Size dependence of obstruction by CO of methanol decomposition on Rhodium nanoclusters supported by Al₂O₃/NiAl(100)

Guan-Jr Liao^1*, Yu-Yao Hsia¹, Zhen-He Liao¹, Po-Wei Hsu¹, Meng-Fan Luo¹

¹Department of Physics, National Central University, Taoyuan, Taiwan

* Presenter:Guan-Jr Liao, email:liaojohnnylkz01@gmail.com

Catalyzed decomposition of methanol is widely studied as its key reaction is applied in direct-methanol fuel cells (DMFCs). Nevertheless, the efficiency of DMFCs is attenuated by CO-like reaction intermediates on the catalysts, typically supported metal nanoclusters. To improve the efficiency, understanding the mechanism how CO obstructs the reaction or poisons the catalysts is necessary. In this report, we present the study on obstructed decomposition of methanol-d4 (CD₃OD) by CO on Rh nanoclusters supported on an ordered thin film of Al₂O₃, with scanning tunneling microscopy (STM), reflection high energy electron diffraction (RHEED) and temperature programmed desorption (TPD) under ultra-high vacuum conditions. Rh nanoclusters are chosen as they exhibit size-dependent reactivity toward methanol decomposition; the obstruction effect of CO could also vary with the cluster size. We compare the produced CO and D₂ from dehydrogenated CD₃OD adsorbed on as-prepared and CO-saturated Rh clusters. The results show that for larger clusters (diameter ≧ 1.8 nm), the produced CO and D₂ from CO saturated clusters amount to 60 % of that from as-prepared Rh clusters. For smaller clusters (1.3 nm < diameter < 1.8 nm), the obstruction effect of CO is reduced by 90%; for even smaller clusters (diameter < 1.3 nm), the obstruction effect of CO in contrast increases.

Keywords: Size dependence, CO blocking, Methanol decomposition, Rhodium nanoclusters