Thermal Stability of Complex Oxide Combustion Catalyst Supports

Abstract

As part of a search for more thermostable supports for combustion catalysts for gas turbine applications, a series of complex oxide materials were prepared by sol−gel synthesis and two different coprecipitation routes. The materials were chosen on the basis of literature studies; two hexaaluminates (LaAl11O18 and BaMnAl11O19 - α), a perovskite (SrZrO3), a spinel (MgAl2O4), and a pyrochlore (La2Zr2O7). After synthesis, the materials were aged for 16 h in a flow of humid air at temperatures between 1100 and 1400 °C, simulating the actual conditions in a catalytic combustor. The aged samples were characterized by X-ray diffraction, nitrogen adsorption for determination of BET surface area, and scanning electron microscopy. The sol−gel materials generally exhibited higher thermal stability than their coprecipitated counterparts. One exception was LaAl11O18, which had the highest surface area of all materials, 8 m2/g, after aging at 1400 °C, both for the sol−gel synthesized and one coprecipitated material. The reaction paths for the high-temperature solid-state reactions depended on preparation procedure and stoichiometry of the product.

Syntesis of lanthanum zirconate hydrosols by the ion exchange method

“…This confirms strong effect of the textured substrate on process of formation of the La 2 Zr 2 O 7 epitaxial film. The La 2 Zr 2 O 7 formation processes in the sol synthesis by the ion exchange method developed in the present work and those in the coprecipitation method [11,12] are close. In both cases crystallization of lanthanum zirconate occurs during the heat treatment at temperatures above 600 °C (the structure of fluorite) and ≥1000°C (the structure of pyrochlore).…”

Clear microstructure–performance relationships in Mn-containing perovskite and hexaaluminate compounds prepared by activated reactive synthesis

“…Theory and data treatment can be found elsewhere 20,21 and are shortly summarized herein. The exchange reaction can be written as in eqn (1): 18…”

“…The sample is then treated under dynamic vacuum for 30 min. Thereafter, 56 mbar of pure 18 O 2 is introduced into the system. The masses 32, 34, and 36 m/z were monitored as a function of time to follow the exchange.…”

“…Only a few studies have been dedicated to the comparison of hexaaluminate and perovskite, from textural and morphological points of view, to highlight the thermal stability of hexaaluminates compared to perovskite materials. 17,18 When the catalytic activity per unit surface is presented, perovskites present generally higher catalytic activities. 14,19 However, at high temperatures, hexaaluminates exhibit higher catalytic activity than perovskites for oxidation reactions.…”

A comparison between hexaaluminates and perovskites for catalytic combustion applications

“…As mentioned before only few comparisons have been made between the two materials. Zwinkels compare the surface areas of several different complex metal oxides, including both hexaaluminates and perovskites and concluded that the hexaaluminates retained far larger surface areas at high temperatures than its perovskite counterparts [14].…”