Synthesis and physicochemical and catalytic properties of apatite-type lanthanum silicates

Abstract

Undoped and aluminum-doped lanthanum silicates with an apatite structure have been synthesized using mechanical activation, and their structure, microstructure, and catalytic properties in the oxidative coupling of methane have been investigated. The phase composition, structure, and microstructure of the silicates have been determined by X-ray diffraction, IR spectroscopy, X-ray photoelectron spectroscopy, low-temperature nitrogen adsorption, and scanning and transmission electron microscopy. The catalytic activity of silicates have been investigated in a catalytic flow reactor at 700–800°C, a CH4: O2 molar ratio of 3.8: 1 in the feed, and a residence time of 0.04 s. The catalytic properties of apatite-type lanthanum silicates can be tuned by varying the number of cationic vacancies and/or interstitial oxygen ions through isomorphic substitution of atoms with a smaller oxidation number for silicon in the apatite lattice.