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Impact of Conventional and Microwave Heating on SAPO‐5 Formation and Brønsted Acidic Properties
Author(s) -
Dang Thi Thuy Hanh,
Hoang DangLanh,
Schneider Matthias,
Hunger Michael,
Martin Andreas
Publication year - 2014
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.201400014
Subject(s) - crystallinity , silicon , crystallization , molecular sieve , materials science , microwave , hydrothermal synthesis , microwave oven , microwave heating , crystallography , hydrothermal circulation , analytical chemistry (journal) , nuclear chemistry , chemistry , chemical engineering , catalysis , organic chemistry , metallurgy , physics , quantum mechanics , engineering
Abstract The hydrothermal crystallization of SAPO‐5 molecular sieves with Si mole ratios in the range of 0.05 to 0.13 was performed by either conventional or microwave heating to compare the influence of these two techniques on the isomorphous substitution of phosphorus by silicon atoms in the aluminophosphate framework. An extensive characterization of the obtained silicoaluminophosphates by ICP‐OES, SEM, XRD, TPDA, and MAS NMR spectroscopy indicated that conventional heating (drying oven) led to a better crystallinity and a higher content of isolated framework silicon atoms than microwave heating. While microwave heating has the advantage of reducing the crystallization time and conventionally prepared SAPO‐5 materials show better incorporation of isolated silicon atoms into the AFI framework according to the substitution mechanism SM IIa. This lower SM IIa substitution of tetrahedral framework sites by isolated silicon atoms in microwave‐prepared SAPO‐5 materials is the reason for their lower density of Brønsted acidic bridging OH groups [Si(OH)Al]. In contrast, the density of defect OH groups, such as weakly acidic SiOH groups, is higher than for conventionally prepared samples.