Changes of Pd Oxidation State in Pd/Al2O3 Catalysts Using Modulated Excitation DRIFTS

Chiarello, Gian Luca; Lu, Yonglai; Agote-Arán, Miren; Pellegrini, Riccardo; Ferri, Davide

doi:10.3390/catal11010116

Cited by 6 publications

(5 citation statements)

References 33 publications

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“…In fact, besides significant noise reduction, such an approach allows discrimination between active and spectator species and, thus, a focus on the crucial aspects of the mechanism. In heterogeneous catalysis, MES has been mostly used to study reactions of small molecules, e.g., CO oxidation, − NH 3 –SCR (selective catalytic reduction), − and CO 2 activation, − but to the best of our knowledge, there has been no application in the context of the economically important field of alkane oxidation catalysis.…”

Section: Introductionmentioning

confidence: 99%

Unraveling the Active Vanadium Sites and Adsorbate Dynamics in VO_x/CeO₂ Oxidation Catalysts Using Transient IR Spectroscopy

2022

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The oxidative dehydrogenation (ODH) of propane over supported vanadia catalysts is an attractive route toward propene (propylene) with the potential of industrial application and has been extensively studied over decades. Despite numerous mechanistic studies, the active vanadyl site of the reaction has not been elucidated. In this work, we unravel the ODH reaction mechanism, including the nuclearity-dependent vanadyl and surface dynamics, over ceriasupported vanadia (VO x /CeO 2 ) catalysts by applying (isotopic) modulation excitation IR spectroscopy supported by operando Raman and UV−vis spectroscopies. Based on our loading-dependent analysis, we were able to identify two different mechanisms leading to propylene, which are characterized by isopropyland acrylate-like intermediates. The modulation excitation IR approach also allows for the determination of the time evolution of the vanadia, hydroxyl, and adsorbate dynamics, underlining the intimate interplay between the surface vanadia species and the ceria support. Our results highlight the potential of transient IR spectroscopy to provide a detailed understanding of reaction mechanisms in oxidation catalysis and the dynamics of surface catalytic processes in general.

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Section: Introductionmentioning

confidence: 99%

Unraveling the Active Vanadium Sites and Adsorbate Dynamics in VO_x/CeO₂ Oxidation Catalysts Using Transient IR Spectroscopy

2022

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“…This indicates that PdO can efficiently adsorb CO molecules. The small peaks at 2129, 2102, and 1955 cm –1 correspond to CO linearly adsorbed on Pd + , linearly adsorbed on metallic Pd, and bridge-bound on metallic Pd, respectively. − The presence of Pd + and Pd 0 may be due to partially reduced Pd species under a CO atmosphere. , These results suggest that PdO/ZSM-5 significantly enhances the adsorption capacity for CO compared to ZSM-5, promoting the activation of CO, which may contribute to the carbonylation process.…”

Section: Resultsmentioning

confidence: 94%

Boosting the Production of Glycolic Acid from Formaldehyde Carbonylation via the Bifunctional PdO/ZSM-5 Catalyst

Cao,

Zhang,

Wang

et al. 2023

Ind. Eng. Chem. Res.

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The carbonylation of formaldehyde offers a promising, cost-effective, and environmentally friendly method for synthesizing glycolic acid, a crucial monomer in biodegradable plastics. This study highlights the development and optimization of a bifunctional PdO/ZSM-5 zeolite catalyst for this process. Investigations via various spectroscopic techniques reveal that Pd species, predominantly in the form of PdO, enhance the CO activation, thereby boosting the formaldehyde carbonylation reaction rate significantly. The optimal catalytic performance was observed with a Pd-loading of 2 wt %. Notably, excessive Pd loading was found to impede the catalytic performance by overoccupying acid sites, thereby reducing its capacity to activate formaldehyde. The concurrent activation of formaldehyde and CO at the Brønsted acid site and the PdO site, respectively, through a Langmuir–Hinshelwood mechanism is key to the enhanced catalytic performance. These findings underscore the importance of CO activation in improving the formaldehyde carbonylation process, offering vital insights for catalyst optimization.

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“…XAS quantifies the oxidation state of the bulk. Complementary techniques such as IR, XPS, [82,83] or Raman [24] are necessary to quantify the percentage of a specific oxidation state on the surface. In EXAFS, it is impossible to distinguish between scattering atoms with little difference in atomic number: C, N, O or S, Cl, or Mn and Fe, for example.…”

Section: Detection Limits Quantitative Analyses and Wavelet Transformmentioning

confidence: 99%

Experimental methods in chemical engineering:X‐ray absorption spectroscopy—XAS,XANES,EXAFS

et al. 2021

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Although X-ray absorption spectroscopy (XAS) was conceived in the early 20th century, it took 60 years after the advent of synchrotrons for researchers to exploit its tremendous potential. Counterintuitively, researchers are now developing bench type polychromatic X-ray sources that are less brilliant to measure catalyst stability and work with toxic substances. XAS measures the absorption spectra of electrons that X-rays eject from the tightly bound core electrons to the continuum. The spectrum from 10 to 150 eV (kinetic energy of the photoelectrons) above the chemical potential-binding energy of core electrons-identifies oxidation state and band occupancy (X-ray absorption near edge structure, XANES), while higher energies in the spectrum relate to local atomic structure like coordination number and distance, Debye-Waller factor, and inner potential correction (extended X-ray absorption fine structure, EXAFS). Combining XAS with complementary spectroscopic techniques like Raman, Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) elucidates the nature of the chemical bonds at the catalyst surface to better understand reaction mechanisms and intermediates. Because synchrotrons continue to be the light source of choice for most researchers, the number of articles Web of Science indexes per year has grown from 1000 in 1991 to 1700 in 2020. Material scientists and physical chemists publish an order of magnitude articles more than chemical engineers. Based on a bibliometric analysis, the research comprises five clusters centred around: electronic and optical properties, oxidation and hydrogenation catalysis, complementary analytical techniques like FTIR, nanoparticles and electrocatalysis, and iron, metals, and complexes.

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Changes of Pd Oxidation State in Pd/Al2O3 Catalysts Using Modulated Excitation DRIFTS

Cited by 6 publications

References 33 publications

Unraveling the Active Vanadium Sites and Adsorbate Dynamics in VO_x/CeO₂ Oxidation Catalysts Using Transient IR Spectroscopy

Unraveling the Active Vanadium Sites and Adsorbate Dynamics in VO_x/CeO₂ Oxidation Catalysts Using Transient IR Spectroscopy

Boosting the Production of Glycolic Acid from Formaldehyde Carbonylation via the Bifunctional PdO/ZSM-5 Catalyst

Experimental methods in chemical engineering:X‐ray absorption spectroscopy—XAS,XANES,EXAFS

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Changes of Pd Oxidation State in Pd/Al2O3 Catalysts Using Modulated Excitation DRIFTS

Cited by 6 publications

References 33 publications

Unraveling the Active Vanadium Sites and Adsorbate Dynamics in VOx/CeO2 Oxidation Catalysts Using Transient IR Spectroscopy

Unraveling the Active Vanadium Sites and Adsorbate Dynamics in VOx/CeO2 Oxidation Catalysts Using Transient IR Spectroscopy

Boosting the Production of Glycolic Acid from Formaldehyde Carbonylation via the Bifunctional PdO/ZSM-5 Catalyst

Experimental methods in chemical engineering:X‐ray absorption spectroscopy—XAS,XANES,EXAFS

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Unraveling the Active Vanadium Sites and Adsorbate Dynamics in VO_x/CeO₂ Oxidation Catalysts Using Transient IR Spectroscopy

Unraveling the Active Vanadium Sites and Adsorbate Dynamics in VO_x/CeO₂ Oxidation Catalysts Using Transient IR Spectroscopy