Energy Dispersive Extended X-ray Absorption Fine Structure, Mass Spectrometric, and Diffuse Reflectance Infrared Studies of the Interaction of Al₂O₃-Supported Rh^I(CO)₂Cl Species with NO and Re-formation under CO

Abstract

The interaction between supported Rh I (CO) 2 Cl species, prepared by metallo-organic chemical vapor deposition (MOCVD) of [Rh(CO) 2 Cl] 2 to hydroxylated γ-Al 2 O 3 , and NO has been investigated using time-resolved, energy dispersive extended X-ray absorption fine structure (EDE)/mass spectrometry (MS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). MOCVD of [Rh I (CO) 2 Cl] 2 leads to the formation of a Rh I (CO) 2 Cl{O-Al} adlayer which, when fresh, reacts with NO to form a majority {Al-O} 2 RhCl(NO -) species at room temperature via a two-step mechanism involving an {Al-O}Rh(NO) 2 Cl species. The application of DRIFTS allows a direct association of the bent RhNO bonding in the {Al-O} 2 RhCl(NO)with "highwavenumber" Rh(NO -) species displaying ν(NO) at ca. 1750 cm -1 often observed in supported Rh systems. DRIFTS investigations on analogous Rh I (CO) 2 Cl/TiO 2 systems show the same reactivity toward NO, with a bent nitrosyl being formed rather than the more commonly dominant linear Rh(NO + ) species. DRIFTS also indicates that a second reaction is possible. This becomes increasingly significant for Rh(CO) 2 Cl{O-Al} samples exposed to air for ca. 2-3 days and results in the {Al-O}Rh I (CO) 2 Cl species reacting with NO to form a new species displaying adsorptions at 2150-2110 and 1750-1700 cm -1 . Once formed, this latter species reacts no further at room temperature under NO. The DRIFTS spectrum of this species is interpreted as being due to {Al-O}Rh(CO)(NO)Cl species existing in cis and trans configurations: the isomer with the carbonyl group trans to the Cl ligand being the preferred form at room temperature. The reconversion of the Rh(NO -) species under CO shows complex temperature dependence. The consumption of the Rh(NO -) shows only a weak temperature dependence in terms of EDE, but the observed evolution of NO g shows a strong temperature dependence. The combination of EDE and MS indicates rapid formation of an intermediate species, most likely {Al-O}Rh(CO)(NO)Cl, which at room temperature converts to the geminal dicarbonyl species slowly. The possible origins of this behavior, and the parameters determining the formation of "linear" and/ or "bent" rhodium nitrosyls in support Rh systems are discussed.

X-ray spectroscopy for chemistry in the 2-4 keV energy regime at the XMaS beamline: ionic liquids, Rh and Pd catalysts in gas and liquid environments, and Cl contamination in γ-Al2O3

“…], Evans et al, 2000Hayden et al, 1997Hayden et al, , 1998Newton et al, 2001, 2002[Newton, Burnaby et al, 2002or Newton, Jyoti et al, 2002; Newton et al, 2006;Bennett et al, 2007;Roscioni et al, 2013).…”

“…The volatile organo-metallic [Rh I (CO) 2 Cl] 2 serves as a useful probe molecule to assess both the Cl K-edge and Rh L 3 -edge XAS from a model system that has previously been well studied in terms of the basic chemistry it displays when supported upon metal oxide surfaces and high area supports such as -Al 2 O 3 (see, for instance, Frederick et al, 1987;Binsted et al, 1989;Evans et al, 1992a,b [ok? ], Evans et al, 2000Hayden et al, 1997Hayden et al, , 1998Newton et al, 2001, 2002[Newton, Burnaby et al, 2002or Newton, Jyoti et al, 2002; Newton et al, 2006;Bennett et al, 2007;Roscioni et al, 2013).…”

A Combined Multi-Technique In Situ Approach Used to Probe the Stability of Iron Molybdate Catalysts During Redox Cycling

“…The use of synchrotron light sources has, for a number of decades now, provided a way to examine catalysts under increasingly more realistic conditions [1][2][3][4][5][6]. The continued development of more brilliant and powerful light sources along with improved detectors has more recently allowed for the combination of two and three X-ray based in situ techniques [1,[7][8][9][10][11][12]. Information can now be collected on various parts of the catalyst congruently revealing additional insight into their operation under various conditions.…”

Understanding the role of promoters in catalysis: operando XAFS/DRIFTS study of CeOx/Pt/Al2O3 during CO oxidation

“…One limitation is the per atom average of the XAFS technique, which often fails to reflect the chemistry occurring at the surface of a catalyst, which is of course, where the catalysis happens. The combination of XAFS with surface sensitive techniques, such as diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), is able to provide a description of both the nanoparticle structure and the chemistry of the catalyst surface [10,11]. This study takes both approaches of controlled addition of promoters and combined spectroscopic techniques to assess the evolution of a CeO x /Pt/Al 2 O 3 catalyst during CO oxidation using simultaneous XAFS/DRIFTS acquisition.…”