Structural transformation and chemical modifications of the unusual layered zeolite MWW form SSZ-70

0538094 - ÚFCH JH 2021 RIV NL eng J - Journal Article
Grzybek, J. - Kubů, Martin - Roth, Wieslaw Jerzy - Gil, B. - Čejka, J. - Kasneryk, Valeryia I.
Structural transformation and chemical modifications of the unusual layered zeolite MWW form SSZ-70.
Catalysis Today. Roč. 354, SI (2020), s. 133-140. ISSN 0920-5861. E-ISSN 1873-4308
R&D Projects: GA ČR GBP106/12/G015
Grant - others:GA MŠk(CZ) CZ.02.1.01/0.0/0.0/15_003/0000417
Institutional support: RVO:61388955
Keywords : molecular-sieve * 2d zeolite * mcm-22 * precursor * catalysts * titanosilicate
OECD category: Physical chemistry
Impact factor: 6.766, year: 2020
Method of publishing: Limited access

SSZ-70 is one of several layered forms of zeolite MMW obtained by direct synthesis with consecutive layers shifted by approximately ±1/3 of a unit cell in the horizontal direction (⟨110⟩), according to the recent structure solution report. Zeolite MWW is a valuable industrial alkylation catalyst and SSZ-70 itself was called by the inventors 'a successful catalytic material'. SSZ-70 shows characteristic powder X-ray diffraction pattern (XRD), containing a unique broad band with a roughly triangular shape and maximum at 8.5–9.0° 2θ (Cu Kα radiation), which can be used to distinguish SSZ-70 from the other MWW materials with different layer arrangements. This work concerns post-synthesis treatments of SSZ-70 to investigate its ability to produce more expanded structures by silylation, swelling and pillaring. Both boron- and aluminum-containing SSZ-70 were investigated. They showed the ability for interlayer expansion by swelling with cationic surfactants and were pillared with silica to produce micro/mesoporous hybrids with increased BET area. Not too surprisingly, the original unique layer stacking of SSZ-70 seems to have become more random and not distinguishable from the swollen forms of the other swellable MWW materials MCM-22 P and the monolayer MCM-56. Calcined SSZ-70 zeolites showed an unusual peak, assigned to (002) reflection, with d-spacing shorter than c-unit cell of the 3D MWW framework, which suggests collapse with formation of the so-called sub-zeolite form. Silylation resulted in different outcomes for B and Al SSZ-70 samples. The former produced interlayer expanded (IEZ) forms of B-SSZ-70 but did not show significant increase in pore volume and BET surface area. Silylation of Al-SSZ-70 did not yield the stabilized (IEZ) form but had a positive effect as it prevented the collapse to sub-zeolite upon calcination. Catalytic testing was carried out for the Al-containing SSZ-70 obtained by direct synthesis and for B-SSZ-70 activated by Al insertion. The former showed much higher concentration of Brønsted acid sites and 5 times faster conversion in a model alkylation reaction between benzyl alcohol and mesitylene. Pillared Al-SSZ-70 showed highest activity despite lower Al concentration due to silica pillars. Both silylation and pillaring had a positive effect on the activity in alkylation reaction with bulky molecules.
Permanent Link: http://hdl.handle.net/11104/0315908