nanosheets for Propane Dehydrogenation

Abstract

Direct dehydrogenation of propane (PDH) is an important industrial process to produce propylene. Transitionmetal oxides encapsulated within zeolites (TM@Zeolite) are promising nonprecious and nontoxic alternatives for commercial Pt and CrOx-based PDH catalysts, and it is of great interest to further optimize the catalytic performance of TM@Zeolite. This study describes a facile dual-ligand-directed synthetic strategy that achieves the in situ introduction of Zn sites and morphology modulation of the catalysts. The optimized ZnO@MFI-P catalyst yields a propylene formation rate of 57.9 mmol propylene •g cat −1•h −1 at 580 °C with a propylene selectivity over 95%, which is superior to bulk ZnO@MFI-B, as well as the state-of-the-art Zn-based PDH catalysts. The combined theoretical and experimental efforts evidence that the MFI-P with preferential exposure of straight channels benefits the regioselective distribution of Zn species within the straight channels. This contributes to the formation of isolated [ZnOH] species and the derived [ZnH] sites, therefore facilitating propane activation toward efficient PDH performance over the ZnO

Zinc Oxide Nanoclusters Encapsulated in MFI Zeolite as a Highly Stable Adsorbent for the Ultradeep Removal of Hydrogen Sulfide

“…1023.6 eV is detected, which is assumed to be zinc oxide in its hydroxide form, Zn(OH) + . The presence of in ZSM-5 has been confirmed in previous studies by XPS along with other spectroscopic tools. , Although the pure-silica zeolite is theoretically neutral, silicliate-1 actually exhibits a certain electronegativity due to the existence of abundant defects, which thus create a microenvironment to accommodate the Zn(OH) + species. , The other peak centered at ca. 1022.6 eV, which corresponds to ZnO, started to appear in Figure e, and its relative intensity with respect to that of the peak at 1023.6 eV increased with the zinc loading (Figure f). ,− The XPS results indicate that the framework oxygen in the zeolite could exert a higher electronegativity toward zinc in the Zn(OH) + species than that between oxygen ligand and zinc in the species of ZnO nanoclusters. , This loading-dependent interaction between the zinc species and zeolite is consistent with previous studies of zinc-containing ZSM-5 zeolites.…”

“… 23 , 24 Although the pure-silica zeolite is theoretically neutral, silicliate-1 actually exhibits a certain electronegativity due to the existence of abundant defects, which thus create a microenvironment to accommodate the Zn(OH) + species. 25 , 26 The other peak centered at ca. 1022.6 eV, which corresponds to ZnO, started to appear in Figure 2 e, and its relative intensity with respect to that of the peak at 1023.6 eV increased with the zinc loading ( Figure 2 f).…”

Revealing Formaldehyde-Mediated Methanol-to-Aromatics Reactions over Zn-Modified Zeolites by Observing the Oxygenated and Polyunsaturated Intermediates

“…The band at 280 nm was attributed to a ZnO cluster with a diameter around 1 nm. The band at 250 nm was significantly pronounced for the Zn(IE)HZSM-5 sample, arising from isolated Zn sites . The band at 208 nm was ascribed to the charge transfer transition of zinc species with the lattice of O 2– .…”

“…The band at 208 nm was ascribed to the charge transfer transition of zinc species with the lattice of O 2– . H 2 -TPR profiles displayed two reduction regions (Figure d), where a reduction peak between 400–500 °C could be attributed to the dehydroxylation of ZnOH + species and the broad peak above 600 °C indicated the reduction of ZnO particles having various sizes and different interactions with the zeolite framework. , Zn­(IE)­HZSM-5 presented only one reduction peak, corresponding to ZnOH + species, which was also dominated in the Zn­(IM-0.5%)­HZSM-5 sample. The reduction peak for ZnO particles at a higher temperature became more remarkable with higher Zn loadings.…”