Paramagnetic metal and oxygen species observed when alumina-(or zirconia-supported rhodium, Rh/γ-Al2O3(ZrO2), is obtained by the decarbonylation of [Rh4(CO)12]-Al2O3(ZrO2) are discussed as a function of the decarbonylation temperature (250–600 °C) and the method of decarbonylation (pyrolysis in vacuo or reduction in an H2 stream). On vacuum-pyrolysed samples, RhP(T)/γ-Al2O3, RhIIformal centres are stable only after decarbonylation at 250 °C; contact with O2 produces [RhIIIn–O2]˙–(n= 1,2) and Al3+—O2–, with an increasing amount of Al3+—O–2 as the decarbonylation temperature increases. RhP(T)/ZrO2 does not show paramagnetic species before contact with O2: the treatment with O2 stabilizes both [Rh2III—O2]˙– and Zr4+—O–2centres at a decarbonylation temperature of 250 °C, while essentially Zr4+—O2– alone is formed at higher temperature. On H2 reduced samples, RhH(T)/γ-Al2O3, formal RhO centres formed in the decarbonylation temperature range 250–500 °C, while no paramagnetic species were observed on RhH(T)/ZrO2. Contact with O2 shows behaviour of RhH(T)/γ-Al2O3(ZrO2) very similar to that of RhP(T)/γ-Al2O3(ZrO2). The stability of the Rh—O2 bond is a function of the metal positive charge and it is related to the decarbonylation temperature. The strength of the interaction between O2–and the support acidic centres, Al3+ and Zr4+, is always high inγ-Al2O3-supported samples, and dramatically increases in ZrO2-supported samples on increasing the decarbonylation temperature. Different pathways of electron transfer can explain the observed behaviour of Rh/ZrO2.

Paramagnetic metal and oxygen species observed with RH/gamma AL203 and RH/ZRO2 : dependence on the decarbonylation temperature of [RH4(CO)12] on alumina and zirconia supports / A. Gervasini, F. Morazzoni, D. Strumolo, F. Pinna, G. Strukul, L. Zanderighi. - In: JOURNAL OF THE CHEMICAL SOCIETY. FARADAY TRANSACTIONS I. - ISSN 0300-9599. - 82:6(1986), pp. 1795-1804. [10.1039/f19868201795]

Paramagnetic metal and oxygen species observed with RH/gamma AL203 and RH/ZRO2 : dependence on the decarbonylation temperature of [RH4(CO)12] on alumina and zirconia supports

A. Gervasini
Primo
;
D. Strumolo;
1986

Abstract

Paramagnetic metal and oxygen species observed when alumina-(or zirconia-supported rhodium, Rh/γ-Al2O3(ZrO2), is obtained by the decarbonylation of [Rh4(CO)12]-Al2O3(ZrO2) are discussed as a function of the decarbonylation temperature (250–600 °C) and the method of decarbonylation (pyrolysis in vacuo or reduction in an H2 stream). On vacuum-pyrolysed samples, RhP(T)/γ-Al2O3, RhIIformal centres are stable only after decarbonylation at 250 °C; contact with O2 produces [RhIIIn–O2]˙–(n= 1,2) and Al3+—O2–, with an increasing amount of Al3+—O–2 as the decarbonylation temperature increases. RhP(T)/ZrO2 does not show paramagnetic species before contact with O2: the treatment with O2 stabilizes both [Rh2III—O2]˙– and Zr4+—O–2centres at a decarbonylation temperature of 250 °C, while essentially Zr4+—O2– alone is formed at higher temperature. On H2 reduced samples, RhH(T)/γ-Al2O3, formal RhO centres formed in the decarbonylation temperature range 250–500 °C, while no paramagnetic species were observed on RhH(T)/ZrO2. Contact with O2 shows behaviour of RhH(T)/γ-Al2O3(ZrO2) very similar to that of RhP(T)/γ-Al2O3(ZrO2). The stability of the Rh—O2 bond is a function of the metal positive charge and it is related to the decarbonylation temperature. The strength of the interaction between O2–and the support acidic centres, Al3+ and Zr4+, is always high inγ-Al2O3-supported samples, and dramatically increases in ZrO2-supported samples on increasing the decarbonylation temperature. Different pathways of electron transfer can explain the observed behaviour of Rh/ZrO2.
Settore CHIM/02 - Chimica Fisica
1986
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/195732
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