Abstract
La1−xAgxFeO3 (x = 0.05–0.25) perovskites deposited on a honeycomb-shaped monolithic metallic support were used as catalysts for the total oxidation of hydrocarbons. Monolithic catalysts were prepared by washcoating honeycomb substrates with lanthanum-stabilized γ-Al2O3, on which La1−xAgxFeO3 was deposited. Catalysts with La1−xAgxFeO3 perovskites show higher activity for methane oxidation at x ≥ 0.05 and hexane oxidation at x ≥ 0.1 than LaFeO3 catalyst. The perovskite catalysts were characterized by XRD, XPS, SEM, TEM, TPR-H2, O2-TPD and BET specific surface area measurement. Ag forms solid solutions with the La1−xAgxFeO3 perovskite lattice for x = 0.05–0.1. In La1−xAgxFeO3 perovskites (x ≥ 0.1), Ag0 particles with average crystallite sizes from 31 to 41 nm were also identified. When Ag is introduced into the LaFeO3 perovskite, both the changes occurring after some Ag is incorporated into its structure and the presence of large crystallites of metallic silver contribute to the catalysts’ activity increase.Graphical
Highlights
This paper presents the physicochemical properties and methane and hexane oxidation activity of monolithic catalysts containing 12.2–12.9% L aFeO3 perovskite in which some of the lanthanum was substituted with silver to give La1−xAgxFeO3, x = 0–0.25
The prepared catalytic materials are not a single phase because the X-ray diffraction (XRD) patterns of all samples, aside from reflections coming from the L aFeO3 perovskite structure, exhibit lines which are characteristic for La(OH)3 (2θ at 15.7°, 27.3°, 28.0°, 39.5° and 48.6°) (PDF Card No 83-2034) with a hexagonal system and P63/m space group (Fig. 1a–f)
The XRD patterns of the L a1−xAgxFeO3 perovskites with x = 0.1–0.25 exhibit peaks ascribed to metallic silver (2θ at 38.1°, 44.6° and 64.6°) (PDF Card No 06-4997) and the intensity of these peaks increases with the rise of Ag in the perovskite
Summary
Oxides with a perovskite A BO3 structure, where A is a rare earth element and B is a transition metal, have been investigated for years as materials for various uses [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36] They show very good catalytic properties and are less expensive than noble metals, and they can be used as catalysts. Oxygen vacancies are more common than cation vacancies in the perovskite’s structure [23]
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