Carbon Dioxide Methanation over Yttria-doped Ceria/γ-Alumina Supported Nickel Catalyst

氧化釔添加氧化鈰／氧化鋁擔載之鎳觸媒行二氧化碳甲烷化之研究

王振熙(Jenshi B. Wang) ； 陳培銘(Pei-Ming Chen) ； 黃大仁(Ta-Jen Huang)

《Journal of the Chinese Institute of Chemical Engineers》 32卷4期 (2001/07) Pp. 303-310

https://doi.org/10.6967/JCICE.200107.0303

摘要

本研究旨在利用具有氧空洞的氧化釔添加氧化鈰（YDC）行鎳觸媒擔體改質，並以共含浸法分散YDC於γ-Al2O3上。固定鎳擔載量，藉由製備不同氧化釔添加量的Ni/YDC/γ-Al2O3觸媒，研究金屬擔體相互作用力對二氧化碳甲烷化反應的影響。
研究結果顯氧化釔添加氧化鈰改質的擔體可以顯著提昇鎳觸媒行二氧化碳甲烷化反應的催化活性。其活性提昇可歸因於氧化鈰所提供之表面氧空洞與界面鎳金屬氧化，形成Ni-Ce3+界面活性中心。實驗發現觸媒活性與甲烷選擇性隨著氧化釔添加量的增加而大幅提昇，其原因可歸因於YDC之固有整體（intrinsic bulk）氧空洞之參與，因為隨著YDC中氧化釔添加量的增加，可以有更多的整體氧空洞持續參與二氧化碳之活化，因此促成活性與選擇性之提昇。不論是二氧化碳轉化率或甲烷選擇性在YDC中氧化釔添加量約為10摩爾百分比時達到最高值，而在氧化添加量高於10摩爾百分比時，會隨氧化釔的添加而明顯下降，由此推論氧化釔添加過量，會造成氧化釔的分凝，進而堵住表面氧空洞，使得觸媒活性大幅衰退。研究結果進一步顯示，隨著氧化釔的添加可使得氧化鎳物種較易在低溫還原，推測可能在觸媒表面因富含氧化釔，抑制了氧化鎳物種晶粒的成長，進而提昇其分散性。

並列摘要

A series of yttria-doped ceria (YDC)/γ-alumina supported nickel samples were prepared by co-impregnation and used as catalysts for CO2 methanation. Temperature-programmed reduction analysis was employed to characterize the catalysts. The activity and methane selectivity of these catalysts were measured and compared. It was found that the activity of the nickel catalyst in CO2 methanation could be enhanced significantly by the surface oxygen-vacancies of ceria due to the formation of interfacial Ni-Ce3+ active centers. The activity and selectivity enhancement with yttria content of the YDC-supported nickel catalyst is suggested to result from the participation of intrinsic bulk oxygen vacancies of YDC. With increasing yttria doping into ceria, increasing number of bulk oxygen vacancies can participate steadily in the activation of CO2, thereby leading to the observed enhancement of activity and selectivity. Both CO2 conversion and methane selectivity reached their respective maxima at ca. 10 mole % yttria in YDC. When yttria composition in YDC was greater than 10 mole%, the observed loss of catalytic activity was due to excess yttria, which resulted in segregation of the surface yttria species and covering of the surface oxygen vacancies. Enhanced dispersion of the nickel oxide species, which was responsible for their reduction at lower temperatures, was possibly due to the presence of the yttria-rich surface, thus impeding crystallite growth of the nickel oxide species.

並列關鍵字

Methanation ； Carbon dioxide ； Yttria-doped ceria ； Nickel catalyst