Unusual coordination state of cobalt ions in zeolites modified by aluminum chloride

Abstract

Co- and Al-modified zeolites (Al-Co-ZSM-5) were prepared by solid-state ion exchange with cobalt acetate or chloride, followed by AlCl3 immobilization from anhydrous toluene solution. Based on data from XRD, X-ray absorption (XANES/EXAFS), X-ray photoelectron spectroscopy and DRIFT spectral studies of adsorbed probe molecules (carbon monoxide, ethane), a new cobalt electronic state, bonded with surface aluminum atoms through oxygen and chlorine atoms, arises on the surface of Al-Co-ZSM-5. A new band at 2192 cm(-1) appears in the DRIFT spectrum, shifted to lower frequencies compared to CO complexes with isolated Co(2+) cations (2205 cm(-1)). Spectral data of the ethane adsorption (new strong bands in the range of 2740-2770 cm(-1)) prove the existence of specific centers of alkane activation on coordinately unsaturated cobalt cations, resulting in the interaction with aluminum chloride.

In-Depth Understanding of the Morphology Effect of α-Fe2O3 on Catalytic Ethane Destruction

“…59,60 It has been proved that the adsorption of light alkanes by metal oxides in the form of cations results in the change of relative intensity distribution of absorption bands, which largely depends on the properties of cations and metallic oxides. 60 According to the adsorption strength of ethane on all samples, it is found that Fe2O3-C is easier to adsorb water than ethane. However, compared with water, it has stronger adsorption for ethane on Fe2O3-S and Fe2O3-R.…”

Oxidation of Carbon Monoxide on Co−Ce‐Modified ZSM‐5 Zeolites: Impact of Mixed Oxo‐Species

“…In addition to the main lines, the spectra exhibit intense “shake‐up” satellites at higher binding energies, which are characteristic of Co II . To analyze the relative content of different Co species on the surface and in the volume of the zeolite, Co 2p 3/2 peaks and their satellites were decomposed into four components as described in Refs, taking into account that Co 2p 3/2 binding energies of Co II and Co III main components are 782.1±0.1 eV (peak I in Figure a) and 779.8±0.1 eV (peak II in Figure a), respectively. The contents of Co II and Co III in mono‐ and bimetallic samples are given in Table .…”

“…DRIFTS of adsorbed CO . IR spectra of chemisorbed CO are widely used to find an electronic state of metal …”

“…Promising catalysts for CO oxidation based on transition metals can be created by using zeolites as a matrix for the formation of new types of active sites . Co‐modified zeolites usually contain three main types of active Co‐sites in various proportions, depending on preparation method.…”

“…They are: (i) bare Co 2+ cations in the ion‐exchange positions of zeolites, (ii) charged metal‐ligand complexes or metal‐oxo species, and (iii) CoO and Co 3 O 4 , located at the outer surface of zeolite crystallites. The concentration, structure and location of incorporated Co species are inevitably controlled by the overall and local negative charge of the zeolite framework …”