Effect of calcination temperature on structural properties and catalytic soot combustion activity of MnOx/wire-mesh monoliths

Manganese Oxides (MnOx) growing on AISI304 stainless steel wire-mesh monoliths with excellent catalytic performance and firm adhesion were synthesized via a hydrothermal route. The effect of calcination temperatures was deeply investigated. Systematic characterizations including XRD, Raman spectra, FT-IR, N-2 adsorption-desorption, SEM, HRSTEM-EDS, XPS, H-2-TPR, CO-TPR, O-2-TPD, Soot-TPR and ultrasound tests were conducted. With temperature increasing from 500 to 800 degrees C, the coating phase changes from alpha-MnO2 nanorods to MnCrO3 nanoblocks. Besides, MnCrO3 can tightly bond MnO2 with substrate as an interphase, and it also remarkably accelerates soot oxidation. The specimen calcined at 550 degrees C (MSS550) shows hierarchical pore structure with abundant accessible sites and more potassium content than MSS500 and MSS600. MSS700 presents the most surface oxygen species, high-valence metal elements and bulk potassium, thus showing the best activity. K+ would effectively activate gas O-2 forming O-2(-), O-2(2-) and improve the redox properties while Cr6+ and Fe3+ dopants would generate numerous oxygen vacancies and intensify stability. Moreover, MSS700 displays good stability and catalytic activity under repeatability test and ultrasonic treatment. The exfoliation rates of all the samples are only 0.08 +/- 0.03 wt %. This series of catalysts may satisfy the harsh conditions of active regeneration and show excellent performance for passive regeneration.