Applied Catalysis B: Environmental, Vol.247, 133-141, 2019
Electrospun YMn2O5 nanofibers: A highly catalytic activity for NO oxidation
Nanofiber catalysts are potentially promising to be equipped in the lean-burned vehicle exhaust emission system considering its facile synthesis, low-cost, long durability in contrast to the traditionally complicated powder based catalyst. Here, via electrospinning method, we synthesized YMn2O5 nanofibers (average diameter (similar to)93 nm) including nanowire stacked with particles, and hollow tubes with or without inside nanowires. The morphologies remained even after hydrothermal aging at 800 degrees C for 10 h with 10% H2O stream. X-ray photoelectron spectrum revealed Mn4+/Mn3+ ratio 0.589 on the surface of YMn2O5 catalyst (YMO), indicating the existence of oxygen vacancies. The highest conversion of electrospun mullite fibers at 310 degrees C is (similar to)18% higher than powder based YMO at 352 degrees C in the presence of 5% H2O at WHSV = 240,000 ml g(-1) h(-1). The extracted activation energy from NO-to-NO2 conversion curves of YMO nanofiber (61.68 kJ/mol) is slightly lower than that of powder-based mullite (91.45 kJ/mol), consistent with calculated 68.16 kJ/mol on the fiber YMO surface (121) with a rate-limiting step of the NO2 desorption. The catalytic activity can be attributed to the unit occupy of the e(g) (d(z)(2) and d(x-y)(2 2)) orbitals of Mn-dimer atoms around fermi level based on the combination of the theoretical calculations and DRIFTS spectra analysis. Importantly, after the hash hydrothermal-aging, the highest NO oxidation conversion of powder-based mullite is less than 50%, while the fiber maintains a conversion of 62%. Moreover, the fresh YMO fiber maintained superior oxidation stability for 12 h at its maximum conversion of 66%. This work provides the possibility for mullite oxide fibers to replace powder-based precious metal catalyst coating on monolith converter.