Defining aluminum-zoning during synthesis of ZSM-5 zeolites

Abstract

The aluminum migration toward the surface and the delayed addition of high-aluminum-containing species contribute to the aluminum-zoning of ZSM-5 zeolites.

Interzeolite Conversion and the Role of Aluminum: Toward Generic Principles of Acid Site Genesis and Distributions in ZSM-5 and SSZ-13

“…96,97 Gallium mobility via intra-framework migration, 98 Si island forming in silicoaluminophosphates, 99 and Al mobility in multiple works on Al zoning. [100][101][102] are literature examples of framework atom mobility during hydrothermal synthesis, justifying our presumption of T-atom mobility to explain the DCC drops in this and earlier work. 24 The alleged T-atom migration phenomena does not seem to occur in Na + containing CHA zeolites ([TMAda;Na] IZC ), as no drop in DCC was observed over time.…”

On the key role of aluminium and other heteroatoms during interzeolite conversion synthesis

“…106)). Gallium mobility via intraframework migration, 153 Si island forming in silicoaluminophosphates, 154 reorganization of Zr in Si-BEA ([Zr]-BEA formation), 155 and Al mobility in multiple works on Al zoning [156][157][158] are all literature examples of internal mobility by rearrangement, inuenced by prolonged synthesis, all with practical implications for catalysis. The latter is not different in IZC synthesized zeolites.…”

The inner heterogeneity of ZSM-5 zeolite crystals

“…Such an inhomogeneous distribution of Al in zeolite crystals is not new. Indeed, Al-zoning in FAU, [32,33] TON, [34] MOR, [35] and especially for MFI type zeolites [22,[36][37][38][39] has been reported. A gradient distribution of framework Al increasing from the core to the rim is recorded often.…”

“…[14][15][16][17] The spatial heterogeneities in crystallographic orientation and chemical composition of MFI and FER zeolites were revealed as well. [18][19][20][21][22] The structural investigation using X-ray diffraction gives key insights into the size of the coherent domains, the unit cell volume, the modification of space groups, and the presence of lattice imperfections and strain of MFI and FAU zeolites. [23][24][25] Besides, time-resolved multinuclear 13 C, 23 Na, 27 Al, and 29 Si MAS NMR spectroscopy have also been applied for monitoring the mechanistic pathways of BEA and FAU zeolites.…”