Molecular chemistry of bimetallic clusters on the basic .gamma.-Al2O3 surface: synthesis, reactivity, and catalytic activity of [H3RuOs3(CO)12]-{Al} and related structures

Abstract

HzRuOs3(C0)13], [ H 4 R~O~3 ( C 0 ) 1 2 ] , [ Et4N] [HRUOS~(CO)~,], and [Et4N] [H3RuOs,(CO) were synthesized and characterized spectroscopically, and their reactivities with the basic -OH groups on the surface of y-Al,O, were investigated, the surface species being characterized by infrared and UV-vis spectroscopy and extraction of anions. Surface-bound anions were formed by adsorption of the salts. Alternatively, the surface-bound ion pair [HRuOs,(CO),,]-(AI) was formed from [H2R~O~3(C0)13] by deprotonation on the surface; the anion is bonded to the surface through a bridging carbonyl group interacting with a surface Lewis acid site (AI3+ ion). This surface anion is readily converted at 50-70 "C into [H3RuOs3(CO),,]-(A1), evidently by reacting with surface water. The latter anion is also formed by deprotonation of [H4RuOs3(CO),z] on the surface.[H,RuOs3(CO),,]-(Al] is the precursor of a catalyst for isomerization of but-1-ene to give cis-and trans-but-2-ene at 53-77 "C. The catalytic activity and the Langmuir-Hinshelwood kinetics parameters were the same, whether the catalyst was prepared by adsorption of [Et4] [H,RUOS~(CO)~,] or from [H2RuOs3(CO)13], converted into [HRuOs,(CO),,]-{Al) and then into [H3RuOs3(C0),,]-{A1).The catalyst was stable for >2000 turnovers. Infrared spectra showed that [H3RuOs3(CO),,]-(A1) was the predominant surface organometallic species on the working catalyst. When the catalyst was used instead for ethylene hydrogenation, the activity changed as the cluster was degraded; metal particles were formed, and these and/or mononuclear metal complexes are the likely catalytic species.The new field of surface organometallic is concerned with the synthesis, structure, reactivity, and catalytic activity of surface-bound analogues of molecular organometallic structures. The work is motivated3 by opportunities to use organometallic compounds as probes of the structure and reactivity of surface^,^ by opportunities offered by molecular organometallic precursors for formation of new surface structure^,'^^^^^^ and by prospects that these surface structures will have new catalytic p r o p e r t i e~.~%~,~-I~The "molecular" surface-bound organometallics are looked upon as models of the supported metal catalysts used in technology, such as the alumina-supported Pt-Re used in reforming of petroleum naphtha* and the oxide-supported Pt-Rh used in abatement of automobile e x h a~s t .~ These technological catalysts have highly complicated structures, incorporating aggregates (crystallites) of metal of various sizes and shapes dispersed on high-area porous metal oxide supports.Many of these supported metal catalysts used in technology are bimetallics;1° combinations of metals are often more effective catalysts than single metals. Consequently, there is interest in molecular bimetallic clusters as catalysts and catalyst precursors, in solution" and on supports.'* A number of molecular monometallic clusters have been anchored to the surfaces of metal oxide supports,I3 and a few of these have been investigated ...

Formation of a Manganese Tricarbonyl on the MgO Surface from Mn2(CO)10: Characterization by Infrared, Electron Paramagnetic Resonance, and X-ray Absorption Spectroscopies

“…We propose that the surface hydroxyl groups on MgO, which our IR spectra show reacted with the Mn 2 (CO) 10 , were the oxidizing agents. There are other examples of the oxidation of metals on oxide supports by surface hydroxyl groups, exemplified by the oxidation of ruthenium−osmium clusters on γ-Al 2 O 3 and of rhodium clusters on γ-Al 2 O 3 …”

Multimetallic Catalysis Based on Heterometallic Complexes and Clusters

“…After catalysis, [Al] + [H 3 RuOs 3 (CO) 12 ] − was the only detectable metal carbonyl species. 62 When attached to a polymeric support of the type (polym-NR 3 ) + , the cluster [Ph 4 As][H 3 RuOs 3 (CO) 12 ] was used for 1hexene hydroformylation. Under the reaction conditions, it appeared that isomerization to 2-hexene competed weakly.…”

The nature of hydrogen in γ-alumina

“…As such, the hydrogenated-spinel alumina phase will spontaneously decompose into the defective spinel phase and water. We also used the energies from PBE0 type of calculations at 0 K to assess the Gibbs free energy in reactions ( 6), (7), and (9). The result is consistent with the PBE type of calculations.…”

“…The calculated temperature dependencies of the Gibbs free energy changes for reactions (6), (7) and (9) are shown in Figure 5. Considering the change in the Gibbs free energy for the reaction (6) of decomposition of Boehmite into defective γ-alumina and water, the calculated critical temperature for the reaction is 678 K, in good agreement with the reaction temperature range from 673.15 to 723.15 K determined experimentally.…”

“…3,4 The γ-alumina phase has been extensively studied mostly due to its applications as a catalyst or catalyst support. [5][6][7][8] However, in spite of several experimental and theoretical works that have been devoted to the determination of its exact structure, the structure of γ-alumina is still not fully understood. 3,5,[9][10][11][12][13][14][15][16][17] The inherent poor crystallinity of γ-alumina, that can be prepared through various synthetic routes, significantly increases the difficulty of the problem.…”