In
this study, the modified activated coke (AC-Tit) was prepared from
coals using titanium ore by the blending method with a one-step carbonization–activation
process. The results show that the addition of titanium ore affects
the physicochemical properties of AC-Tit. The AC-Tit samples have
higher V
mic and V
mic/V
tot ratios as well as oxygen
and CO functional group. The metal oxides (i.e., FeTiO3, TiO2, Fe2O3, and Fe) were
detected on the surface of samples, attributed to the existence of
Fe and Ti in the titanium ore. The titanium ore addition improved
the desulfurization performance of the AC-Tit effectively; the highest
sulfur capacity was 203.3 mg/g, which was much higher than that of
the blank sample (120.1 mg/g). After desulfurization, some metal sulfates,
i.e., Fe2(SO4)3 and CaSO4, were detected on the AC-Tit samples. When the sample was regenerated,
its surface area (S
BET) and V
mic did not change significantly, the relative content
of CO decreased, and COOH increased evidently. In addition,
metal sulfates on the AC-Tit samples were not decomposed during the
regeneration process. The variation of surface chemical properties
of the regenerated AC-Tit caused the reduction of the desulfurization
activity after regeneration.
The regeneration properties of a novel pyrolusite-modified activated coke (ACP) by blending method were investigated. Cyclic regeneration of ACP (ACP-Rn) shows the ACP was a good desulfurizer. The sample had the best desulfurization performance after five regeneration cycles (ACP-R5), and its sulfur capacity was 178 mg/g, 10.8% higher than that of ACP (161 mg/g). The S BET and pore volume were increased with the number of regeneration cycles, but they were not the limiting factors of the SO 2 removal. The better surface functional groups, especially the basic sites, contributed more to the improvement of desulfurization performance of ACP-Rn. The loaded metals played an important role in SO 2 removal. The accumulation of metal sulfate in ACP rapidly increased from the first to fifth regeneration cycles and then remained relatively stable during further reuse. The ACP regeneration process divided into three stages: drying, reaction, and pyrolysis. The wrapped metals relatively enhance the pyrolysis and acted as further surface modifications.
The
stumbling block to the ever-increasing need for improving air
quality remains nitrogen oxides (NO
x
).
The copper-introduced Ce/CAC-CNT (Cu
x
Ce/CAC-CNTs)
catalyst using the in situ-growth-prepared activated carbon and carbon-nanotube
composite (CAC-CNT) carrier with high sulfur dioxide tolerance was
successfully applied to low-temperature NH3–SCR
in this study. The findings indicate that the Cu
x
Ce/CAC-CNTs obtained at a 0.2 Cu/Ce molar ratio and the
calcination temperature of 450 °C showed the highest 100% NO
conversion with 95.8% N2 selectivity at 150 °C and
10 000 h–1. The incorporation of Cu improved
the Cu0.2Ce/CAC-CNTs in Lewis acid, lattice oxygen (31.99%),
and Ce3+ (26.03%). The accelerated NH3 adsorption
on acid sites, the encouraging electron transfer by the Ce4+ + Cu+ ↔ Ce3+ + Cu2+ redox
circle, and the more surface chemisorbed oxygen (Oβ) improved the catalytic activity of Cu0.2Ce/CAC-CNTs.
The NH3–SCR of Cu0.2Ce/CAC-CNTs largely
follows the L–H mechanism, together with a certain degree of
“Fast SCR.” The added Cu species effectively prevented
surface SO2 adsorption and oxidation, and the Cu0.2Ce/CAC-CNTs restored more than 94% SCR activity after 8 h of poisoning
in 50 ppm SO2 and 5 vol % H2O.
A Ce-supported activated carbon-carbon nanotube composite (Ce/AC-CNTs) catalyst was prepared by in situ formation of CNTs on AC and then modified by Ce, and was subsequently used for low-temperature selective catalytic reduction of NOx with NH3.
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