The process of the reaction among elemental mercury (Hg 0 ) and reactive flue gas components across the selective catalytic reduction (SCR) catalyst was studied in a laboratory-scale reactor. Prepared vanadia-based SCR catalysts were characterized and analyzed to understand the potential reaction pathways. Mercury oxidation was observed when pro-exposure of the SCR catalyst to HCl, followed by passing through Hg 0 /N 2 in the absence of gas-phase HCl. At testing conditions, Hg 0 was found to desorb from the catalyst surface by adding HCl to the gas steam, which implies that HCl adsorption onto the SCR catalyst is strong relative to the mercury. Surface analysis verified the absorption of HCl onto the SCR catalysts, and the potential reaction pathways were proposed. Indeed, the monomeric vanadyl sites on the catalyst surface were found to be responsible for the adsorption of both Hg 0 and HCl, which means they are active for mercury oxidation. Furthermore, the detailed Langmuir-Hinshelwood mechanism was proposed to explain the mercury oxidation on the SCR catalyst, where reactive Cl generated from adsorbed HCl reacts with adjacent Hg 0 .
A new,
highly active Ni-La2O3/SBA-15(C) catalyst
for CO2 methanation was prepared using a citrate complex
method, where the formed LaNiO3 with perovskite structure
was a key precursor. The physicochemical properties of the catalyst,
as-prepared and spent, and its catalytic performance were analyzed
in detail and compared with catalysts prepared through a typical wet
impregnation method. 10 wt % nickel with lanthanum in the molar ratio
of 1:1 was used to prepare the La-modified catalysts. It was found
that the La2O3 doping methods had a noticeable
effect on the structures of the catalysts and their catalytic performances.
Ni-La2O3/SBA-15(C) showed a high dispersion
of Ni with a small particle size less than 5 nm, which is one-third
of the particle size of that prepared by impregnation. Decent catalytic
performance was achieved with a CO2 conversion of 90.7%
and CH4 selectivity of 99.5% at 320 °C. Due to the
specific perovskite structure of LaNiO3, the interaction
between La and Ni was intensified, thus enhancing the synergistic
effect of La2O3 and Ni, which contributed to
the high dispersion of Ni nanoparticles as well as the good antisintering
and anticarbon deposition properties. Density functional theory calculations
also suggested that the catalyst derived from LaNiO3 favored
the adsorption and activation of CO2 and facilitated further
hydrogenation. This work provides an effective strategy to develop
highly active and stable catalysts for CO2 methanation.
With advantage of the solubility improving from NO into a higher valence state of nitrogen oxides, especially N 2 O 5 , the ozone-based low-temperature oxidation deNO x process was investigated, especially the N 2 O 5 formation mechanism. The temperature ranging from 60 to 150 °C and O 3 /NO ratios and residence time changing were investigated by a well-designed experiment. N 2 O 5 was detected by Fourier transform infrared spectroscopy (FTIR). A 24-step mechanism was also proposed, specially for describing the formation of N 2 O 5 . Results demonstrated that the formation of N 2 O 5 was greatly influenced by the temperature and residence time. N 2 O 5 could be formed at relatively low temperatures, such as 60−80 °C, within 3−5 s when O 3 / NO > 1.0. There was no N 2 O 5 detected when the temperature was higher than 130 °C as a result of the decomposition of NO 3 . The proposed mechanism could give a good prediction of the experimental results with kinetic simulation. To speed up the N 2 O 5 formation process and reduce the O 3 dosage and O 3 slip, a type of MnO x -based catalyst was developed. Results showed that the MnO x -loaded spherical alumina catalyst had obviously a positive effect on the formation of N 2 O 5 , with more than 90% NO converted into N 2 O 5 at 80 °C within 0.24 s and O 3 /NO = 1.5, with less than 15 ppm of O 3 leftover.
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