This study examines the fluoride distribution in pure silica MFI zeolite synthesized in fluoride medium using various tetra-alkyl ammonium and phosphonium cations as organic structure directing agents(OSDAs).The ^(19)...This study examines the fluoride distribution in pure silica MFI zeolite synthesized in fluoride medium using various tetra-alkyl ammonium and phosphonium cations as organic structure directing agents(OSDAs).The ^(19)F NMR spectra show a resonance at∼−65 ppm,related with the presence of fluoride atoms in the t-mel cage bonded to the silicon at T9 site,and another signal at∼−80 ppm.Through DFT calculations,the∼−80 ppm 19F NMR resonance is attributed to fluoride within the t-mel cage bonded to silicon at the T12 site.Thus,the results reported here reveal that,contrary to previous reports,there is more than one position for fluoride in the zeolite structure.The location of fluoride at T12 is stabilized by using bulky OSDAs and by increasing the concentration of defects in the MFI framework.Moreover,it is shown that the OSDA used in the synthesis determines the content and distribution of siloxy–silanol defects and fluoride in pure silica MFI zeolite.These findings highlight the impact of synthesis parameters in the charge distribution in zeolites,which ultimately governs key structural properties and potential applications of zeolite materials in catalysis and adsorption processes.展开更多
基金support by the Spanish Ministry of Science and Innovation(CEX2021-001230-S and PID2022-136934OB-I00 grants funded by MCIN/AEI/10.13039/501100011033 funded by“ERDF A way of making Europe”and TED2021-130191B-C41 grant funded by the European Union NextGenerationEU/PRTR)are gratefully acknowledgedAuthors thank also the financial support by the Generalitat Valenciana(Prometeo 2021/077)+1 种基金the Advanced Materials programme and was supported by MCIN with partial funding from European Union Next Generation EU(PRTR-C17.I1)by Generalitat Valenciana(MFA/2022/012 and MFA/2022/047).
文摘This study examines the fluoride distribution in pure silica MFI zeolite synthesized in fluoride medium using various tetra-alkyl ammonium and phosphonium cations as organic structure directing agents(OSDAs).The ^(19)F NMR spectra show a resonance at∼−65 ppm,related with the presence of fluoride atoms in the t-mel cage bonded to the silicon at T9 site,and another signal at∼−80 ppm.Through DFT calculations,the∼−80 ppm 19F NMR resonance is attributed to fluoride within the t-mel cage bonded to silicon at the T12 site.Thus,the results reported here reveal that,contrary to previous reports,there is more than one position for fluoride in the zeolite structure.The location of fluoride at T12 is stabilized by using bulky OSDAs and by increasing the concentration of defects in the MFI framework.Moreover,it is shown that the OSDA used in the synthesis determines the content and distribution of siloxy–silanol defects and fluoride in pure silica MFI zeolite.These findings highlight the impact of synthesis parameters in the charge distribution in zeolites,which ultimately governs key structural properties and potential applications of zeolite materials in catalysis and adsorption processes.
