73
Steam Gasification and Reforming Technologies
different methods including precipitation, microemulsion, formation of amorphous
aerogels, CuZr alloys, and so on have been successfully attempted. For this catalyst,
a large surface area of the active metals needs to be maintained to avoid rapid deactivation. For this, zirconia support should be in the amorphous state under the calcination and reaction conditions. Cu/ZnO/ZrO 2 catalyst has been found to be active
at a temperature as low as 170°C, but the catalyst deactivates rapidly at temperatures above 320°C. The deactivation can, however, be reduced by the incorporation
of Al 2 O 3 that increases the temperature of crystallization of ZrO 2 , which remains
amorphous at the reaction temperature. The incorporation of alumina also increases
both the copper and the Brunauer, Emmett, and Teller (BET) surface area, thereby
increasing the catalyst activity.
Henpraserttae and Toochinda [117] examined a novel preparation technique of
Cu/Zn catalyst over Al 2 O 3 for methanol steam reforming. The study focused on
the preparation methods of active Cu/Zn-based catalysts with and without urea by
incipient wetness impregnations to lower the metal loading and the catalyst cost.
The experimental data for methanol steam reforming were obtained in a fixed-bed
reactor in the temperature range of 453–523 K to lower the energy costs. The data
showed that the activity in the hydrogen production from the catalysts with urea was
higher than that from the catalysts without urea. The impregnated catalysts can show
the activity at temperatures as low as 453 K. The Cu/Zn catalysts prepared with an
incipient wetness impregnation over Al 2 O 3 with urea can give a hydrogen yield of
about 28%. Thus, the impregnated catalysts could be alternative catalysts for hydrogen production from methanol reforming with a lower cost of the catalyst compared
with the co-precipitation method used in the commercial operation. More details on
methanol synthesis technology from various raw materials are given by Lee [118].
The partial oxidation of methanol is attractive because it is an exothermic reaction
and it follows the reaction:
1
CH 3 OH + O 2 → CO + H
∆H
0
2
2 2
298 K = − 192.2 kJ/mol
(4.59)
2
The above reaction starts at the temperature as low as 215°C. Both the reaction rate
and the selectivity for hydrogen increase very rapidly with temperature. The carbon
monoxide formation in the entire temperature range is low. The literature has shown
that production of hydrogen and carbon dioxide increases with copper content and it
reaches the maximum with 40/60 atomic percentage of copper and zinc [117–134].
Unreduced copper–zinc oxide catalysts display very low activities and produce only
carbon dioxide and water with very little hydrogen. The catalysts, however, become
eventually reduced under high-temperature reaction conditions. The apparent activation energy and the TOF are higher at lower copper content and slightly decrease
with an increase in the copper content and then achieve a constant value. These
and some other similar data show that the reaction depends on both ZnO and CuO
phases. Methanol conversion increases with oxygen partial pressure up to 0.063 atm.
A further increase in oxygen partial pressure precipitously decreases methanol conversion. The incorporation of Al 2 O 3 (up to 15% Al) to the Cu/ZnO system results
in a lower activity, implying that aluminum has an inhibiting effect on the partial
oxidation of methanol.
Steam Gasification and Reforming Technologies
different methods including precipitation, microemulsion, formation of amorphous
aerogels, CuZr alloys, and so on have been successfully attempted. For this catalyst,
a large surface area of the active metals needs to be maintained to avoid rapid deactivation. For this, zirconia support should be in the amorphous state under the calcination and reaction conditions. Cu/ZnO/ZrO 2 catalyst has been found to be active
at a temperature as low as 170°C, but the catalyst deactivates rapidly at temperatures above 320°C. The deactivation can, however, be reduced by the incorporation
of Al 2 O 3 that increases the temperature of crystallization of ZrO 2 , which remains
amorphous at the reaction temperature. The incorporation of alumina also increases
both the copper and the Brunauer, Emmett, and Teller (BET) surface area, thereby
increasing the catalyst activity.
Henpraserttae and Toochinda [117] examined a novel preparation technique of
Cu/Zn catalyst over Al 2 O 3 for methanol steam reforming. The study focused on
the preparation methods of active Cu/Zn-based catalysts with and without urea by
incipient wetness impregnations to lower the metal loading and the catalyst cost.
The experimental data for methanol steam reforming were obtained in a fixed-bed
reactor in the temperature range of 453–523 K to lower the energy costs. The data
showed that the activity in the hydrogen production from the catalysts with urea was
higher than that from the catalysts without urea. The impregnated catalysts can show
the activity at temperatures as low as 453 K. The Cu/Zn catalysts prepared with an
incipient wetness impregnation over Al 2 O 3 with urea can give a hydrogen yield of
about 28%. Thus, the impregnated catalysts could be alternative catalysts for hydrogen production from methanol reforming with a lower cost of the catalyst compared
with the co-precipitation method used in the commercial operation. More details on
methanol synthesis technology from various raw materials are given by Lee [118].
The partial oxidation of methanol is attractive because it is an exothermic reaction
and it follows the reaction:
1
CH 3 OH + O 2 → CO + H
∆H
0
2
2 2
298 K = − 192.2 kJ/mol
(4.59)
2
The above reaction starts at the temperature as low as 215°C. Both the reaction rate
and the selectivity for hydrogen increase very rapidly with temperature. The carbon
monoxide formation in the entire temperature range is low. The literature has shown
that production of hydrogen and carbon dioxide increases with copper content and it
reaches the maximum with 40/60 atomic percentage of copper and zinc [117–134].
Unreduced copper–zinc oxide catalysts display very low activities and produce only
carbon dioxide and water with very little hydrogen. The catalysts, however, become
eventually reduced under high-temperature reaction conditions. The apparent activation energy and the TOF are higher at lower copper content and slightly decrease
with an increase in the copper content and then achieve a constant value. These
and some other similar data show that the reaction depends on both ZnO and CuO
phases. Methanol conversion increases with oxygen partial pressure up to 0.063 atm.
A further increase in oxygen partial pressure precipitously decreases methanol conversion. The incorporation of Al 2 O 3 (up to 15% Al) to the Cu/ZnO system results
in a lower activity, implying that aluminum has an inhibiting effect on the partial
oxidation of methanol.