ERS-12: A new layered tetramethylammonium silicate composed by ferrierite layers

Abstract

The new layered silicate ERS-12 was synthesized using tetraethylorthosilicate (TEOS) as source of silica and tetramethylammonium hydroxide (TMA-OH) as a structure directing agent. ERS-12 crystallizes also as germanosilicate, but not as alumino- and titanosilicate. Structure determination of as-synthesized ERS-12 was performed using α combined approach of experimental and molecular modeling techniques. It is composed by a regular stacking of ferrierite layers, with the TMA cations located in the interlayer region. Rietveld refinement of the high resolution synchrotron X-ray diffraction (SXPD) pattern of as-synthesized ERS-12 structure was firstly carried out in the monoclinic P2 1/m space group; however, to avoid the presence of linear Si–O–Si angles, final refinement was performed in the acentric P2 1 space group, which gave unit cell parameters a=10.5606(2), b=13.9692(1), c=7.4148(1) Å, β=97.981(2)° and agreement factors of R p=8.9%, R wp=12.4% and R 2 F=12.2%. Upon calcination, a remarkable change of the SXPD pattern occurred with the contemporarily presence of sharp and asymmetrically broadened reflections, indicative of the formation of a disordered structure; this was confirmed by the DIFFaX study carried out in order to evaluate the stacking sequences of ferrierite layers. The simulation suggested that the layers do not fully condense upon calcinations to form a completely connected framework.