Probing zeolites by vibrational spectroscopies.

This review addresses the most relevant aspects of vibrational spectroscopies (IR, Raman and INS) applied to zeolites and zeotype materials. Surface Brønsted and Lewis acidity and surface basicity are treated in detail. The role of probe molecules and the relevance of tuning both the proton affinity and the steric hindrance of the probe to fully understand and map the complex site population present inside microporous materials are critically discussed.

Speciation of adsorbates on surface of solids by infrared spectroscopy and chemometrics.

Speciation, i.e. identification and quantification, of surface species on heterogeneous surfaces by infrared spectroscopy is important in many fields but remains a challenging task when facing strongly overlapped spectra of multiple adspecies.

On the mechanism of methanol photooxidation to methylformate and carbon dioxide on TiO2: an operando-FTIR study.

This work is a mechanistic study of total and partial methanol photooxidation using operando FTIR coupled to gas phase analysis techniques (gas-IR and MS). Methoxy and formate/formyl species play a key role in the reaction. Methoxy species are formed by thermal and photochemical dissociation of methanol.

Incorporation of clusters of titanium oxide in Beta zeolite structure by a new cold TiCl4-plasma process: physicochemical properties and photocatalytic activity.

A new post-synthetic approach, involving cold plasma treatment, was employed for the preparation of TiO2-Beta zeolite. Zeolite Beta nanoparticles were first subjected to plasma induced deposition of TiCly (with y≤ 3), which were further converted into TiOx (with x≤ 2) upon O2-plasma treatment. Different steps of the new elaborated plasma approach were monitored using in situ FTIR spectroscopy.

Effective bulk and surface temperatures of the catalyst bed of FT-IR cells used for in situ and operando studies.

The temperature prevailing in the catalyst bed of three different IR spectroscopic reaction cells was assessed by means of thermocouples, an optical pyrometer and reaction rate measurements. One of the cells was a custom-made transmission FT-IR cell for use with thin wafers and the two others were commercial Harrick and Spectra-Tech diffuse reflectance FT-IR (DRIFTS) cells used for the analysis of powdered samples. The rate of CO methanation measured over a 16 wt% Ni/alumina catalyst was used as a means to derive the effective temperature prevailing in the IR cells from that existing in a traditional (non-spectroscopic) reactor having a well-controlled temperature.

In situ FT-IR investigation of etravirine speciation in pores of SBA-15 ordered mesoporous silica material upon contact with water.

Ordered mesoporous silica (OMS) has been recognized as promising adsorbent material for drug molecules with low aqueous solubility. The release of drug molecules from OMS upon contact with aqueous environment enhances their oral bioavailability. The release is governed by a complex interplay of adsorption, diffusion, and intermolecular interaction inside OMS pores.

The porosity, acidity, and reactivity of dealuminated zeolite ZSM-5 at the single particle level: the influence of the zeolite architecture.

A combination of atomic force microscopy (AFM), high-resolution scanning electron microscopy (HR-SEM), focused-ion-beam scanning electron microscopy (FIB-SEM), X-ray photoelectron spectroscopy (XPS), confocal fluorescence microscopy (CFM), and UV/Vis and synchrotron-based IR microspectroscopy was used to investigate the dealumination processes of zeolite ZSM-5 at the individual crystal level. It was shown that steaming has a significant impact on the porosity, acidity, and reactivity of the zeolite materials. The catalytic performance, tested by the styrene oligomerization and methanol-to-olefin reactions, led to the conclusion that mild steaming conditions resulted in greatly enhanced acidity and reactivity of dealuminated zeolite ZSM-5.

Analysing and understanding the active site by IR spectroscopy.

IR spectroscopy is a technique particularly adapted for understanding the mechanism of catalytic reactions, being able to probe the surface mechanisms at the molecular level. In this critical review the main advances in the field are presented, both under the aspects of the in situ and operando approaches. A broad view of the most authoritative literature of the domain is given, based largely on the experience built up at the LCS laboratory in the last decades.

Microsecond time-resolved Fourier transform infrared analytics in a low pressure glow discharge reactor.

A low pressure glow discharge reactor has been designed to allow time-resolved infrared spectroscopic investigation of the discharge zone in practical conditions. The benefits of such reactor are demonstrated through the study of the evolution in the infrared spectra of air/CO(2) gas mixture at the microsecond time-scale. It has been shown that the spectra are greatly affected by the electrical discharge in the 2400-2200 cm(-1) region, where the asymmetric stretch mode of CO(2) falls.

Interaction of water and ammonium in NaHY zeolite as detected by combined IR and gravimetric analysis (AGIR).

Qualitative as well as quantitative information is obtained simultaneously by combining thermogravimetry and operando IR spectroscopy with on line mass spectrometry. A microbalance has been adapted to an infrared reactor cell. The weight and IR spectra of a solid sample can be measured together in real time in operando conditions, in a gas flow at temperature between room temperature and 773 K.

Real-time infrared detection of cyanide flip on silver-alumina NOx removal catalyst.

Spectroscopic studies of the mechanistic steps that occur on supported precious metal catalysts used in industrial and automotive applications are hampered by a dearth of suitable experimental methods. We used femtosecond laser excitation followed by nanosecond time-resolved in situ Fourier-transform infrared spectroscopy to initiate a catalytic reaction on alumina-supported silver catalysts, which are of interest in minimizing nitrogen oxide emissions from fuel-efficient lean-burn engines. We found that the key intermediate step in the reaction between carbon monoxide and nitric oxide is the flip of a cyanide group from a silver nanoparticle to the alumina support (with a lifetime of 2 microseconds), which indicates the central role played by the interface between the metal particle and the oxide support.

Infrared and microwaves at 5.8 GHz in a catalytic reactor.

An improved micro-reactor cell for IR spectroscopic studies of heterogeneous catalysis was built around a 5.8 GHz microwave cavity. The reactor can operate at 20 bars and with conventional heating up to 720 K, with reactant gas flows velocities (GHSV) from 25,000 to 50,000 h(-1).

Probing the Lewis acidity and catalytic activity of the metal-organic framework [Cu3(btc)2] (BTC=benzene-1,3,5-tricarboxylate).

An optimized procedure was designed for the preparation of the microporous metal-organic framework (MOF) [Cu3(btc)2] (BTC=benzene-1,3,5-tricarboxylate). The crystalline material was characterized by X-ray diffraction, optical microscopy, SEM, X-ray photoelectron spectroscopy, N2 sorption, thermogravimetry, and IR spectroscopy of adsorbed CO. CO adsorbs on a small number of Cu2O impurities, and particularly on the free CuII coordination sites in the framework.

NO2 disproportionation for the IR characterisation of basic zeolites.

NO2 disproportionation on alkaline zeolites is used to generate nitrosonium (NO+) and nitrate ions on the surface, and the infrared vibrations observed are very sensitive to the cation chemical hardness and to the basicity of zeolitic oxygen atoms.