The potential of valence to core Al X-ray emission spectroscopy to determine aluminum distribution in ferrierite zeolites was investigated. The recorded emission spectra of four samples prepared with different structure directing agents exhibit slight variations in the position of the main emission peak and the intensity of its low energy shoulder. Theoretical calculations indicate that an increased intensity of the Kb x shoulder in the Al emission spectra can be linked to a predominant occupation of the T3 site by a single aluminum atom. This study thus suggests that valence to core X-ray emission spectroscopy can be applied to help determine the occupation of aluminum at crystallographic T-sites in zeolites.Zeolites are microporous crystalline aluminosilicates whose frameworks are composed of corner sharing TO 4 tetrahedra (T = either silicon or aluminum). The mutual arrangement of these subunits defines the framework structure which is characterized by periodical pores and channels. Replacing silicon atoms with aluminum atoms at the T-sites introduces a local negative charge to the framework which can be stabilized by protons or cations, which confer the catalytic activity to the zeolite. The catalytic activity is therefore directly related to the positioning of aluminum atoms within the zeolite framework.The determination of both the location of aluminum atoms at individual T-sites (aluminum sitting) and the mutual arrangement of several aluminum atoms (aluminum distribution) remains an open question in zeolite structural analysis.1 The Magic Angle
Spinning-Nuclear Magnetic Resonance (MAS-NMR) spectroscopy of 29Si represents a standard method to address the Si-Al connectivity, however, not providing information about the absolute position of aluminum and silicon atoms inside the framework.27 Al MAS NMR is sensitive to the averaged Al-O-Si angle and therefore partially yields aluminum occupation. sequences, where at least one aluminum atom is located in the second coordination shell of another aluminum atom, has been determined. Due to a large penetration depth of X-rays, X-ray-based techniques are suited for the characterization of catalysts under reaction conditions. X-ray absorption fine structure (EXAFS) analysis combined with DFT simulations showed a preference of aluminum for the T sites in the 4-ring of zeolite beta. 7 X-ray absorption near-edge structure spectroscopy (XANES) was successfully applied to monitor aluminum coordination as a function of temperature and gas composition. 8 X-ray diffraction (XRD) techniques are, in general, not suitable for distinguishing silicon and aluminum atoms because of their similar scattering power. The structural changes induced by introducing aluminum, mainly an elongation of the T-O distance by ca. 0.1 Å, can in some cases indicate the position of aluminum. 9 However, this difference is obscured by the low Al/Si proportion at that specific T-site. Using the X-ray standing waves, the location of aluminum in scolecite (NAT framework type) has been determined. 10 Alt...