Performance of several Keggin heteropoly acids/salts for adsorption of NOx

Aiming at controlling pollution caused by NO
_x
, several Keggin heteropoly acids/salts were evaluated concerning their activities in adsorbing NO
_x
from gas stream. All experiments were conducted in a fixed-bed reactor. The candidate heteropoly acids/salts examined comprise H
₄
PVMo
₁₁
O
₄₀
, H
₅
PV
₂
Mo
₁₀
O
₄₀
, H
₆
PV
₃
Mo
₉
O
₄₀
, (NH
₄
)
₃
PW
₁₂
O
₄₀
, (NH
₄
)
₃
PMo
₁₂
O
₄₀
, K
₃
PW
₁₂
O
₄₀
, K
₂
HPW
₁₂
O
₄₀
, KH
₂
PW
₁₂
O
₄₀
. Results showed that substitution of coordination atom Mo in the [PMo
₁₂
O
₄₀
]
^3-
anion by one or more V atoms leads to only slight change in NO
_x
adsorption activity; however, it is for the first time that nano (NH
₄
)
₃
PW
₁₂
O
₄₀
was found to have an up to 10.6% enhancement in NO
_x
adsorption efficiency in comparison with the same catalyst of normal particle size; substitution of H
⁺
in H
₃
PW
₁₂
O
₄₀
by metal cation tends to lower the adsorption activity, regardless of the metal cations introduced. By IR analysis, NO was found to be adsorbed via interaction with the proton of HPW structure.