Crystal Structure of Zeolite MCM-68:  A New Three-Dimensional Framework with Large Pores

Abstract

The crystal structure of the aluminosilicate MCM-68 was solved from synchrotron powder diffraction data by the program FOCUS. The unit cell framework contains Si100.6Al11.4O224. This material crystallizes in space group P42/mnm, where, after Rietveld refinement, a=18.286(1) A and c=20.208(2) A. A three-dimensional framework is found that contains continuous 12-ring channels and two orthogonal, intersecting, undulating 10-ring channels. Rietveld refinement of the model coordinates optimizes the framework geometry, to match the observed intensity profile by Rwp=0.1371, R(F2)=0.1411. It is not possible to determine the location of approximately 0.84 K+ cations remaining in the unit cell after the material is steamed and then dehydrated. The framework model also successfully predicts observed electron diffraction data in two projections, and the tetragonal projection can be determined independently from these data by direct methods. The calculated density of the framework structure is 1.66 g/cm3, and the T-site framework density is 16.6 T/1000 A3.

Selective Production of Light Olefins over MSE-type Zeolite Catalyst

“…2(a)) that intersects with two independent tortuous 10-ring channels as well as an 18 12-ring supercage ( Fig. 2(b)) accessible only through the 10-ring channels 5) . This framework also possesses eight distinct T-sites 1), 5) .…”

“…2(b)) accessible only through the 10-ring channels 5) . This framework also possesses eight distinct T-sites 1), 5) . Zeolites of this type in Hform are known to exhibit unique catalytic properties 6), 7) and are potentially useful as shape-selective catalysts for the alkylation of aromatics 8), 9) , disproportionation of ethylbenzene and bifunctional isomerization of nalkanes 10) as well as for the production of propylene by …”

“…A typical gel composition is 1.0SiO2 _ 0.1TEBOP 2 (I -)2 _ 0.375KOH _ 0.1Al(OH)3 _ 30H2O and the gel is kept statically at 160 for 16 d to give the desired product. This method has the disadvantages of the very narrow gel-composition window for the successful crystallization of pure MCM-68 and limited Si/ Al ratio of 9-12 5) , as well as difficulty in changing the chemical composition of the product through the direct crystallization of a pure MSE phase 4) resulting in other phases such as BEA, MTW, or MOR.…”

Catalytic Performance of Ce-modified MCM-68 Zeolite in the Dimethyl Ether-to-Olefin Reaction: Impact of High Calcination Temperature

“…15 Recently, we have reported that MCM-68 zeolite with threedimensional 12-10-10R channel system (MSE topology) 16,17 shows excellent catalytic performance in DTO reaction. 18,19 The relatively large 12R micropores make the MCM-68 highly resistant to coke formation, and its tunable acidity upon dealumination during acid treatments is convenient for realizing high selectivity to propylene.…”

Advances in the synthesis of titanosilicates: From the medium pore TS-1 zeolite to highly-accessible ordered materials

“…52 Most of the Ti atoms were properly introduced in isolated framework positions, as 53 MCM-68 is a multidimensional molecular sieve with a pore system comprised by a straight 12-ring chanel interconnected with two independent twisted 10-ring channels. 57 Since this material can only be prepared under a very narrow range of synthesis compositions, its preparation by direct methods is difficult. Then, the preparation of Ti-MCM-68 was performed by post-synthetic procedures, using an acid treatment for dealuminating the sample followed by gas-phase Ti insertion.…”