Synthesis and Structure of COE-11, a New Borosilicate Zeolite with a Two-Dimensional Pore System of 12-Ring Channels

The new zeolite, COE-11, was synthesized at 155 & DEG;C to 168 & DEG;C by hydrothermal synthesis from a reaction mixture of SiO2/tetraethylammonium hydroxide/H3BO3/NaOH/H2O. Because tetraethylammonium is an unspecific structure directing agent, COE-11 crystallizes in all cases together with at least one impurity phase from a selection of phases: zeolite types *BEA, CHA, FER, MFI, MOR, MTW; the layered silicates magadiite and kenyaite; and searlsite and silica polymorph quartz. The crystal structure was solved from 3D electron diffraction (3D ED) data. Subsequent structure refinements of X-ray powder diffraction (PXRD) data and single crystal electron diffraction data converged to residual values of R-F = 0.039, chi(2) = 3.6 (PXRD) and R-F = 21.81% (3D ED) confirming the structure model. COE-11 crystallizes in space group C2 with unit cell dimensions of a(0) = 17.3494(11) & ANGS;, b(0) = 17.3409(11) & ANGS;, c(0) = 14.2789(4) & ANGS; and & beta; = 113.762(2) & DEG;. The structure of COE-11 is characterized by a microporous borosilicate framework with intersecting, highly elliptical 12-ring channels running parallel (110) and (1-10) and forming a two-dimensional pore system. The Rietveld refinement provided a hint that boron partly substitutes silicon on three specific T sites of the framework. The idealized chemical composition of as-made COE-11 is [(CH3CH2)(4)N](4)[B4Si62O132] per unit cell. Physico-chemical characterization using solid-state NMR spectroscopy, SEM, TG-DTA, and ATR-FTIR spectroscopy confirmed that COE-11 is a microporous borosilicate zeolite. COE-11 is structurally closely related to zeolite beta polymorph B but differs concerning the dimensionality of the pore system, which is 2D instead of 3D.