Perovskite-Type Oxides: II. Redox Properties of LaMn1−xCuxO3 and LaCo1−xCuxO3 and Methane Catalytic Combustion

✍ Scribed by Luciana Lisi; Giovanni Bagnasco; Paolo Ciambelli; Sergio De Rossi; Piero Porta; Gennaro Russo; Maria Turco

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 178 KB
• Volume: 146
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1999.8327

✦ Synopsis

Redox properties of high-surface-area LaM 1؊x Cu x O 3 (M ‫؍‬ Mn or Co) perovskites prepared by the citrate method were studied by H 2 TPR and O 2 TPD techniques. We have found that the reduction of Mn 4؉ occurs in all La+Mn+Cu perovskites at temperatures lower than that of Co 3؉ in La+Co+Cu samples. The presence of copper a4ects the reduction of both Mn 4؉ and Co 3؉ , increasing the temperature of reduction. Furthermore, Mn-based perovskites with a low Cu substitution (x < 0.4) release a great amount of O 2 at high temperature. Catalytic activity toward methane combustion was investigated under diluted conditions (0.4% CH 4 and 10% O 2 , N 2 as balance) in the temperature range 673+1073 K using a 5xed bed reactor with a space velocity of 40,000 N cm 3 h ؊1 g ؊1 . All samples catalyze methane oxidation in the temperature range 673+773 K, giving complete methane conversion below 1073 K and producing 100% CO 2 . No deactivation phenomena were observed. Substitution with copper decreases catalytic activity. The higher activity of Mn-based perovskites compared with that of the corresponding Co samples with the same composition was attributed to the stronger oxidative properties of LaM 1؊x Cu x O 3 . An apparent activation energy of 23 kcal mol ؊1 was evaluated on the basis of a 5rst-order kinetic equation for all samples.