MgO-supported bimetallic catalysts consisting of segregated, essentially molecular rhodium and osmium species

Abstract

A family of supported bimetallic samples was prepared by the reactions of Rh(C2H4)(acac) (acac = acetylacetonate) and Os3(CO)12 with MgO. The samples were characterized by infrared and extended X-ray absorption fine structure spectroscopies, before and after various treatments with hydrogen at temperatures up to 393 K. The spectra identify the following combinations of supported species: (a) [Os3(CO)11](2-) + Rh(C2H4)2, (b) [Os3(CO)11](2-) + Rh(CO)2, and (c) [Os3(CO)11](2-) + rhodium clusters containing approximately 4 to 6 atoms each, on average. No bimetallic clusters formed. The triosmium frame remained intact while the rhodium surface species were reduced in the presence of H2. The samples were tested as catalysts for ethylene hydrogenation at 298 K, and the catalytic activity matched that of the rhodium complexes alone; evidently the rhodium complexes were responsible for all the catalysis, with the osmium clusters remaining inactive because of the presence of the carbonyl ligands on them.

Bimetallic Sites for Catalysis: From Binuclear Metal Sites to Bimetallic Nanoclusters and Nanoparticles

“…At 333–398 K, the Ru–CO bonding is dissociated due to the reduction by H 2 and the formation of Ru–Os bonding is observed at temperature above 398 K. The EXAFS data indicate the formation of Ru 2 Os clusters after reduction treatment at 423 K. The formation of bimetallic clusters depends on the decomposition kinetics of the two metal precursors and the stability of the tiny metal clusters on the support. In the case of Rh and Os, the formation of bimetallic RhOs clusters is not observed when applying the H 2 reduction treatment to MgO-supported Os 3 (CO) 12 and Rh­(C 2 H 4 )­(acac) (acac = acetylacetonate) complex at temperature up to 393 K. Because of the lower stability of Rh­(C 2 H 4 )­(acac), the formation of Rh 4–6 clusters is observed after reduction treatment at 393 K while the Os 3 (CO) 12 species remain intact under the same conditions . Consequently, the formation of small RhOs clusters will be more difficult than the case of RuOs.…”

“…In the case of Rh and Os, the formation of bimetallic RhOs clusters is not observed when applying the H 2 reduction treatment to MgOsupported Os 3 (CO) 12 and Rh(C 2 H 4 )(acac) (acac = acetylacetonate) complex at temperature up to 393 K. Because of the lower stability of Rh(C 2 H 4 )(acac), the formation of Rh 4−6 clusters is observed after reduction treatment at 393 K while the Os 3 (CO) 12 species remain intact under the same conditions. 91 Consequently, the formation of small RhOs clusters will be more difficult than the case of RuOs. Therefore, one strategy to facilitate the contact between the two metals is to use bimetallic complexes as the precursor for impregnation.…”

Determination of the electronic and structural configuration of coordination compounds by synchrotron-radiation techniques

“…Over the years, Gates and co-workers have synthesized many metal complexes on various supports and determined their structure and catalytic performance [865][866][867][868][869][870][871][872][873][874][875][876]. They highlighted that the support has a strong and defining influence on the structure of the complex or particle and as a result on the catalytic performance [877].…”