Thin-felt Al-fiber-structured Pd-Co-MnOx/Al2O3 catalyst with high moisture resistance for high-throughput O3 decomposition

Abstract

Thin-felt microfibrous-structured Pd-Co-MnOx/Al2O3/Al-fiber catalysts (named Pd-Co-MnOx-Al) with low Pd-loading engineered from micro- to macro-scale are developed for the high-throughput catalytic decomposition of high level gaseous ozone (O3) under humid conditions. The catalysts are obtained by highly dispersing Pd-Co-Mn active components onto the γ-Al2O3 nanosheets endogenously grown on the thin-felt microfibrous structure consisting of 10 vol% 60 μm-Al-fiber and 90 vol% voidage, using impregnation method. This approach effectively and efficiently couples the unique form factor, thin-sheet feature, and high permeability with the high activity, markedly improved stability, and enhanced moisture resistance. The most promising 0.1Pd-Co-MnOx-Al (0.1 wt% Pd, 0.36 Co/Mn molar ratio, Co2O3 + MnO2 loading of 5 wt%) catalyst remains full O3 conversion for at least 4 h at 25 °C for a feed gas containing 1500 ± 45 ppm O3 even at a high relative humidity (RH) of 70%, using a high gas hourly space velocity of 48,000 mL gcat.–1 h–1; the full O3 conversion quickly slides to a flat of ~96% during 4 h testing at 90% RH whereas it is retrievable immediately after switching the feed gas to a dry one. The remarkable improvement of activity, stability and moisture resistance by Pd-doping of Co-MnOx-Al is, in nature, due to the highly improved and stabilized low-valent-Mn related oxygen vacancies (i.e., active sites) and markedly weakened H2O adsorption on the catalyst surface, which are verified by XRD, H2-TPR, O2-TPD, H2O-TPD and XPS measurements.