Abstract
This paper deals with the synthesis results obtained mostly from pure silica systems in the presence of (CH3 )3 N+ (CH2 )n N+ (CH3 )3 ions (n = 5 , 6, 9 or 10) in fluoride media, but also in the presence of (CH3 )3 N+ (CH2 )n O(CH2 )n N+ (CH3 )3 ions (n = 2 or 4) in hydroxide or fluoride media. A variety of zeolites form, namely ZSM-48, MTW-type, BEA-type, MFI-type, ITH-type zeolites, but also, in case of pronounced degradation of the template into N(CH3 )4 + or N(CH3 )3 , AST-type, MTN-type and RUT-type materials. The samples are characterized by XRD, SEM, thermal and elementary analyses, 1 H liquid NMR (after dissolution of the sample in HF aqueous solution) and solid-state NMR (19 F, 13 C, 27 Al) spectroscopy.
Highlights
The use of diquaternary alkylammonium ions with the general formula R3N+(CH2)nN+R3 as structure directing agents (SDAs) has been widely reported, leading to a variety of zeolites, depending in particular on the length of the polymethylene chain, the nature of the R alkyl group, and on the nature of the framework atoms or of the mobilizing (OH- or F-) agent [l-15].This paper deals with the synthesis of zeolites in the presence of (CH3)3N+(CH2)nN+(CH3)3 ions with n = 5, 6, 9 or 10 in fluoride media, and in the presence of (CH3)3N+(CH2)nO(CH2)nN+(CH3)3 ions with n = 2 or 4 in hydroxide or fluoride media
According to 1H liquid NMR, the organic species present in the mother liquors as well as in the as-synthesized materials correspond to various mixtures of BTMAEE2+ derivatives, such as dimethylated or even monomethylated derivatives of this cation and N(CH3)4+ or N(CH3)3 species
The obtention of pure ZSM-48 samples is only possible at 150 or 170°C under fast crystallisation conditions, i.e. in stirred systems and/or in the presence of seeds of ZSM-48 (2% versus silica weight, prepared by heating a gel of following composition 60 SiO2; 5 RBr2; 5 Na2O; 3000 H2O at 200°C for 2 days, R being the hexamethonium cation – HM2+, according to the procedure given by Giordano et al [19])
Summary
The use of diquaternary alkylammonium ions with the general formula R3N+(CH2)nN+R3 as structure directing agents (SDAs) has been widely reported, leading to a variety of zeolites, depending in particular on the length of the polymethylene chain, the nature of the R alkyl group, and on the nature of the framework atoms or of the mobilizing (OH- or F-) agent [l-15]. This paper deals with the synthesis of zeolites in the presence of (CH3)3N+(CH2)nN+(CH3) ions with n = 5, 6, 9 or 10 in fluoride media, and in the presence of (CH3)3N+(CH2)nO(CH2)nN+(CH3) ions with n = 2 or 4 in hydroxide or fluoride media The use of the latter kind of SDAs, combining the 2 quaternary ammonium and ether chemical functions, was, to our knowledge, only once reported in the literature, leading to the formation of ZSM-11 in the presence of the 2,2-diethoxy-trimethylammonium cation [16]. Precursor gels are prepared as follows: – dissolution in the required amount of water of the organic template source (halide or hydroxide) and possibly of the inorganic base (NaOH); – addition of the optional aluminium source, followed by 30 min stirring; – addition of the silica source, followed by 45 min (hydroxide media) or h (fluoride media) stirring; – addition of HF aqueous solution, followed by min stirring. Recovered solids are caracterised by powder XRD (STOE STADI-P diffractometer, with linear position-sensitive detector, Ge monochromated CuKα1 radiation), SEM (PHILIPS XL-30 microscope), TG/DSC (SETARAM LABSYS TG-DTA thermoanalyzer), solid state NMR (mainly 19F, Bruker DSX 400 spectrometer), 1H liquid NMR (after dissolution in a HF aqueous solution, Bruker Advance 400 spectrometer)
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