(560gd) Degradation of Gas-Phase O-Xylene Via Non-Thermal Plasma over Fe Doped LaMnO3 Catalysts?the Byproducts Control

Degradation of
Gas-phase O-xylene via Non-thermal Plasma over Fe Doped LaMnO₃
Catalysts: the Byproducts Control

Voltaile organic
compounds (VOCs) are harmful to both environment and human health. Non-thermal
plasma (NTP) combined with catalysis is an atlernative thchnology for
remediating VOC contaminants, especially aromatic hydrocarbons. During
NTP-catalysis degradation process of gas-phase hydrocarbons, the harmless
products are CO₂ and H₂O, while the byproducts can be CO,
O₃, NO_x, and hydrocarbon fragments. To inhibit the
generation of by-products, Fe doped LaMnO₃ catalysts were developed.
Different concentration of Fe catalysts are synthesized by sol-gel method and
supported over Al₂O₃ as follows: LaMn_0.95Fe_0.05O₃,
LaMn_0.9Fe_0.1O₃ and LaMn_0.8Fe_0.2O₃.
(Marked as Fe0.05, Fe0.1 and Fe0.2 in Figure 1) The catalysts are fixed in the
back part of the dielectric barrier discharge (DBD) reactor. The experimental
results show that LaMn_0.9Fe_0.1O₃ is the better
choice with o-xylene degradation rate of 91.3% when specific input energy (SIE)
is 744.46 J/L, 4.2% higher than LaMn_0.95Fe_0.05O₃
and 10.1% higher than LaMn_0.8Fe_0.2O₃. When
LaMn_0.9Fe_0.1O₃ is added in NTP system, O₃
emission decreased 84.9% and N₂O decreased 66.7%, while CO₂
selectivity increased from 68.1% to 91.8% and CO_x conversion
increase from 51.6% to 80.9%. Various analytical techniques and experiments were
employed to explain the efficiency differences. The involvement of Fe results
in the lattice deformation of LaMnO₃, and further influence the
ratio of adsorbed oxygen and lattice oxygen, which mainly explain the
degradation rates difference and CO_x conversions difference. Besides,
high Mn⁴⁺ concentration of LaMn_0.9Fe_0.1O₃
contribute to the high inhibition rate of O₃. Moreover, Fe²⁺/Fe³⁺
redox couple reduce the emission of CO and enhance the CO₂
selectivity. The formation of N₂O is not only resulted from the
reaction between N₂ and O₂ directly but also attributed
to the oxygen-containing molecules. On the other hand, N₂O can be
decomposed in gas-phase or over the catalysts in plasma atmosphere. The joint
effects of formation inhibition and N₂O decomposition lead to the
less emission of N₂O. As a result, O_3, N₂O, CO
and hydrocarbon fragments are all inhibited if LaMn_xFe_1-xO₃
catalysts are adopted in the NTP system and LaMn_0.9Fe_0.1O₃
is the better choice.

Figure 1. The prevalent
reaction with degradation rate, CO_x conversion, ozone concentration
and CO₂ selectivity in NTP-catalysis system.