Rare earth-doped manganese dioxide (RE-MnO₂) was developed for thermocatalytic degradation of formaldehyde. One part of cerium or samarium ions were substituted for the manganese ions in α-MnO₂, and the others existed in the form of RE oxides. The RE doping enhanced thermocatalytic activity of MnO₂. Samarium oxide did not possess thermocatalytic activity while cerium oxide facilitated the formaldehyde degradation.

Abstract

The development of high efficiency thermocatalysts remains a great challenge for gaseous formaldehyde elimination. Herein, rare earth-doped manganese dioxide (RE-MnO₂) particles with sizes of approximately 200 nm were deposited on corrugated silica carrier (CSC) by using cerium or samarium as dopants. One part of rare earth ions in RE-MnO₂/CSC were substituted for the manganese ions in α-MnO₂, and the other part existed in the form of cerium oxide or samarium oxide. RE-MnO₂/CSC exhibited better thermocatalytic activity than MnO₂/CSC. The formaldehyde removal efficiency over RE-MnO₂/CSC reached nearly 100 % even after cycle tests of 5 times. Both the cerium and samarium doping accelerated HCHO oxidation via increasing lattice oxygen and Mn⁴⁺ amounts, improving low-temperature redox properties, and reducing apparent activation energy. Notably, the RE oxides in the catalysts played different roles in HCHO degradation. Samarium oxide did not possess thermocatalytic activity, while cerium oxide in RE-MnO₂/CSC participated directly in the formaldehyde degradation via the CeO₂↔Ce₂O₃ redox reaction and facilitated the oxidation of Mn₂O₃ into MnO₂. This work revealed the effect mechanisms of RE doping and RE oxide on the enhanced thermocatalytic activity, and provided a novel viewpoint to develop RE-doped catalysts for formaldehyde removal.