Françoise Maugé

Parallel between infrared characterisation and ab initio calculations of CO adsorption on sulphided Mo catalysts

Abstract Carbon monoxide adsorption on sulphided Mo catalysts has been investigated by means of IR spectroscopy and DFT ab initio calculations. IR experiments show that CO adsorption on the sulphide phase of Mo/Al2O3 catalysts gives rise to various ν(CO) bands, the intensities of which are strongly modified when post-treatment of the catalyst with H2 or H2S is performed before CO adsorption, therefore, revealing strong modifications in the nature and the number of sites present on the sulphide phase. Ab initio periodic DFT calculations allow to define two types of edges for MoS2, which sulphur coverage and structure depend on the H2/H2S ratio in the surrounding atmosphere. Adsorption energies and stretching wavenumber of CO adsorbed on the various sites of these surfaces were computed, providing the possibility to compare for the first time results from theoretical calculations and spectroscopic measurements on these systems. A novel attribution of the main IR features of CO adsorbed on MoS2 is proposed.

FT-IR study of co adsorption on sulfided Mo/Al2O3 unpromoted or promoted by metal carbonyls: Titration of sites

Abstract The IR study of CO adsorption at low temperature has been used to follow the transformation of unpromoted Mo sites into promoted ones on sulfided Mo/Al 2 O 3 catalysts. The promotion is realized by thermal decomposition of different amounts of Co(CO) 3 NO on sulfided Mo/Al 2 O 3 . The determination of integrated molar extinction coefficients of the η(CO) bands corresponding to the different sites has been performed. For the unpromoted catalyst, the titration technique used leads to a number of Mo sites, which is in good agreement with that provided from the geometrical model. Evidence that the formation of one promoted site occurs at the expense of one unpromoted site is provided. However, the number of detected promoted sites is lower than that expected from the amount of cobalt introduced: introduction of six cobalt atoms leads to the creation of only one promoted site. The migration of cobalt atoms into intercalated positions or into alumina is considered.

The sulphided state of nickel molybdenum catalysts supported on zirconia and aluminates

Abstract Characterization of the sulphided Ni-MoS 2 state supported on various carriers (aluminates, zirconia) has been undertaken in order to study the influence of the carrier on the genesis of the promoted active phase, refered to as the “NiMoS” phase. The influence of the sulphidation temperature on the stability of nickel associated in that phase has also been explored. The basis of comparison is a classical Ni-MoS 2 -alumina catalyst. In all these systems nickel interacts with molybdenum sulphide (decoration like position) but the “NiMoS” phase appears less stable on zirconia. On these aluminate and zirconia carriers, the charge transfer from nickel to molybdenum sulphide, as evidenced by the shifts of the active IR band of adsorbed carbon monoxide, has been found to be weaker than on the alumina supported catalyst. Such a carrier effect has been correlated with thiophene HDS activity results and discussed in terms of morphological effects as revealed by HREM.

New aspects of catalytic functions on sulfide catalysts

Abstract The influence of Co on the acidic properties (Lewis and Bronsted) of molybdenum sulfide catalyst were determined by infrared studies of adsorbed pyridine or 2,6-dimethylpyridine. These studies show that the promoter addition increases the strength of the Lewis sites and the number of Bronsted sites. These results are correlated to those obtained for dibenzothiophene conversion. For this reaction, it was observed that the influence of the promoter is very different for the two different routes involved in the reaction scheme. Consequently, the role of the promoter is not only to increase the number of sulfur vacancies but also to modify the acid–base properties of the catalyst.

Surface properties of zirconia catalyst carriers : interaction with oxomolybdates species

Abstract The oxidic precursor of molybdenum based catalysts supported on stabilized zirconia and on zirconia stabilized titania have been characterized by laser Raman (LRS) and Fourier transform infrared (FT-IR) spectroscopy and by X-ray photoelectron spectroscopy (XPS). Analysis of the supports by LRS and X-ray diffraction showed that the tetragonal form of zirconia and the anatase form of titania were stabilized. Deposition of oxomolybdate species does not modify the properties of these supports and a monolayer like coverage up to 7 Mo at.nm−2 and 5 Mo at.nm−2 was obtained on zirconia and TiO2-ZrO2-, respectively. Nickel added by impregnation was shown to interact with the supported oxomolybdate species as well as nickel from a ZrO2-NiO support.

Basic sites on mixed nitrided galloaluminophosphates "AlGaPON": infrared studies of SO2 and CDCl3 adsorption

The basic properties of nitrided galloaluminophosphate “AlGaPON” are documented by FTIR of sulphur dioxide and deuterated chloroform. To evidence the increase in the number of basic sites with nitrogen enrichment, we compared the spectra recorded after adsorption of CDCl3 on the phosphate precursor “AlGaPO” and on four oxynitrides with increasing nitrogen contents. On the oxide, adsorption arises from CDCl3 interacting with surface hydroxyl groups, on the oxynitrides basic sites are shown to be M–NH2 groups. This interpretation is confirmed by FTIR of adsorbed SO2.

The pivotal role of catalysis in France: selective examples of recent advances and future prospects

The Review describes the most significant results achieved in France in the field of heterogeneous catalysis over the last 10 years and placed in the context of international research. The focus lies on the research conducted in French academic laboratories, often in close collaboration with industrial partners. A wide range of heterogeneous catalysis is covered, including ab initio calculations, biomass conversion, catalytic cracking, catalyst characterization, CO2 conversion, Fischer–Tropsch, pollution abatement, power‐to‐gas and kinetics.