Abstract: This paper reviews some of the aspects of combining in situ/operando infrared spectroscopy and kinetic studies. The strengths and limitations of various methods are discussed based on examples found in the literature and especially taken from the present author. A clear warning is made that qualitative or semi-quantitative analyses can easily result in unimportant surface species being mistaken for true reaction intermediates.

Abstract: The adsorption geometries, energies, and vibrational frequencies of methanol on MgO defective surfaces
have been calculated by periodic DFT simulations. The results are very comparable with those obtained with
water and are also in very good accordance with microcalorimetry and infrared experiments. At low coverage,
the dissociation is observed on all defects involving ions in low coordinations. Over and above the coordination
number of surface ions, the adsorption energy is strongly governed by the surface topology: dissociation on
confined sites gives rise to methoxy groups highly stabilized by bridging two or even three cations. The
occurrence of such very strong sites on MgO powder is confirmed by microcalorimetry. The dissociation
ability depends on the methanol coverage because it modifies the surface relaxation and the network of H
bonds, resulting, for a given defect, in similar adsorption energies for molecular and dissociated species at
high coverage. This explains why there are more strong sites (quantified by microcalorimetry) than dissociating
sites (quantified by infrared).

Abstract: The isomerization of o-xylene, a prototypical example of shape-selective catalysis by zeolites, was investigated on hierarchical porous ZSM-5. Extensive intra-crystalline mesoporosity in ZSM-5 was introduced by controlled silicon leaching with NaOH. In addition to the development of secondary porosity, the treatment also induced substantial aluminum redistribution, increasing the density of Lewis acid sites located at the crystals’ external surface. However, the strength of the remaining Brønsted sites was not changed. The mesoporous zeolite displayed a higher o-xylene conversion than its parent due to the reduced diffusion limitations. However, the selectivity to p-xylene decreased and fast deactivation due to coking occurred. This is mainly due to the deleterious effect of acidity at the substantially increased external surface and near the pore mouths. A consecutive mild HCl washing of the hierarchical zeolite proved effective to increase the p-xylene selectivity and reduce the deactivation rate. The HCl-washed hierarchical ZSM-5 displayed a ca. 2-fold increase in p-xylene yield compared to the purely microporous zeolite. The reaction was followed by operando infrared spectroscopy, in order to simultaneously monitor the catalytic performance and the build-up of carbonaceous deposits on the surface. Our results show that the interplay between activity, selectivity, and stability in modified zeolites can be optimized by relatively simple post-synthesis treatments, such as base leaching (introduction of mesoporosity) and acid washing (surface acidity modification).

Abstract: Fe–FER zeolites were characterized by FTIR spectroscopy of adsorbed CO and NO. Two aged samples (Fe–FER-1 and Fe–FER-4 with Fe content of 1.1 and 3.7 wt%, respectively) and one freshly prepared 57Fe rich sample (57Fe–FER, designed for Mössbauer studies and containing 1.5 wt% Fe) were studied. Both CO and NO are adsorbed onto Fe2+ cations and have different sensitivities to their location and/or coordination state. CO adsorption on Fe–FER-1 reveals two kinds of Fe2+ sites with the respective complexes observed at 2195 and 2189 cm−1. The principal carbonyls (2195 cm−1) are easily converted into dicarbonyls (2188 cm−1) at low temperature and high CO equilibrium pressure. NO is less sensitive than CO to the environment of Fe2+ ions and NO adsorption gives rise to a single band at 1878 cm−1. However, careful analysis reveals that this band consists of two closely located components. With the Fe–FER-4 sample a third family of iron sites was detected by CO at 2196 cm−1. These carbonyl species are stepwise converted to di- (not, vert, similar2188 cm−1) and tricarbonyls (not, vert, similar2180 cm−1). With these sites NO forms another nitrosyls clearly detected at 1895 cm−1. The latter are converted with time into polynitrosyls. These new sites are very sensitive to the preliminary treatment and easily change their oxidation state, forming Fe2+/Fe3+ redox couples. The sample preliminary treated with oxygen at 673 K is characterized by Fe3+–OH groups (3674 cm−1) and reactive oxygen that produces carbonates when reacting with CO, and NO+ when interacting with NO. Adsorption of NO on a freshly prepared 57Fe–FER sample confirms the presence of the three distinct Fe2+ sites which is consistent with Mössbauer data. Finally, summarizing all the data, location of the different sites inside the FER structure is proposed. The results obtained are discussed in relation with the catalytic performance of Fe–FER.

Abstract: The synthesis on the gram scale and characterization of a series of flexible functionalized iron terephthalate MIL-53(Fe) type solids are reported. Chemical groups of various polarities, hydrophilicities, and acidities (-Cl, -Br, -CF(3), -CH(3), -NH(2), -OH, -CO(2)H) were introduced through the aromatic linker, to systematically modify the pore surface. X-ray powder diffraction (XRPD), molecular simulations, thermogravimetric analyses, and in situ IR and (57)Fe Mossbauer spectrometries indicate some similarities with the pristine MIL-53(Fe) solid, with the adoption of the narrow pore form for all solids in both the hydrated and dry forms. Combined XRPD and computational structure determinations allow concluding that the geometry of the pore opening is predominantly correlated with the intraframework interactions rather than the steric hindrance of the substituent. Only (MIL-53(Fe)-(CF(3))(2)) exhibits a nitrogen accessible porosity (S(BET) approximately 100 m(2) g(-1)). The adsorption of some liquids leads to pore openings showing some very specific behaviors depending on the guest-MIL-53(Fe) framework interactions, which can be related to the energy difference between the narrow and large pore forms evaluated by molecular simulation.