Page 169 - Adsorbents fundamentals and applications

154 SILICA GEL, MCM, AND ACTIVATED ALUMINA

The alkalized aluminas shown above were not fully calcined, as they were
◦
heated at 120 C (Golden et al., 1997). After being fully calcined, Henry’s con-
stants obviously would have increased further.
Adsorption of NO x on γ -alumina, as well as that alkalized with alkali carbon-
ates and hydroxides, has been studied by Lee et al. (1998; 1999). It is known that
NO does not adsorb effectively on activated alumina, whereas only NO 2 adsorbs
strongly. The mechanism of adsorption of NO 2 on alumina, was studied by Nelli
and Rochelle (1996). Their study suggested that the adsorption on alumina (and
other oxide sorbents) follows the general mechanism:
H 2 O + 3NO 2 ⇒ 2HNO 3 + NO

The reaction with the sorbed water of three NO 2 results in the formation of one
NO. This mechanism was also verified by Lee et al. (1999). Lee et al. (1999)
showed that the same mechanism was also followed for adsorption of NO 2 on
alkalized aluminas and, more importantly, the alkalis significantly increased the
adsorption of NO 2 . As expected, the order of the increase followed: Cs > Rb >
K > Na > Li.

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