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 YMn 2 O 5 nanofibers (average diameter: ˜93 nm) including nanowire stacked with particles, and hollow tubes with or without inside nanowires. The morphologies remained even after hydrothermal aging at 800  ℃ $\text{℃}$ for 10 h with 10% H 2 O stream. X-ray photoelectron spectrum revealed Mn 4+ /Mn 3+ ratio 0.589 on the surface of YMn 2 O 5 catalyst (YMO), indicating the existence of oxygen vacancies. The highest conversion of electrospun mullite fibers at 310  ℃ $\text{℃}$ is ˜18% higher than powder-based YMO at 352 ℃ $\text{℃}$ in the presence of 5% H 2 O at WHSV = 240,000 ml g −1  h −1 . The extracted activation energy from NO-to-NO 2 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 NO 2 desorption. The catalytic activity can be attributed to the unit occupy of the e g ( d z 2 and d x 2 -y 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.