Catalytic performance of cerium iron complex oxides for partial oxidation of methane to synthesi
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Catalytic
methane Available online at、^n^n^f.sciencedirect.corn
。 ScienceDirectbcience irect 。 JOURNALOF E S
JOURNAL OFRAREEARTHS,VoL 26,No.5’Oct.2008,p.705 www.ve-journ ̄.com
performance of cerium iron complex oxides for partial oxidation of
to synthesis gas
LI Kongzhai(李孔斋),WANG Hua(王华),WEI Yonggang(魏永刚),LIU Mingchun(刘明春)
(FacultyofMaterialsandMetallurgyEngineering,KunmingUniversityofScienceandTechnology,Kunming650093,China)
Received 1 September 2007;revised 3 October 2007
Abstract:The cerium iron complex oxides oxygen carrier was prepared by the co—precipitation method.1_he reactions between methane and lattice oxygen from the complex oxides were investigated in a fixed micro.reactor system.The reduced oxygen carrier could be re—oxidized by air and its initial state could be restored.The characterizations of the oxygen carriers were studied using XRD,02.TPD,and H2-TPR.The results showed that the bulk lattice oxygen of CeO2-Fe201 was found to be suitable for the partial oxidation of methane to synthesis gas. There were two kinds of oxygen species on the oxygen carrier:the stronger oxygen species that was responsible for the complete oxidation of methane,and the weaker oxygen species(bulk lattice oxygen)that was responsible for the selective oxidation of methane to CO and H2 at a higher temperature.Then.the 1ost bulk lattice oxygen could be selectively supplemented by air re—oxidation at an appropriate reaction con— dition.CeFleO1 appeared on the oxygen carrier after 10 successive redox cycles,however,it was not bad for the selectivity of CO and H2.
Keywords:methane;cerium iron complex oxides;lattice oxygen;selective oxidation;syngas;cycles;rare earths
Catalytic partial oxidation of methane(POM)to synthesis gas is an attractive topic in the field of natural gas applica—
tion.However,this technology has not been commercialized owing to some problems,such as the rapid temperature in- crease of the catalyst and the risk of explosion owing to
premixing of CH4]O2 within the ignition and explosion lim—
its.To avoid these problems.some researchersL proposed a novel two—step process for the production of synthesis gas
from methane in the absence of gaseous oxidant.In this process,a suitable oxygen storage compound(OSC)was circulated between two reactors.In one reactor,methane
was oxidized to synthesis gas by the lattice oxygen of OSC,
and in the other,the reduced OSC was re—oxidized by air, water,or carbon dioxide.This technology enables us to ob—
tain better target production selectivity and avoid the risk of
explosion,and meanwhile,the cost can be grandly cut since there is no requirement for pure oxygen supply.The key of
this process is the preparation of an oxygen carrier,which
has high oxygen storage capacity and excellent performance
in oxidization—reduction reaction.
Complex oxide materials have been receiving tremendous attention because of their diverse application in automotive three—way converter fTWC).Cerium oxide belongs to fluo—
rite—type oxides,which has great oxygen storage capabil— ityt ̄-jJ.According to our previous researches.ceria-based
complex oxides that have lattice oxygen with high activity and selectivity ale ideal materials for the partial oxidation of methane to synthesis gas in the absence ofmolecular oxygen. In this study,the partial oxidation methane and redox
properties of CeO2・・Fe203 oxygen cartier prepared via co--
precipitation are studied.The CeOz-Fe203 complex oxides
were characterized bV XRD,O,一TPD,and H2-,IPR and some meaningfu1 results were obtained.
1 Experimental
1.1 Oxygen carrier preparation
Cerium iron complex oxide was prepared by co—-precipi--
tation.A solution of NaOH was gradually added into the mixed aqueous solution of Ce(NO 、,.6H,o and Fe
(NO3)3・9H20 with the Ce:Fe molar ratio of 1:1 with con. tinuous stirring.As the pH was increased to 7—8.a solution of 10%ammonia was gradually added to the mixture fill
pH=10.Subsequently,the precilc)itate was filtered and washed witIl distilled water.The resulting mixture was dried at 110。C for 24 h and calcined under ambient air at 800。C
for6h,andthentheCeO2-Fe203 samplewas obtained.
Foundation item:Project supported by the National Natural Science Foundation of China(50574046)and National Natural Science Foundation of Major Research Projects(90610035),Natural Science Foundation of Yunnan Province(2004E0058Q),High School Doctoral Subject Special Science and Research Foundation of Ministry of Education(20040674005) Corresponding author:WANG Hua(E-mail:wanghuaheat@hotmail.com;Te1.:+86—871—5153405、 一