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|Keywords: ||甲醇蒸汽重組;甲醇複合式蒸汽重組;銅觸媒;氧化鋯;氧化鈰;貴金屬;Steam reforming of methanol;oxidative steam reforming of methanol;copper catalysts;ZrO2;CeO2;noble metal|
|Issue Date: ||2014-04-02 14:53:26 (UTC+8)|
|Abstract: ||本研究宗旨在設計效能佳的SRM及OSRM產氫觸媒。本研究分三階段，第一階段為最佳觸媒成份比例探討，以商用觸媒G66B的成份比例30/60/10為起始參考，藉調變觸媒基礎成份比例，探討各成份對反應的影響，並確立其最適比例範圍。再於最適比例觸媒分別引入不同比例CeO2及ZrO2取代ZnO，有系統地探討其對觸媒於SRM及OSRM反應的真實影響及其扮演的角色，並確立其適當添加量。另於CuO/ZnO/Al2O3觸媒中分別以含浸法及共沉澱法引入少量貴金屬Pd、Pt、Ru或Rh作為促進劑，探討貴金屬對銅基觸媒於甲醇產氫反應的影響及其扮演的角色。第二階段藉由探討共沉澱pH值、熟化溫度及煅燒溫度對觸媒於SRM反應的影響，將最佳成份比例觸媒進一步最適化。第三階段以SRM反應進行觸媒穩定性測試，探討觸媒活性衰退的原因。最後以Power law及Langmuir-Hinshelwood模式進行最佳觸媒於SRM反應之動力分析。|
Power Law及Langmuir-Hinshelwood模式表達之反應速率式均能準確預測SRM反應速率，且Langmuir-Hinshelwood動力模式所反映之SRM反應機制與本研究分析論述的機制一致。; The goal of our work was to design a highly active and selective catalyst for the steam reforming of methanol (SRM) and oxidative (or combined) steam reforming of methanol (OSRM). First of all, the composition (CuO/ZnO/Al2O3 = 30/60/10) of a commercial catalyst G66B was used as a reference for investigating not only the optimal composition of CuO/ZnO/Al2O3 catalysts but also the effect of each component of the catalyst on the SRM and OSRM. The effects of CeO2 and ZrO2 over a wide range of compositions of the catalysts and their optimal composition of the catalysts were also investigated. The effect of noble metal (Pd, Pt, Ru or Rh) on the SRM and OSRM reaction over CuO/ZnO/Al2O3 catalyst were also systematically studied. The noble metal was deposited on CuO/ZnO/Al2O3 by incipient impregnation and coprecipitation methods. The roles of noble metal and CuO/ZnO/Al2O3 were clarified. Since the appropriate composition of the catalysts were determined, the catalysts were further optimized through establishing the appropriate preparation conditions such as pH value during coprecipitation, aging temperature and calcination temperature. Ultimately, the stability of these catalysts in the SRM were also observed in order to clarify the optimal catalysts. Then the kinetic modeling of SRM over the catalyst was studied.
Copper oxide and zinc oxide are the critical components of these catalysts on SRM and OSRM. Metallic copper is the active site of the CuO-based catalysts. The synergestic effect between Cu and ZnO plays an important role in SRM and OSRM reactions. Typically, Al2O3 is introduced into the binary catalyst CuO/ZnO to improve its dispersion, stability and mechanical strength. However, the interface of Cu and ZnO were decreased due to the replacement of ZnO by Al2O3 and SRM and OSRM reaction were weakened. The optimal composition of the catalysts were CuO/ZnO/Al2O3 (30/60/10) to CuO/ZnO/Al2O3(40/50/10).
Cerium oxide increased the reducibility of the catalyst, but inhibited the transformation of methoxy to formate thus weakened the SRM and OSRM reaction. Zirconium oxide improved the dispersion and reducibility of the CuO/ZnO/Al2O3 catalysts and promoted the adsorption of methanol. The promoting effect of ZrO2 was observed only on the CuO/ZnO/Al2O3 with the CuO/ZnO ratio less than 0.8. A lower CuO/ZnO ratio in the CuO/ZnO/Al2O3 catalysts was associated with greater promoting effect of ZrO2 in the SRM and OSRM reactions, which depend on appropriate interactions through the interface between CuO and ZnO.
No obvious effect of Pd and even a negative effect of Pt were observed by incipient impregnation method. With co-precipitation, noble metals were homogeneously dispersed in CuO/ZnO/Al2O3(30/60/10). They improved the reducibility of the catalysts and enhanced the dissociative adsorption of methanol. Introducing Pd, Rh or Ru promoted the conversion of methanol, but enhanced the formation of CO. Depositing Pt exhibited a high conversion of methanol and a low selectivity of CO in the SRM and OSRM reaction. The promoting effect of noble metals involved facilitating the split and adsorption of H atoms during the dehydrogenation of the intermediates in the reaction.
The formation of aurichalcite structure of the precursor of CuO/ZnO/Al2O3 (30/60/10)、1%Pt-CuO/ZnO/Al2O3(30/60/10) and CuO/ZnO/ZrO2/Al2O3(30/40/20/10) catalysts were benifited under optimal preparation conditions which the pH value of 8 during coprecipitation and the aging temperature of 80°C. The structure of aurichalcite was adventageous to the dispersion of CuO and ZnO as well the interface between them. The opitmal caicination temperature of 350°C for CuO/ZnO/Al2O3(30/60/10) and 1%Pt-CuO/ZnO/Al2O3(30/60/10) and 450°C for CuO/ZnO/ZrO2/Al2O3(30/40/20/10). The synergestic effect among Cu0, ZnO and ZrO2 was strenthen via increasing the calcination temperature of the CuO/ZnO/ZrO2/Al2O3(30/40/20/10) catalyst thus promote the catalytic activity.
The sintering of ZnO leaded to deactivation of the catalysts before a steady convertion was obtained. Since the catalytic activity reached to a steady state, the decreasing of the dispersion of ZnO could not be observed therefore the deactivation of the catalysts was caused by the coking formation on the surface of the catalysts. ZrO2 could prevent sintering and coking of the catalysts and promote the stability of the catalysts effectively. CuO/ZnO/ZrO2/Al2O3(30/40/20/10) was the optimal catalyst for SRM and OSRM reaction. The rate equation of SRM over CuO/ZnO/ZrO2/Al2O3 (30/40/20/10) obtained by Power Law and Langmuir-Hinshelwood model could predicte the reaction rate precicly and the result of kinetic study confirmed that the mechanism of SRM which was speculated and used in this study was quite reasonable.
|Appears in Collections:||[化學工程與材料工程研究所] 博碩士論文|
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