Quantifying adsorption thermodynamics on heterogeneous catalysts remains challenging because macroscopic techniques yield averaged parameters, while vibrational spectra often contain strongly overlapping contributions from multiple adsorbed species. Here we introduce an infrared (IR)-chemometric framework that extracts site-specific adsorption thermodynamics directly from experimental IR isotherms and we benchmark it against independent microcalorimetry and density functional theory (DFT) calculations. Difference IR spectra recorded for isobutanol adsorption on H-ZSM-5 (MFI) were analysed by principal component analysis and multivariate curve resolution (MCR-ALS) under soft constraints (monotonic concentration profiles, spectral normalisation), and further refined using a hard-soft strategy in which concentration profiles are constrained by an adsorption model. The analysis reveals three adsorption modes associated with bridging Br & oslash;nsted OH groups, extra-framework Al-OH species, and silanols, providing representative pure-component spectra and site-resolved adsorption isotherms. The thermodynamic trends and site hierarchy obtained from IR-MCR-ALS are consistent with independent microcalorimetry measurements and density functional theory calculations, validating the approach. More broadly, IR-MCR-ALS offers a transferable route to quantitative, site-resolved adsorption thermodynamics in complex catalysts.

The surface chemistry of amorphous silica is governed by the concentration, environment, and accessibility of silanol groups, yet quantitative comparison between closely related silica samples remains challenging due to surface heterogeneity and overlapping spectroscopic signatures. In this study, infrared spectroscopy is combined with H-D isotopic exchange and size-selective molecular probes to speciate isolated, internal, and associated silanol populations across a series of silica samples with similar composition but differing surface characteristics. A dilution effect in surface silanol density with increasing specific surface area was observed, and notable batch-to-batch variability further highlights the sensitivity of silanol speciation to subtle differences in material preparation. Nominally similar silicas can exhibit pronounced differences in silanol distribution and accessibility, including measurable batch-to-batch variability that is not reflected by BET surface area or total hydroxyl content. Internal and associated silanols represent a substantial fraction of the total hydroxyl population and display variable accessibility to probe molecules. These findings suggest that global surface descriptors alone are insufficient for describing silica surface chemistry and that explicit consideration of silanol speciation and accessibility is required for reliable interpretation of spectroscopic and chemical measurements.

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The selective dehydration of isobutanol to linear butenes catalyzed by acidic ferrierite (H-FER) has been investigated by operando IR spectroscopy under close batch conditions and along a temperature ramp. The employed apparatus permits to alternatively acquire spectra of both the gas phase composition and the species adsorbed on the H-FER surface, thus providing fundamental insights onto the products formation and the reaction intermediates formed on the catalyst surface. In the gas phase, the high selectivity for linear butenes was confirmed in the first phases of the reaction, followed by a slower isomerization to isobutene and by the formation of heavier compounds due to secondary processes. Detailed MCR-ALS analysis of the adsorbed species’ spectra permitted to also identify and quantify adsorbed 2-butanol and trans-2-butene on the H-FER surface, providing a first indication of the alcohol isomerization as a key step in the reaction mechanism. The proposed mechanism was evaluated by microkinetic modelling of both gas phase and surface concentration profiles, showing that the consecutive isomerization of isobutanol to adsorbed 2-butanol followed by its dehydration to trans-2-butene is more favorable than the one-step dehydration-isomerization of isobutanol. In contrast, the direct dehydration of isobutanol to isobutene was found to be slower over the entire investigated temperature range.

The surface chemistry of amorphous silica is governed by the concentration, environment, and accessibility of silanol groups, yet quantitative comparison between closely related silica samples remains challenging due to surface heterogeneity and overlapping spectroscopic signatures. In this study, infrared spectroscopy is combined with H-D isotopic exchange and size-selective molecular probes to speciate isolated, internal, and associated silanol populations across a series of silica samples with similar composition but differing surface characteristics. A dilution effect in surface silanol density with increasing specific surface area was observed, and notable batch-to-batch variability further highlights the sensitivity of silanol speciation to subtle differences in material preparation. Nominally similar silicas can exhibit pronounced differences in silanol distribution and accessibility, including measurable batch-to-batch variability that is not reflected by BET surface area or total hydroxyl content. Internal and associated silanols represent a substantial fraction of the total hydroxyl population and display variable accessibility to probe molecules. These findings suggest that global surface descriptors alone are insufficient for describing silica surface chemistry and that explicit consideration of silanol speciation and accessibility is required for reliable interpretation of spectroscopic and chemical measurements.

This study investigates the mechanisms of CO2 capture by Li4SiO4 employing in situ Fourier transform infrared spectroscopy (FT-IR) combined with multivariate data analysis, with particular attention being paid to the influence of structural modifications derived from natural diatomite on the CO2 sorption performance of Li4SiO4. Three samples were examined: a reference Li4SiO4 material synthesized from pure SiO2 (SiO2-LS), a stoichiometric mixture using calcined diatomite (ND-LS) and an over-stoichiometric sample containing 10% calcined diatomite (10% ND-LS). FTIR analysis confirmed the formation of carbonate species during CO2 uptake. Chemometric analysis using principal component analysis (PCA) and multivariate curve resolution-alternating least squares (MCR-ALS) allowed identification of the successive formation of two distinct carbonate species (species 1 and species 2), supporting the double-shell carbonation model. In ND-derived samples, a distinct band at 1140 cm-1, attributed to the symmetric stretching vibration (ν1) of a carbonate species associated with magnesium carbonates, was identified. The presence of surface MgCO3 associated with species 1 in ND-derived samples was found to enhance CO2 capture kinetics by facilitating carbonate layer formation through interfacial diffusion pathways. This study provides valuable insights into the carbonation mechanisms of Li4SiO4, demonstrating that calcined diatomite improves CO2 uptake efficiency and opening new perspectives for the optimization of lithium silicate-based CO2 sorbents through targeted compositional modifications.

We report the development of a new method of investigation of the mass transport properties of acidic zeolite-based materials aiming to overcome the limitations of classical approaches. It consists in hyphenating gravimetric analysis and infrared spectroscopy. The former allows assessing the diffusion from the gas phase to all the porosity, while IR allows for selective assessment of diffusion to the zeolite active sites located in the micropores. Furthermore, the data are processed by an original methodology allowing the recovery of the distribution of diffusion domains by inversion of the integral equations describing the uptake curves or the evolution of the infrared spectra. The combination of gravimetric analysis and IR spectroscopy makes it possible to monitor and distinguish diffusion within the various components of the material. The methodology has been applied to the isooctane uptake in the mechanical mixture of FAU and MFI zeolites. Analysis of both gravimetric uptake curves and evolving infrared spectra allows distinguishing and assigning diffusion domains to the H-FAU and H-MFI components of the mixture, with high and low effective diffusion rate constants, respectively. The advantages and limits of the methodology are discussed.

The one-step catalytic conversion of bio-based ethanol to 1,3-butadiene is an attractive way to produce this important C4 building block, to be exploited as a sustainable drop-in chemical in the tire and nylon industry. For this catalytic process, bifunctional catalysts combining both redox and acidic properties are required. Here, we leverage non-hydrolytic sol-gel (NHSG) chemistry to prepare tailored Cu-Ta-SiO2 catalysts featuring an open texture, dispersed acidic Ta sites, and small Cu nanoparticles. In the ether route, silicon tetrachloride and tantalum pentachloride undergo polycondensation reactions with diisopropyl ether as the oxygen donor. In the acetamide elimination route, silicon tetraacetate reacts with pentakis(dimethylamido)tantalum(V). In both routes, copper(II) acetylacetonate is added and trapped in a tantalosilicate matrix. Upon calcination, CuO nanoparticles form and the resulting bifunctional material develop a mesoporous texture with specific surface areas in the 650-950 m(2) g(-1) range, pore volumes between 0.75 and 0.90 cm(3) g(-1), and average pore diameters above 3 nm. With the help of NH3-TPD, FTIR, CO- and pyridine-adsorbed FTIR, XRD, XPS, and STEM-EDS, we demonstrate that the catalysts made via the acetamide elimination route show higher performance in the ethanol-to-butadiene reaction, with low selectivity in dehydration byproducts, owing to moderate Lewis acidity, smaller Cu nanoparticles, and higher active site proximity. After optimization of the Ta and Cu loadings, a butadiene productivity as high as 0.38 g(BD) g(cat)(-1) h(-1) is obtained, surpassing state-of-the-art catalysts with similar formulations and tested under similar reaction conditions.

For the tailoring purpose of NiMgAl-oxides (NMA) towards CO2 methanation, the surfactant Pluronic-P123 was first-time employed at different concentrations. Catalysts were examined by SEM-EDX, BET, XRD, H2-TPR, CO2-TPD, and TGA. By adding P123, a clear revolution in terms of the texture, morphology, and pore of catalysts was observed, which has never been recorded previously. The correlations between carbonate species and basic sites were identified thanks to in-situ CO2 sorption measurements. The stability of carbonate species was assumed to follow "hydrogen-carbonate < bidentate-carbonate < unidentate-carbonate < tridentate-carbonate". On the activity stand, 3P-NMA exhibited ca. 83.5% CO2 conversion and 99.5% CH4 selectivity at 300 celcius vs. 46% and 97%, respectively, for the base case (GHSV = 12,000 h-1, H2/CO2 = 4), alongside superior stability after a 16 h of TOS run. Furthermore, Operando FTIR data revealed the appearance of formyl (*HCO) species under methanation conditions, allowing us to propose the reaction mechanism following *HCO formation as the key intermediate for CO2 methanation.

In this work, we investigated cyclohexane oxidative dehydrogenation (ODH) catalyzed by cobalt ferrite nanoparticles supported on reduced graphene oxide (RGO). We aim to identify the active sites that are specifically responsible for full and partial dehydrogenation using advanced spectroscopic techniques such as X-ray photoelectron emission microscopy (XPEEM) and X-ray photoelectron spectroscopy (XPS) along with kinetic analysis. Spectroscopically, we propose that Fe3+/T(d )sites could exclusively produce benzene through full cyclohexane dehydrogenation, while kinetic analysis shows that oxygen-derived species (O*) are responsible for partial dehydrogenation to form cyclohexene in a single catalytic sojourn. We unravel the dynamic cooperativity between octahedral and tetrahedral sites and the unique role of the support in masking undesired active (Fe3+/T-d) sites. This phenomenon was strategically used to control the abundance of these species on the catalyst surface by varying the particle size and the wt % content of the nanoparticles on the RGO support in order to control the reaction selectivity without compromising reaction rates which are otherwise extremely challenging due to the much favorable thermodynamics for complete dehydrogenation and complete combustion under oxidative conditions.

CO2 methanation is an attractive reaction to convert CO2 into a widespread fuel such as methane, being the combination of catalysts and a dielectric barrier discharge (DBD) plasma responsible for synergistic effects on the catalyst’s performances. In this work, a Ru-based zeolite catalyst, 3Ru/CsUSY, was synthesized by incipient wetness impregnation and characterized by TGA, XRD, H2-TPR, N2 sorption and CO2-TPD. Catalysts were tested under thermal and plasma-assisted CO2 methanation conditions using in-situ operando FTIR, with the aim of comparing the mechanism under both types of catalysis. The incorporation of Ru over the CsUSY zeolite used as support induced a decrease of the textural properties and an increase of the basicity and hydrophobicity, while no zeolite structural damage was observed. Under thermal conditions, a maximum CO2 conversion of 72% and CH4 selectivity above 95% were registered. These promising results were ascribed to the presence of small Ru0 nanoparticles over the support (16 nm), catalyst surface hydrophobicity and the presence of medium-strength basic sites in the catalyst. Under plasma-catalytic conditions, barely studied in similar setups in literature, CO2 was found to be excited by the plasma, facilitating its adsorption on the surface of 3Ru/CsUSY in the form of oxidized carbon species such as formates, aldehydes, carbonates, or carbonyls, which are afterwards progressively hydrogenated to methane. Adsorption and surface reaction of key intermediates, namely formate and aldehydic groups, was observed even on the support alone, an occurrence not reported before for thermal catalysis. Overall, similar reaction mechanisms were proposed for both thermal and plasma-catalysis conditions.

Dual templating approach, using hexadecyltrimethylammonium bromide (CTAB), was employed in an attempt to synthesize hierarchical ZSM-5 zeolite. Amount of mesoporogen and the duration of aging of the precursor were varied. Majority of the synthesis routes resulted in phase separation, yielding separate ZSM-5 and amorphous mesoporous material. The relative amounts of the two phases were dependent on the CTAB amount ratio and also significantly on the duration of precursor aging before CTAB addition. One particular combination of the two factors led to the formation of a homogeneous hierarchical form of ZSM-5 with leafy morphology, consisting of intergrown thin crystalline sheets which formed flower-like structures. The hierarchical ZSM-5 possessed significant microporous (approximate to 95 m2/g) and highly developed mesoporous surface (approximate to 470 m2/g), with a relatively broad distribution of mesopore sizes (<20 nm). The acidity of all samples was studied in detail. Isothermal microcalorimetry/volumetry of ammonia adsorption provided quantitative data on the number and distribution of strength of acidic sites. In situ FTIR of pyridine and collidine adsorption was used to quantify Bronsted and Lewis acid sites, and to provide information on their location - in the micropores or mesopores/external surface. The hierarchical ZSM-5 possessed both Lewis and Bronsted acidity, with Bronsted sites located mainly in the micropores. All samples were fully characterized using XRD, low temperature nitrogen adsorption, FESEM and EDS. The synthetic route used for obtaining the ZSM-5 zeolite with flower-like morphology is a simple strategy for preparing hierarchical ZSM-5 forms targeting enhanced diffusivity and accessibility of catalytically active sites.

Ourin situ operandoIR DBD cell makes it possible to study the surface species formed in a plasma-catalytic system.

The CO2 capture represents a major technical challenge to fight against global warming. Adsorption is an interesting alternative for CO2 capture. The use of oxides to enhance the CO2 adsorption over zeolites is largely pointed out in the literature. This study, dedicated to MgO-impregnated NaY zeolite, is based on CO2 adsorption and desorption over this adsorbent at various MgO rates (2, 5, 10, and 15 %) via in situ FTIR spectroscopy. This later provides very useful information about the physisorbed and chemisorbed CO2 according to MgO impregnation rate. FTIR investigation, based on adsorption at 25 degrees C of low and high doses of CO2, then followed by desorption under vacuum at 25, 100, and 200 degrees C, indicates that CO2 is physically adsorbed on cationic sites and chemically in the form of carbonates. The major carbonate species formed are bicarbonate, unidentate, chelated and bridged bidentate carbonate as well as carboxylate species. The results show that the chelated bidentate carbonate, and carboxylate species are the most resistant to desorption, which is related to both basicity and accessible porosity. In addition, this investigation highlights the heterogeneity of zeolites due to the formation of various adsorption basic sites.

The conversion of isobutanol to light olefins over zeolites was investigated by IR operando spectroscopy. FER zeolites showed a surprisingly high selectivity for the direct conversion of iso-butanol to linear butenes, hence catalyzing dehydration and skeletal isomerization in one step. As a fundamental understanding of the separate reactions is required to design superior catalysts, an in situ and operando FT-IR mechanistic study of the reaction was carried out. The spectroscopic data, the derived species participating and their respective role are analyzed using chemometric (PCA and MCR-ALS) tools. We highlighted the role played by the external acid sites and the requirement of a specific distance between these sites to ensure the n-butene selectivity and point that the internal Brunsted acidity has an adverse effect on the catalyst stability. Moreover, there is no correlation between the carbon species formed on the surface and the exceptional selectivity towards n-butenes, allowing to exclude a "carbon pool" mechanism.