Applied Catalysis B: Environmental 24 (2000) 207–217
Catalytic hydrolysis of dichlorodifluoromethane (CFC-12) on
unpromoted and sulfate promoted TiO
2
–ZrO
2
mixed oxide catalysts
Suk Yin Lai
∗
, Weixiong Pan
1
, Ching Fai Ng
Department of Chemistry and Centre for Surface Research and Analysis, Hong Kong Baptist University, Kowloon Tong, Hong Kong
Received 12 May 1999; received in revised form 1 September 1999; accepted 1 September 1999
Abstract
The mixed oxide of zirconium and titanium was investigated for the catalytic hydrolysis of dichlorodifluoromethane. The
mixed oxide was further promoted by doping with sulfate ions. It was found by both powder X-ray diffraction and Raman
spectroscopy that addition of hydrogen peroxide to the methanol solution of ZrOCl
2
and TiCl
4
before gelation was induced by
ammonia addition promoted the formation of the mixed oxide phase with the anatase structure in addition to the expected phase
of columbite structure. This increased the surface area and activity of the mixed oxide. Promotion with sulfate enhanced the
acidity and activity of the catalysts. When sulfate was added by treatment with sulfuric acid, phase transformation, depending
on the concentration of the acid used, in addition to sulfate deposition on the oxide surface, occurred. The treatment with
96% sulfuric acid resulted in a catalyst with nearly entirely the anatase structure. This catalyst was found to be the most
active, capable of complete conversion of CFC-12 and 100% selectivity to carbon dioxide at 280
◦
C. Prolonged reaction of
this catalyst at 280
◦
C for 211 h resulted neither in reduction of activity nor reduction in CO
2
selectivity. The performance of
this catalyst is among the highest reported in the literature. ©2000 Elsevier Science B.V. All rights reserved.
Keywords: Freon decomposition; Dichlorodifluoromethane; Acid catalysts; Zirconia–titania mixed oxides
1. Introduction
As chlorofluorocarbons are the main culprit leading
to the destruction of the ozone layer, their use are
to be phased out and processes by which the present
stockpile can be converted into harmless substances
are required. Such need has resulted in investigations
into the catalytic destruction of chlorofluorocarbons
by hydrogenation, oxidation or hydrolysis. The G
0
∗
Corresponding author.
E-mail address: laisy@hkbu.edu.hk (S.Y. Lai).
1
Permanent address: Department of Chemistry and State Key
Laboratory of C
1
Chemical Engineering, Tsinghua University, Bei-
jing 100084, China.
of these reactions, typified by CFC-12, at 600 K, a
temperature that is close to that employed in typical
catalytic tests are:
CCl
2
F
2
(g) + 4H
2
(g) → CH
4
(g) + 2HCl(g) + 2HF(g)
G
0
=−358.6kJ
CCl
2
F
2
(g) + O
2
(g) → CO
2
(g) + Cl
2
(g) + F
2
(g)
G
0
= 18.2kJ
CCl
2
F
2
(g) + 2H
2
O(g) → CO
2
(g) + 2HCl(g)
+ 2HF(g)G
0
=−516.9kJ
Thus, of the processes, hydrolysis is thermody-
namically most favourable. Nagata et al. studied the
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