Interaction Mechanism Study on Simultaneous Removal of 1,2-Dichlorobenzene and NO over MnO_x–CeO₂/TiO₂ Catalysts at Low Temperatures

Abstract

To solve the multiple air pollution problems caused during waste incineration, simultaneous control of chlorinated aromatic pollutants (e.g., chlorobenzenes, chlorophenol, and dioxins) and nitrogen oxides (NO x ) is of great significance. Titanium dioxide-supported manganese–cerium composite oxide (MnO x –CeO2/TiO2) catalysts with low-temperature activities were prepared and applied for simultaneous abatement of 1,2-dichorobenzene (o-DCBz) and NO. The interaction mechanism between o-DCBz catalytic oxidation and an NH3-SCR reaction was also studied based on the transient response experiments and several characterizations before/after the catalytic reaction. The optimum activity toward deNO x and catalytic oxidation of o-DCBz occurs both on a Mn0.15Ce0.1/Ti catalyst (i.e., Mn/Ti = 0.15, Ce/Ti = 0.1), and 97.1% of NO and 51.6% of o-DCBz are removed when the two reactions proceed independently at 150 °C. However, their simultaneous removal efficiencies are reduced mainly due to the competitive effect between o-DCBz catalytic oxidation and the NH3-SCR reaction for the limited surface acid sites and surface reactive oxygen species. In comparison, the NH3-SCR reaction is more likely to take place instead of o-DCBz catalytic oxidation, possibly because NH3 rather than o-DCBz can preferentially adsorb on the catalyst surface. In addition, the incomplete oxidation byproducts of o-DCBz residues on the catalyst surface and the chlorination of the active components of the catalyst caused by the chlorine atom from the dechlorination process of o-DCBz result in irreversible deactivation on the catalyst and lower the simultaneous abatement of o-DCBz and NO, especially at low temperatures.

Promotional Effects of FeOx on the Commercial SCR Catalyst for the Synergistic Removal of NO and Dioxins from Municipal Solid Waste Incineration Flue Gas

“…As for Figure b, the O 1s XPS spectra could be fitted to two peaks, in which the peak around 530.2 eV was attributed to lattice oxygen (denoted as O β ) and the one around 531.7 eV was ascribed to chemically adsorbed oxygen (denoted as O α ) on the catalyst surface. , The order of the O α content was 3Fe-VMT ≈ 5Fe-VMT > 7Fe-VMT > 9Fe-VMT > 1Fe-VMT > VMT, which was in accordance with the CB conversion result. Researches have revealed that the oxidative degradation of CB could be explained by the MvK mechanism: the adsorbed CB molecules were oxidized by adjacent chemisorbed oxygen on the catalyst surface, generating surface oxygen vacancies, and the consumed chemisorbed oxygen was then replenished via the dissociation adsorption of oxygen in the atmosphere on oxygen vacancies . Hence, the increase of surface chemisorbed oxygen content was the primary factor for the significant improvement of CB catalytic degradation progress, and the loading of 3 wt % FeO x strongly facilitated the CB oxidation ability of the catalyst.…”

Research advances in chlorinated benzene-containing compound oxidation catalyzed by metal oxides: activity-enhanced strategies and reaction-facilitated mechanisms

“…(2) The second view is that CBCs chemically adsorb on the surface acid site (Mn m+ ) by chlorine extraction to form phenolate intermediates at the start. 18,37,[50][51][52] The distinguished steps can be described as follows.…”

“…45 However, another view suggests that CB adsorption occurs mainly at oxygen vacancies (in combination with the MvK mechanism), which can accelerate the activation of reactive oxygen species and accelerate the oxidation rate. Oxygen vacancies are increased mainly by introducing metal oxides 50,56,87 or constructing special morphologies 37,125 to introduce defects and oxygen vacancies.…”

“…It can be concluded that the removal of strongly adsorbed Cl species at low temperatures is difficult because oxygen species may not be sufficiently active to react with Cl species but can be facilitated by hydrogen species in hydrocarbons. 50 From another point of view, CB adsorption occurs mainly at the Brønsted acid site, which can provide enough H to react with Cl at low temperatures to form HCl and promote Cl desorption, leading to its toxic inactivation. The addition of a low concentration of H 2 O induces competitive adsorption with CB and thus inhibits the catalytic activity, whereas a large amount of H 2 O addition inhibits Cl formation and promotes the removal of Cl • from the catalyst surface.…”

“…Research confirmed that the active phase of MnO x can be oxidized by reactive oxygen species to form manganese chloride. 83 Wang et al 105 prepared titanium dioxide supported manganese cerium composite oxide (MnO x –CeO 2 /TiO 2 ) demonstrated a low-temperature activity for degrading o -DCB (150 °C, 51.6%), resulting from the incomplete oxidation of o -DCB and irreversible inactivation caused by chlorine atoms.…”