Hydrogen Utilization: Combustion - Hydrogen Generation, Storage, and Utilization - page 145

250-300°C, 250-200°C, 200-150°C, 150°C >

300°C < ,

(a) (b) (c) (d)

180 192 172 309 315 328

179 205 164 191 204 193

168 195 160 190 212 212 302 174 253 192 179 190

158 163 251 223 266 111 108 107 163 199 150

153
82.6
(1.06)

88.4
(1.13)

77.5
(0.94)

85.3
(1.03)

80.4
(0.92)

97.7
(1.04)

96.1
(1.04)

97.8
(1.12)

85.3
(0.96)

86.1
(0.95)

90.4
(0.99)

87.6
(1.47)

91.5
(1.48)

99.0
(1.42)

94.3
(1.22)

97.9
(1.27)

88.9
(1.21)

99.5
(1.78)

98.7
(1.73)

99.7
(2.04)

98.4
(1.94)

98.6
(1.87)

98.9
(1.92)

91.2
(1.26)

88.5
(2.02)

87.1
(2.05)

98.2
(1.36)

88.6
(1.32)

99.3
(1.51)

98.6
(2.23)

98.5
(2.74)

98.2
(1.29)

99.2
(1.89)

98.6
(1.87)

FIGURE 8.5 Distribution of spot temperature, combustion efficiency ( E ) and equivalent air ratio ( λ 2 )
over catalyst surface in diffusive combustion. Heat input, 1.2 kcal·cm −2 ·h −1 . Equivalent ratio of secondary
air, λ 2 = 1.8 0.2. (a) Catalyst T h , λ 2 = 1.74, E = 83.7 − 87.3%. (b) Catalyst D 5 , λ 2 = 1.62, E = 81.2%.
(c) Catalyst D 2 , λ 2 = 1.96, E = 98.0%. (d) Catalyst G 0 , λ 2 =1.94, E = 93.0%. Source : Reproduced with
permission from Haruta et al. [12].

combustion efficiency; however, it suffered from considerable nonuniform
distribution of surface temperature. It was demonstrated that a ceramic foam
coated with Co-Mn-Ag oxide was practically utilizable for catalytic appli-
ances operating on hydrogen fuel, although it required a little preheating for
initiating combustion. Premixing of air to a 40% stoichiometric amount with
hydrogen was effective in improving combustion efficiency. In a completely
premixed operation, combustion efficiency higher than 99% was obtained in
the heat input range up to 1.6 kcal·cm −2 ·h −1 . Figure 8.5 shows representative
distribution of spot tempearature, combustion efficiency ( E ), and equivalent
air ratio over catalyst surface in diffusive combustion for several different
catalysts studied. The combustion efficiency is sensitive to both temperature
of the catalyst surface and the equivalent ratio.
In a more recent study, a mesoporous ceramic coating monolithic Pt-based
catalyst (Pt/Ce 0.6 Zr 0.4 O 2 /MgAl 2 O 4 /cordierite) was prepared from inorganic
salt and alkali and used for catalytic hydrogen combustion study [13]. The
results showed that the coating had typical spinel crystallization structure
and high surface area (more than 200 m 2 ·g −1 ). The Ce-Zr oxide modification
increased the surface area and improved the oxygen storage capacity. And
the results of hydrogen catalytic combustion indicated that this monolithic
catalyst had high activity for hydrogen combustion reaction, which could
quickly start up even at 263 K. For low temperature catalytic combustion of