Complete Formaldehyde Removal over 3D Structured Na1.1Mn4O8@Mn5O8 Biphasic-Crystals

Graphical Formaldehyde oxidation : Complete HCHO removal was achieved at 90 °C under demanding conditions over the interconnected 3D structure of Na 1.1 Mn 4 O 8 -nanosheet@ Mn 5 O 8 -nanorod biphasic-crystals. Structure defects on the nano-rod/-sheet shared-edges significantly enhance the activity. With the increasing concerns on the formaldehyde (HCHO) hazard, the efficient oxidation of HCHO over affordable and harmless catalyst is of significant practical interest. Herein, the intermediate state of Mn 5 O 8 −Na 1.1 Mn 4 O 8 (Na−Mn 5 O 8 ) biphasic-crystal catalyst, which features Na 1.1 Mn 4 O 8 -nanosheet@ Mn 5 O 8 -nanorod interconnected 3D structure, is successfully fabricated through the anaerobic calcination of manganite followed by alkali treatment. The resultant Na−Mn 5 O 8 exhibits 100 % conversion of HCHO (150 ppm and 60000 h −1 ) and reliable stability (50 h) at 90 °C under demanding water-free feed conditions, which is superior to that of the reference samples of Mn 5 O 8 , Na 1.1 Mn 4 O 8 , MnO 2 and Na−MnO 2 . The experimental results demonstrate that the abundant structure defects (oxygen vacancies) on Na−Mn 5 O 8 , which may locate along the phase interfaces / shared-edges of Mn 5 O 8 nanorods and Na 1.1 Mn 4 O 8 nanosheets, significantly enhance the active oxygen species and finally contribute to the high activity for HCHO oxidation. Furthermore, the 3D structure of Na−Mn 5 O 8 favors mass transfer and fully exposing active sites for the HCHO adsorption and conversion. These findings reveal a way to enhance the catalytic activity of metal oxides via controlling the intermediate state of heteropical crystals.