Post-synthesis incorporation of Al into germanosilicate ITH zeolites: the influence of treatment conditions on the acidic properties and catalytic behavior in tetrahydropyranylation

Abstract

Post-synthesis alumination of germanosilicate medium-pore ITH zeolite was shown to be an effective procedure for tuning its acidity. The treatment of ITH zeolites synthesized with different chemical compositions (i.e. Si/Ge = 2.5; 4.4; 5.8) with Al(NO 3 ) 3 aqueous solution led to the formation of strong 10 Brønsted and Lewis acid sites and an increasing fraction of ultramicro-and mesopores in Ge-rich ITH samples (Si/Ge = 2.5 and 4.4). The concentration of Al incorporated in the framework increases with decreasing Si/Ge ratio in the parent ITH. The increasing temperature of alumination from 80 to 175 °C (HT conditions) resulted in 1) 1.5 -2-fold increase in the concentration of Brønsted acid sites formed; and 2) in decreasing fraction of framework Al atoms detectable with base probe molecules (i.e. pyridine, 15 2,6-di-tert-butyl-pyridine), i.e. an increased concentration of the "inner" acid sites. The activity of prepared Al-substituted ITH zeolites in tetrahydropyranylation of alcohols is enhanced with increasing amount of accessible acid sites in bulky crystals (e.g. alumination at lower temperature) or with growth the total concentration of acid centres within tiny ITH crystals (e.g. alumination under HT conditions). This trend became more prominent with increasing kinetic diameter of substrate molecules under 20 investigation (methanol < 1-propanol < 1-hexanol).

Tuning of textural properties of germanosilicate zeolites ITH and IWW by acidic leaching

“…Formation of additional micro and mesopores after the treatment of ITH zeolites with Al(NO 3 ) 3 solution (pH = 2) was reported in Ref. [52] .…”

New trends in tailoring active sites in zeolite-based catalysts

“…Recent researches have been also focused on tailoring the acidity by alumination of germanosilicate zeolites characterized by unidirectional location of Ge-enriched D4R units, e.g. medium-pore ITH, 132,167,168 large-pore IWW, 169 UOV, 170 IWR 171 , and extra-large pore UTL 164 . Strategy proposed for post-synthesizing functionalization of extra-large pore UTL zeolite via isomorphous incorporation of Sn atoms (top).…”

“…zeolites. The concentration of Al incorporated in the framework grew with the rising in 1) the concentration of used Al(NO3)3 solution (0.1 -1 M), 2) the pH (0.5 -2), and 3) the temperature of the treatment (25 -175 °C) 168,171,172. Isomorphous incorporation of Sn atoms into the framework of extra-large pore UTL zeolite was achieved using degermanation-metallation of the as-synthesized germanosilicate (Figure 7) 173.…”

Layer like porous materials with hierarchical structure

“…For quantitative studies, the values of absorption coefficient of the specific bands have been used, and the available data are listed in Table 5. For 2,6-DTBPy the absorption coefficients of pyridine IR bands 281 are often used 282 . The same bulky molecules are also used, due to their basic characters, to selectively poison external acid sites during investigation of catalytic reactions.…”