Catalysis and Spectrochemistry Laboratory

Accurate assessment of the metal dispersion is known to be important in the field of catalysis, as these data are used to calculate the turnover frequency of a given reaction on a given metal. This study shows that N2 can be used as an FTIR probe molecule not only qualitatively but also quantitatively. For the first time, it is found that the integrated molar absorption coefficient of N2 adsorbed on the HAp supports (epsilonN2-HAp = 0.092±0.008 cm/µmol) does not depend on the chemical composition of HAp, while that of N2 adsorbed on the HAp-supported Ru0 nanoparticles of about 2.2 nm (epsilonN2-Ru0: 0.5-1.03 cm/µmol) is sensitive to the chemical composition of HAp. This study also shows, for the first time, that epsilonN2-Ru0 increases with increasing electron density of the Ru0 nanoparticles, as monitored by the position of the maximum of the absorption band of the N2 stretching vibration at about 2200 cm-1 (nuN2-Ru0), with a remarkable correlation between epsilonN2-Ru0 and nuN2-Ru0. The epsilonN2-Ru0 data are two orders of magnitude smaller than the previously reported integrated molar absorption coefficients of CO (epsilonCO-Ru0). Finally, epsilonN2-HAp and epsilonN2-Ru0 allow us to estimate the Ru dispersion, which is in remarkable agreement with that determined by TEM.

Germanium-containing zeolites (Ge-MFI) offer significant potential for catalytic applications, owing to their unique structural properties such as extra-large porosity, facilitated by a broader range of Ge–O–Si angles and Ge–O bonds compared to the Al–O–Si, Al–O, and Si–O found in conventional aluminosilicate zeolites. This study highlights the catalytic performance of the Ge-MFI catalyst in the ring-opening reaction of propylene oxide, an essential step in synthesizing value-added chemicals. Employing in situ and operando FTIR spectroscopy, we investigated the reaction mechanism and product distribution, uncovering how propylene oxide interacts with Ge-based Lewis acid sites and induces group migration that facilitates molecular reorganization. This work demonstrates that incorporating germanium into the MFI framework produces a highly stable and selective catalyst with discrete Lewis acid sites, activated at 450 °C. The catalyst achieved a conversion of 37% at 400 °C, markedly outperforming its siliceous counterpart (Si-MFI catalyst), which reached only 16%. Furthermore, the Ge-MFI catalyst exhibited superior selectivity toward propionaldehyde, attaining 85% at 350 °C compared to 35% for Si-MFI under identical conditions.

Abstract Hybrid vibration energy harvesting technology converts vibration energy into electricity using multiple transduction mechanisms to improve output power. A frequency‐tunable resonant hybrid vibration energy harvester using a piezoelectric cantilever with electret‐based electrostatic coupling is proposed in this article. The electrostatic coupling including electrostatic force coupling and electrical damping coupling is introduced by an electret film placed below the cantilever, where the electrostatic force acting on the cantilever realises a tunable resonant frequency and additional electrical damping boosts power output. A coupling electromechanical model is derived using Euler–Bernoulli beam theory and Kirchhoff's law. By investigating the static and dynamic stability of cantilever, the maximum electret surface potential is defined to prevent the pull‐in phenomenon. The damping of the device is evaluated, and the optimal electret surface potential is determined to obtain the matching of the electrical and mechanical damping for maximum power output. The resonant frequency of hybrid vibration energy harvester can be adjusted in range of 176.1 rad/s by changing the electret surface potential and resistive load. The experimental output power of hybrid vibration energy harvester was 5.2 μW, 27.4 times higher than that of the individual piezoelectric generator. The proposed hybrid vibration energy harvester exhibits a promising potential to power microelectronic devices and wireless sensor network node.

Abstract Metal–Organic Frameworks (MOFs) with open metal sites (OMS) interact strongly with a range of polar gases/vapors. However, under ambient conditions, their selective adsorption is generally impaired due to a high OMS affinity to water. This led previously to the privilege selection of hydrophobic MOFs for the selective capture/detection of volatile organic compounds (VOCs). Herein, we show that this paradigm is challenged by metal(III) polycarboxylates MOFs, bearing a high concentration of OMS, as MIL‐100(Fe), enabling the selective capture of polar VOCs even in the presence of water. With experimental and computational tools, including single‐component gravimetric and dynamic mixture adsorption measurements, in situ infrared (IR) spectroscopy and Density Functional Theory calculations we reveal that this adsorption mechanism involves a direct coordination of the VOC on the OMS, associated with an interaction energy that exceeds that of water. Hence, MOFs with OMS are demonstrated to be of interest for air purification purposes.

Abstract Encapsulating ultrasmall Cu nanoparticles inside Zr‐MOFs to form core–shell architecture is very challenging but of interest for CO2reduction. We report for the first time the incorporation of ultrasmall Cu NCs into a series of benchmark Zr‐MOFs, without Cu NCs aggregation, via a scalable room temperature fabrication approach. The Cu NCs@MOFs core–shell composites show much enhanced reactivity in comparison to the Cu NCs confined in the pore of MOFs, regardless of their very similar intrinsic properties at the atomic level. Moreover, introducing polar groups on the MOF structure can further improve both the catalytic reactivity and selectivity. Mechanistic investigation reveals that the CuIsites located at the interface between Cu NCs and support serve as the active sites and efficiently catalyze CO2photoreduction. This synergetic effect may pave the way for the design of low‐cost and efficient catalysts for CO2photoreduction into high‐value chemical feedstock.

The purification of biofuels becomes a challenging issue because of the harmfulness of remaining phenolic molecules for human health and engines. To this end, protonic Y zeolites with different Si/Al ratios were explored as effective adsorbent materials to remove phenol from isooctane solution by using a dual experimental/computational strategy. Phenol was selectively removed from isooctane over HY and USY zeolites with a maximal adsorption capacity of 2.2 mmol·g–1, which corresponds to 3–4 phenol molecules per zeolitic supercage. The adsorption equilibrium was reached faster over dealuminated zeolites, due to the presence of large pores at the expense of microporosity as well as a low density of acidic sites. We further evidence that the presence of acid sites limits the regeneration capacity since phenol was strongly adsorbed on both Bronsted and Lewis acid sites. USY zeolite with the highest Si/Al ratio presents the best regeneration capacity since it has the lower aluminum loading. A fundamental under...

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Catalysts based on tungsten oxide supported on silica and containing up to 2.5 W atoms nm–2 were studied for the purpose of establishing quantitative relationships between the nature and abundance of surface species, acidity, and catalytic activity. Synthesis conditions that maximize the formation of amorphous WO3 were adopted to assess its influence on the overall acidity and activity. The results were compared to those of conventionally prepared catalysts. The catalysts’ structure was characterized by FTIR, Raman, and UV spectroscopies. The acidity of the solids was monitored by adsorption of 2,6-dimethylpyridine followed by FTIR, and their catalytic activity was tested for the reaction of propan-2-ol dehydration. A methodology for quantitation of W species (WOx surface species, amorphous or crystalline WO3 particles) detected following calcination at 673 or 773 K was developed. For both calcination temperatures, surface W species were first formed with initial W addition. Their abundance increased with increasing W content up to ca. 0.7 atom W nm–2 and levels off for higher W surface densities. The leveling off was concomitant with the detection and rapid development of amorphous or crystalline WO3 phase (catalysts calcined respectively at 673 or 773 K). The comparison of W speciation in both series indicated that amorphous WO3 phase is quantitatively transformed to crystalline WO3 on increasing the calcination temperature from 673 to 773 K. The observed development of Brønsted acidity of the solids was associated with W deposition. The abundance of these acid sites correlated directly with the catalytic activity. The study of structure–activity relationship showed that all W species were active. Modeling of the results permitted an estimation of the intrinsic activity of each W species. The values thus obtained suggest that amorphous WO3 particles exhibit the highest activity per surface W atom.