Morphology-dependent CeO2 catalysis in acetylene semihydrogenation reaction.

• Morphology-dependent CeO 2 catalysis is established in C 2 H 2 semihydrogenation reaction. • Catalytic performance follows an order of r-CeO 2 -500 ≫ c-CeO 2 > r-CeO 2 -700. • Ability to chemisorb C 2 H 2 (a) follows an order of r-CeO 2 -500 ≫ c-CeO 2 ≈ r-CeO 2 -700. • Ability to dissociate H 2 follows an order of c-CeO 2 > r-CeO 2 -500 ≫ r-CeO 2 -700. We herein investigated the catalytic performances and reaction mechanisms of CeO 2 cubes (denoted as c-CeO 2), CeO 2 rods calcined at 500 °C (denoted as r-CeO 2 -500), and CeO 2 rods calcined at 700 °C (denoted as r-CeO 2 -700) in the acetylene semihydrogenation reaction. r-CeO 2 -500 is most catalytically active while r-CeO 2 -700 is least. The acetylene semihydrogenation reaction catalyzed by various CeO 2 nanocrystals was observed to follow the same reaction mechanism. C 2 H 2 adsorbs at both O and Ce sites on CeO 2 surfaces to form C 2 H 2 (a) species that facilely hydrogenates stepwise to C 2 H 3 (a) and C 2 H 4 (a). The surface hydrogenation reactions proceed more facilely at the O site than at the Ce site. The desorption of C 2 H 4 (a) proceeds slowly and is the rate-limiting step. c-CeO 2 , r-CeO 2 -500 and r-CeO 2 -700 do not exhibit obvious differences among these elementary surface reactions, but show much different abilities to dissociate H 2 and chemisorb C 2 H 2. The C 2 H 2 (a) coverage follows an order of r-CeO 2 -500 ≫ c-CeO 2 ≈ r-CeO 2 -700. The ability to dissociate H 2 follows an order of c-CeO 2 > r-CeO 2 -500 ≫ r-CeO 2 -700. The observed morphology-dependent behaviors of various CeO 2 nanocrystals were correlated to their defects and exposed facets. These results successfully demonstrate morphology-dependent CeO 2 catalysis in acetylene semihydrogenation reaction and elucidate the underlying mechanisms. [ABSTRACT FROM AUTHOR]