In Situ Aluminum Migration into Zeolite Framework during Methanol-To-Propylene Reaction: An Innovation To Design Superior Catalysts

Abstract

This work involves methanol-to-propylene (MTP) conversion over aluminosilicate MFI (ZSM-5), borosilicate MFI (B-ZSM-5), and all-silica MFI (Silicate-1). Both B-ZSM-5 and Silicate-1 were inactive in MTP reaction. However, extruded Silicate-1 sample prepared by extrusion with Al2O3 binder, followed by acid washing treatment, displayed a rapid increase in methanol conversion in the initial 30 h time on stream (TOS), and then retained 99% methanol conversion, higher propylene selectivity (52.2%), and higher propylene/ethylene ratio (11.3) for 400 h TOS. Silicate-1 modified with AlCl3 or Al­(NO3)3 showed similar catalytic performance as the extruded samples. Several AlCl3-modified Silicate-1 samples after various TOS values were regenerated and characterized by NH3-termperature-programmed desorption (TPD), Fourier transform infrared (FT-IR) spectroscopy, and 27Al magic angle spinning nuclear magnetic responance (MAS NMR). The results point to continuous aluminum insertion into Silicate-1 framework during reaction in situ, which rationalizes the superior catalytic performance. By analyzing catalytic performances of AlCl3-modified samples with different amounts of defect sites, we concluded that Al migration is related to the defect sites. Finally, a catalyst with a much longer lifetime of 960 h and 53.2% propylene selectivity was developed by incorporating Al migration into hierarchical samples.

Selective Formation of α-Fe(II) Sites on Fe-Zeolites through One-Pot Synthesis

“…The additional formation of α-Fe­(II) after steaming or treatment at 900 °C coincides with the conditions where aluminum is removed from the framework. This Al forms extra-framework aluminum (Al EF ), that may reinsert into the framework. ,− In MTO conditions (H 2 O/methanol at 500 °C), Al EF is incorporated in the MFI framework and migrates through the crystal . On dealuminated *BEA, Fe­(III) FW can be built in postsynthetically …”

“…52,66−69 In MTO conditions (H 2 O/methanol at 500 °C), Al EF is incorporated in the MFI framework and migrates through the crystal. 70 On dealuminated *BEA, Fe(III) FW can be built in postsynthetically. 71 We propose the first cohort of α-Fe(II) is formed in d6rs sites in which suitable Al(III) substitutions to host α-Fe(II) preexisted.…”

Increasing the Number of Aluminum Atoms in T3 Sites of a Mordenite Zeolite by Low‐Pressure SiCl4 Treatment to Catalyze Dimethyl Ether Carbonylation

“…Diffuse reflectance infrared Fourier transport (DRIFT) spectrum of parent MOR sample shows apparent signals in the O−H stretching vibration region (3800–3300 cm −1 ) (Figure 1). The band at 3732 cm −1 is assigned to the terminal silanol groups, and the broad bands at around 3500 and 3690 cm −1 are associated with silanol groups inside defects [10b, 17e] . The distribution of silanol defects was further detected with in situ DRIFT spectra after hydrogen‐deuterium (H/D) isotope exchange (Figure 1).…”

“…The change of silanol defects of parent MOR sample after LPST was studied by FTIR spectra (Figure S7a). The spectrum of the parent sample shows broad peaks from 3700 to 3200 cm −1 , which are related to silanol defects [17e] . After treatment, these broad signals disappeared in the spectra of the treated MOR samples, indicating that silanol defects, within both 8‐MR and 12‐MR channels, are healed during LPST.…”

Preparation of hierarchical H-[B]-ZSM-5 zeolites by a desilication method as a highly selective catalyst for conversion of methanol to propylene

“…In order to overcome this drawback, several procedures have been employed to reduce the limits of diffusion and improve the catalytic activity in the MTP reaction. Instances include optimizing the synthesis conditions (Jiao et al 2013), tuning the catalyst acid sites (Song et al 2017a;Li et al 2018a), reducing zeolite crystal size (Chen et al 2016b;Petushkov et al 2011), and modification with different proper metallic and non-metallic additives such as magnesium, nickel, iron, iridium, chromium, cerium, phosphorus and the like by using incorporation, impregnation, and ion-exchange procedures (Bai et al 2016;Chen et al 2015;Gorzin and Yaripour 2019;Valle et al 2005;Yarulina et al 2016;Hadi et al 2016;Yuan et al 2019;Zhang et al 2017). Among these methods, the introduction of a promoter is a high-performance route of altering the acidity in zeolites (density and strength), hence enhancing the catalytic efficiency of the H-ZSM-5 catalyst in the MTP process and stimulating higher selectivities to propylene (Bai et al 2016;Valle et al 2005).…”