Methane deep oxidation thermally stable multicomponent manganese catalyst modified with oxides of rare and alkaline-earth elements

Abstract

A thermally stable (to 1200°C) manganese oxide catalyst for the deep CH4 oxidation into CO2 by air was developed. In the course of works, new approaches to the synthesis of transitional element Mn-based polyoxide catalysts, modified with rare-earth elements (REE) La, Ce, and alkaline-earth elements (AEE) Ba, Sr by depositing them from nitrate solutions onto 2% Ce/θ-Al2O3 granules were used. It was shown that the 7% Mn-REE-AEE/2% Ce/θ-Al2O3 catalyst provided the CH4 conversion into CO2 at a level of 88–92% at 700°C and the hourly space velocity of 105 h−1. The degree of CH4 oxidation into CO2 was almost independent of the O2 and CH4 concentrations, if they were varied within the intervals 2–20 and 0.5–4.0%, respectively. To establish the reasons for the thermal stability of catalysts, complex investigations were conducted by the BET, XPA, EM, TPD, TPR, ESDR, and TPO methods. It was revealed that, under high-temperature heating to 200°C, Mn2O3 and perofskites interacted with θ-Al2O3 to form hexaluminates MnLaAl11O19, whose concentration increased, when the catalyst was promoted with Pt and Pd, and the main reason for the conservation of 7% Mn-REE-AEE/2% Ce/θ-Al2O3 catalyst activity under heating to 1200°C was the formation of thermally stable manganese hexaluminates for the deep oxidation of CH4.