The review is a summary and analysis of the data characterizing CO adsorption on surface cationic sites of oxides including supported materials and microporous and mesoporous materials. The contributions of various types of CO bonding to the IR frequency shifts of carbon-bonded molecules are analyzed, namely, the increase of the CO stretching frequency in cases of electrostatic and σ bonding and the decrease of the frequency with π bonding. Polycarbonyls, bridging CO, oxygen-bonded CO, and tilted CO are also considered. The main part of the review is a collection of the experimental results characterizing carbonyls of individual metal ions. The spectral behavior of CO bonded to metal atoms is also assessed in the cases when the metal ions are easily reduced to metal (Cu, Ag, Au, Pd, or Pt) or cationic carbonyls are produced after CO adsorption on supported metals (Ru, Rh, Ir, and Os). The interaction of CO with surface OH groups is also considered. It is demonstrated that IR spectroscopy of adsorbed CO is an efficient methodology to characterize cationic surface sites in terms of their nature, oxidation states, coordination environment and coordinative unsaturation, and location at faces, edges or corners of microcrystallites. When applied to materials with surface hydroxyl groups CO undergoes hydrogen bonding and information can be collected on the proton acid strength.

Characterization of oxide surfaces and zeolites by carbon monoxide as an IR probe molecule

Gas adsorption experiments have been carried out on a copper benzene tricarboxylate metal-organic framework material, HKUST-1. Hydrogen adsorption at 1 and 10 bar (both 77 K) gives an adsorption capacity of 11.16 mmol H2 per g of HKUST-1 (22.7 mg g(-)1, 2.27 wt %) at 1 bar and 18 mmol per g (36.28 mg g(-)1, 3.6 wt %) at 10 bar. Adsorption of D2 at 1 bar (77 K) is between 1.09 (at 1 bar) and 1.20(at <100 mbar) times the H2 values depending on the pressure, agreeing with the theoretical expectations. Gravimetric adsorption measurements of NO on HKUST-1 at 196 K (1 bar) gives a large adsorption capacity of approximately 9 mmol g(-1), which is significantly greater than any other adsorption capacity reported on a porous solid. At 298 K the adsorption capacity at 1 bar is just over 3 mmol g(-1). Infra red experiments show that the NO binds to the empty copper metal sites in HKUST-1. Chemiluminescence and platelet aggregometry experiments indicate that the amount of NO recovered on exposure of the resulting complex to water is enough to be biologically active, completely inhibiting platelet aggregation in platelet rich plasma.

High-capacity hydrogen and nitric oxide adsorption and storage in a metal-organic framework

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Reactivity of Surface Species in Heterogeneous Catalysts Probed by In Situ X-ray Absorption Techniques

This critical review describes the reactivity of heterogeneous catalysts from the point of view of four simple, but essential for Chemistry, molecules (namely dihydrogen, carbon monoxide, nitrogen monoxide and ethylene) that are considered as probes or as reactants in combination with “in situ” controlled temperature and pressure Infrared spectroscopy. The fundamental properties of H2, CO, NO and C2H4 are shortly described in order to justify their different behaviour in respect of isolated sites in different environments, extended surfaces, clusters, crystalline or amorphous materials. The description is given by considering some “key studies” and trying to evidence similarities and differences among surfaces and probes (572 references).

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Probing the surfaces of heterogeneous catalysts by in situ IR spectroscopy

The structure of active centers and the ethylene polymerization mechanism on the Cr/SiO2 catalyst: a frontier for the characterization methods.

XAFS, IR, and UV−vis (diffuse reflectance and photoluminescence) spectroscopies have been employed to investigate the local environment of CuI in CuI-ZSM-5 prepared by gas phase reaction of H-ZSM-5 (SiO2/Al2O3 = 90−50) with CuCl The measurements confirm that the absolutely predominant copper species formed with this procedure are CuI:Cu species in other oxidation states are less than 1% Direct proof of the absence of both unreacted CuCl microaggregates and of copper clusters in the zeolite channels is also given CuI-ZSM-5 prepared in this way represents a model solid for investigating the structure of isolated CuI sites in zeolites EXAFS analysis reveal that, in vacuum conditions, Cu+ cations are surrounded by 25 ± 03 oxygens at 200 ± 002 A The combined use of EXAFS, IR, and photoluminescence UV−vis spectroscopies and computer graphic simulations allows to infer that Cu+ ions in CuI-ZSM-5 are located in two families of sites, indicated as I and II, (site II having the highest coordinative unsatur

XAFS, IR, and UV−Vis Study of the CuI Environment in CuI-ZSM-5

IR and XAFS have been employed to investigate the local environment of Cu 1 in Cu 1 -ZSM-5 prepared by gas phase reaction of H-ZSM-5 with CuCI. Both XAFS and IR measurements show that copper species are momodispersed Cu ions occupying highly unsaturated sites easily accessible to small ligand molecules. Cu 1 -ZSM-5 prepared in this way represent a model solid for investigating the structure of isolated Cu I sites in zeolites. EXAFS analysis reveal that, in vacuum conditions, Cut cations are surrounded by 2.5 ± 0.3 oxygens at 2.00 ± 0.02 A. The combined use of EXAFS, IR and computer graphic simulations allows to infer that Cu I ions in Cu I -ZSM-5 are located in two families of sites.

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M. Bellatreccia

Papers

XAFS, IR, and UV−Vis Study of the CuI Environment in CuI-ZSM-5

CuI Sites in CuI–ZSM–5 : A XAFS, IR and Computer Graphics Study