Vol.:(0123456789) 1 3
Topics in Catalysis
https://doi.org/10.1007/s11244-018-1019-x
ORIGINAL PAPER
Insights into the Reaction Mechanism of Catalytic Wet Air Oxidation
of Ammonia Over Bimetallic Ru–Cu Catalyst
Jile Fu
1
· Dewei Xiao
1
· Qingqing Yue
1
· Lili Geng
1
· Paul Oluwaseyi Fasan
1
· Nuowei Zhang
1
· Jinbao Zheng
1
·
Bing H. Chen
1
© Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
The mechanism for catalytic wet air oxidation (CWAO) of ammonia to N
2
over Ru–Cu/C catalyst is extensively studied by
altering the initial pH, reaction temperature and atmosphere. It is found that N
2
formation can be from the catalytically selec-
tive oxidation of ammonia or the disproportionation reaction between NH
4
+
and NO
2
−
. The initial oxidation of ammonia
determines the reaction mechanism, the evolution of pH and the distribution of various nitrogen species. Over-oxidation to
nitrous acid lowers the pH of the solution due to dissociation of HNO
2
to H
+
and NO
2
−
. With the decrease of pH, the con-
centration of NH
4
+
is increased and rapidly reacts with NO
2
−
to form N
2
. The relatively lower pH also makes some nitrites
be oxidized to NO
3
−
. Enhancing the reaction of selective oxidation of ammonia to N
2
increases the selectivity to N
2
while
limits the pH decrease and NO
3
−
formation, since NO
2
−
is more dominant to HNO
2
at high pH and hardly oxidized to NO
3
−
.
The reaction temperature is one key factor to determine the reaction mechanism of CWAO of ammonia.
Graphical Abstarct
Ru-Cu/C
NH
3
+O
2
NH
3
+O
2
Low temperature
120
o
C
200
o
C
High temperature
Low temperature is favorable for selecve oxidaon to N
2
while high temperature leads to over-oxidaon to nitrite.
O
2
+2* → 2O
*
NH
3
+O
*
→ NH
*
+H
2
O
NH
*
+ O
*
→ HNO
*
+*
NH
*
+ HNO
*
→ N
2
+H
2
O+2 *
HNO
*
+ O
*
→ HNO
2
*
+*
HNO
2
*
→NO
2
-
+H
+
+*
Catalyc reacon
for N
2
formaon
NO
2
-
+NH
4
+
→N
2
+H
2
0
HNO
2
+O
2
→H
+
+NO
3
-
Evolution of pH 12 8
10
Evolution of pH 12 10
Keywords Catalytic wet air oxidation · Bimetallic Ru–Cu/C catalyst · Ammonia oxidation to nitrogen · Reaction
mechanism
Extended author information available on the last page of the article