Synthesis and Post‐Synthesis Transformation of Germanosilicate Zeolites

Abstract

Zeolites are one of the most important heterogeneous catalysts, with a high number of large‐scale industrial applications. While the synthesis of new zeolites remain rather limited, introduction of germanium has substantially increased our ability to not only direct the synthesis of zeolites but also to convert them into new materials post‐synthetically. The smaller Ge‐O‐Ge angles (vs. Si‐O‐Si) and lability of the Ge−O bonds in aqueous solutions account for this behaviour. This Minireview discusses critical aspects of germanosilicate synthesis and their post‐synthesis transformations to porous materials.

Mechanochemically assisted hydrolysis in the ADOR process

“…Over the last years, germanosilicate zeolites have been established as promising materials, due to their extra-large pore containing frameworks. 8 – 11 An even more recent development exploits the instability of the germanium–oxygen bond regarding hydrolysis in the so-called ADOR process. 12 – 14 In the ADOR process the conventionally assembled germanosilicate (generally via hydrothermal synthesis) is successively disassembled (hydrolysis by water/acid), organised, if necessary by means of a structure-directing agent (organic or inorganic), and finally reassembled by thermal treatment.…”

Reverse ADOR: reconstruction of UTL zeolite from layered IPC-1P

“…12,13 The ADOR process exploits labile Ge-rich double-four ring (D4R) units in germanosilicates, such as UTL or *CTH. 14,15 The structure of these zeolites consists of Si-rich layers connected by Ge-rich D4Rs. Upon selective hydrolysis of D4Rs, layered materials are formed, thus preserving their original structure.…”

“…Accordingly, the ADOR is a tool for the rational design of new zeolites by controlled 3D-2D-3D transformation. 14 The ADOR process was first studied on the UTL germanosilicate, which hydrolyses to layered IPC-1P. 16 Further manipulations of IPC-1P layers have resulted in a whole new family of materials (PCR, OKO, *PCS, IPC-7, IPC-9 and IPC-10; Fig.…”

ITQ‐69: A Germanium‐Containing Zeolite and its Synthesis, Structure Determination, and Adsorption Properties

“…[8][9][10] Up to now, more than fifty different germanium containing zeolitic structures have been described since the 70 s. [11,12] The larger germanium atomic radius introduces framework flexibility and high tolerance in the crystal structure to acute T-O-T bond angles. [13][14][15] Thus, very often the incorporation of germanium directs towards zeolites containing double four ring cages (D4R) owing to its preferential occupation of those sites. [8,[16][17][18][19][20][21][22][23] The presence of small cages, such as D4R, results in microporous solids of very low framework densities as predicted by Meier.…”

“…The integrity of the OSDA inside the zeolite was confirmed by elemental analysis (EA) and solid-state 13 C-NMR studies. EA reveals a C/N molar ratio very close to 5.0 in the as-prepared zeolite, which matches the theoretical value of 5 for the pure OSDA (Supporting Information, Table S3).…”