以氧化鈰修飾銅觸媒進行低溫甲醇重組反應製造氫氣

Production of hydrogen from methanol reforming at low temperatures over Cu catalysts modified by ceria

鍾良佐(Liang-Chor Chung)

指導教授 ： 葉君棣

國立清華大學/理學院/化學系/博士(2008年)

摘要

The deposition precipitation method was used to prepare a supported catalyst of Cu/ZnO and noble metal catalysts of Au/ZnO, Ag/ZnO and Pt/ZnO. Their activity were tested in a fixed bed reactor with four reforming processes, i.e., decomposition of methanol (DM), steam reforming of methanol (SRM), partial oxidation of methanol (POM) and oxidative steam reforming of methanol (OSRM). Catalyst Cu/ZnO exhibited a higher DM and SRM activity than noble metal catalysts. However, the Cu/ZnO catalyst always initiated processes of POM and OSRM at higher temperatures (~ 200 oC) than noble metal (< 120 oC). The higher initiation temperature of POM required by Cu/ZnO was attributed to its high feasibility to form inactive CuOx structures in oxygen environments.
To decrease TR of methanol reforming over Cu/ZnO catalysts, ceria of different loadings (x) were by the co-deposited. Prepared Cu/CexZnO catalysts catalysts were characterized by temperature programmed oxidation (TPO) and reduction (TPR). Characterization showed that oxygen atoms chemisorbed in two different environments, i.e., on surface (Cus2O) and at perimeter (Cup2O) of dispersed copper crystallites. Prepared Cu/CexZnO catalysts were tested with a process of POM. Measured POM performance varied with CeO2 loadings on prepared catalysts. Noteworthy, prepared Cu/CeO2 catalyst can ignite POM at RT and produces a hydrogen rich gas at a low reaction temperature of TR = 120 oC. The high activity of the Cu/CeO2 catalyst was attributed to abundant Cup sites at perimeter. A mechanism is proposed to account the performance of Cu/CexZnO catalysts in POM process. In the mechanism, regeneration of active Cus sites through reduction of CusOx by decomposed CO is regarded as the rate determining step for POM.
A reaction route of OSRM over Cu/CexZnO catalysts were investigated through comparison of four tested processes, i.e., DM, SRM, POM and OSRM, at a reaction temperature of TR ~ 225 oC. The POM process exhibited a high methanol conversion (CMeOH >80%) but a poor hydrogen yield (YH2 < 2) and a high CO selectivity (SCO > 10%). However, YH2 (~ 2.4) and SCO (< 5%) in the feed of OSRM significantly were reduced. The argument of H2O in OSRM process may be attributed to a retardation of the DM route by the endothermic SRM route. The performance of OSRM (including CMeOH, YH2 and SCO) over Cu/ZnO catalyst was substantially improved by ceria. A schematic route is proposed to account variations in the OSRM performance over prepared Cu/CexZnO catalysts.

關鍵字

氫氣製造 ； 甲醇重組 ； 銅觸媒 ； 氧化鈰修飾

並列摘要

無資料

並列關鍵字

Hydrogen production ； Reforming of methanol ； Copper catalyst ； Ceria promotion

參考文獻

1-8. References

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[2] J. Larminie, A. Dicks, “Fuel cell systems explained”, John Wiley & Sons, 2002, Chapter 1.

[5] J. Zieger, Hydrogen energy progress X (1994) 1427.

[7] D. Reister, W. Strobl, Hydrogen energy progress IX (1992) 1202.