Swelling of MCM-56 and MCM-22P with a new medium - surfactant-tetramethylammonium hydroxide mixtures
Swelling of MCM-56 and MCM-22P with a new medium - surfactant-tetramethylammonium hydroxide mixtures
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DOI：
10.1016/j.cattod.2012.07.040
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发表时间：
2013-04-15
期刊：
影响因子：
5.3
通讯作者：
Vitvarova, Dana
中科院分区：
文献类型：
--
作者：
Roth, Wieslaw J.;Chlubna, Pavla;Vitvarova, Dana
Two different types of layered MWW zeolite, i.e., delaminated MCM-56 and multilayer MCM-22P, have been studied for swelling using a new surfactant/tetraalkylammonium combination as the swelling reagent. The commonly used in the past tetrapropylammonium hydroxide (TPA-OH) was replaced by its tetramethylammonium (TMA-OH) homologue. The latter was previously considered unsuitable for use in swelling of MCM-22P. The extent of swelling with different amounts of TMA-OH accompanying surfactant was determined first by X-ray diffraction. Selected samples were pillared with silica and evaluated quantitatively by nitrogen sorption at 77 K and FTIR. The swelling of MCM-56, which is reported in detail for the first time, has been found to be more facile and extensive compared to the multi-layer MCM-22P, consistent with its delaminated nature. BET surface areas of pillared MCM-56 samples increase with the amount of hydroxide used for swelling and approach 700 m(2)/g. Pillared MCM-22P show similar trend but have somewhat lower BET values than pillared MCM-56. The observed successful swelling of MCM-22P is notable because the presence of small cations was previously found to be unfavorable for this process. FTIR measurements of selected samples confirmed higher Al/acid center content in pillared MCM-56 products in comparison to MCM-22 ones. Compared to unmodified MCM-22, there was an increase in most cases in the concentration of acid sites interacting with di-tert-butyl-pyridine. This confirms increased access of larger molecules to acid sites, which is the main goal of such swelling/pillaring treatments. (C) 2012 Elsevier B.V. All rights reserved.
