Investigating the Acid Site Distribution of a New-Generation Methyl Chloride Synthesis Catalyst

McInroy, Alastair R.; Winfield, John M.; Dudman, Christopher C.; Jones, Peter N.; Lennon, David

doi:10.1021/acsomega.9b01719

Cited by 4 publications

(16 citation statements)

References 18 publications

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“…In the context of the emerging operando movement within the heterogeneous catalysis research community, the DRIFTS sampling option enjoys wide popularity [37]. However, this study reiterates the point made by Holmes et al, that one should be aware that different IR sampling arrangements can affect spectral outcomes [20].…”

Section: Drifts Comparison On Nicolet Spectrometersupporting

confidence: 56%

A Comparison of Experimental Procedures for the Application of Infrared Spectroscopy to Probe the Surface Morphology of an Alumina-Supported Palladium Catalyst

et al. 2021

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Structure/function relationships in heterogeneous catalysis play an important role in catalyst design strategies. The combination of chemisorption of suitable probe molecules alongside application of infrared spectroscopy is an established technique for providing information on the metal crystallite morphology of supported metal catalysts. Following a review of key literature on this topic, a variety of experimental arrangements that may be adopted for this task are examined. Specifically, the adsorption of CO over a 5wt% Pd/Al2O3 catalyst is investigated using transmission and diffuse reflectance sampling options and two research grade spectrometers. Although comparable spectra are obtained on all the platforms examined, differences are noted. In particular, temperature-programmed IR spectroscopy on one platform enables resolution of two features assigned to linear CO bound to the Pd particles. The relevance of this sub-division of terminal sites with respect to selective hydrogenation reactions is briefly considered.

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Section: Drifts Comparison On Nicolet Spectrometersupporting

confidence: 56%

A Comparison of Experimental Procedures for the Application of Infrared Spectroscopy to Probe the Surface Morphology of an Alumina-Supported Palladium Catalyst

et al. 2021

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“…Therefore, the majority of the published articles concerning the acidity measurements of catalysts used IR spectroscopy of pyridine and TG and/or DSC TPD of NH 3 to quantify total acidity. [ 1 , 3 , 45 , 46 ] Our calculated results of the TG‐TPD experiments using THF, as shown in Table 1 , were approximately 1.6‐2.7 times those calculated using TG‐TPD of pyridine over the four samples. The higher the population of the THF molecules over the sample surface, hence an accurate calculation of the total accessible acidic sites will be achieved.…”

Section: Resultsmentioning

confidence: 57%

“…In a recently published paper, [18] based on their findings, the authors suggested that infrared (IR) spectroscopy of Pyr can be used to qualitatively identify the different types of acidic sites, but it was unable to accurately determine these sites quantitatively. Therefore, the majority of the published articles concerning the acidity measurements of catalysts used IR spectroscopy of pyridine and TG and/or DSC TPD of NH 3 to quantify total acidity [1,3,45,46] . Our calculated results of the TG‐TPD experiments using THF, as shown in Table 1, were approximately 1.6‐2.7 times those calculated using TG‐TPD of pyridine over the four samples.…”

Section: Resultsmentioning

confidence: 76%

Assessment of Lewis‐Acidic Surface Sites Using Tetrahydrofuran as a Suitable and Smart Probe Molecule

et al. 2022

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Measuring the Lewis‐acidic surface sites in catalysis is problematic when the material‘s surface area is very low (SBET ≤1 m2 ⋅ g−1). For the first time, a quantitative assessment of total acidic surface sites of very small surface area catalysts (MoO3 as pure and mixed with 5–30 % CdO (wt/wt), as well as CdO for comparison) was performed using a smart new probe molecule, tetrahydrofuran (THF). The results were nearly identical compared to using another commonly used probe molecule, pyridine. This audition is based on the limited values of the surface area of these samples that likely require a relatively moderate basic molecule as THF with pKb=16.08, rather than strong basic molecules such as NH3 (pKb=4.75) or pyridine (pKb=8.77). We propose mechanisms for the interaction of vapour phase molecules of THF with the Lewis‐cationic Mo and Cd atoms of these catalysts. Besides, dehydration of isopropyl alcohol was used as a probe reaction to investigate the catalytic activity of these catalysts to further support our findings in the case of THF in a temperature range of 175–300 °C. A good agreement between the obtained data of sample MoO3‐10 % CdO, which is characterised by the highest surface area value, the population of Lewis‐acidic sites and % selectivity of propylene at all the applied reaction temperatures was found.

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“…These changes to the spectral profile correlate with a previous deduction from McInroy et al that group 1 metal dopant levels of ≥0.6 mmol CsCl g (cat) –1 effectively neutralize the strong and medium-strong Lewis acid sites of η-alumina, leaving only medium-weak and weak Lewis acid sites accessible. 4 The changes in the spectra of KCl-doped catalysts are similar, but the reduction in the intensity of the negative peak is less, implying a smaller effect of KCl on catalyst properties.…”

Section: Resultsmentioning

confidence: 93%

“… 3 Subsequent studies used the same probe molecule to evaluate how the group 1 metal chlorides were able to neutralize selectively Lewis acid sites of the η-alumina to effect site-selective chemistry that is associated with attenuated DME production ( eq 2 ). 4 The present work concentrates on using methanol as a spectroscopic probe molecule to discern how the group 1 metal chloride may be perturbing the surface chemistry of the reagent. Thus, the work does not directly investigate aspects of methyl chloride synthesis catalysis; rather, it represents a fundamental study of methanol adsorption on catalytically relevant surfaces.…”

Section: Introductionmentioning

confidence: 99%

Interaction of Methanol over CsCl- and KCl-Doped η-Alumina and the Attenuation of Dimethyl Ether Formation

McInroy

Winfield

Dudman³

et al. 2022

J. Phys. Chem. C

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As part of a program to investigate aspects of surface chemistry relevant to methyl chloride synthesis catalysis, the interaction of methanol with η-alumina doped with either CsCl or KCl in the range 0.01–1.0 mmol g (cat) –1 is investigated by a combination of diffuse reflectance infrared Fourier transform spectroscopy and temperature-programed desorption (TPD). Infrared spectra (IR) recorded at 293 K show that increasing the concentration of the group 1 metal chloride progressively decreases the surface concentration of associatively chemisorbed methanol and changes the environment in which the adsorbed methanol resides. For CsCl concentrations of ≥0.6 mmol g (cat) –1 , chemisorbed methoxy species dominate the IR spectrum, while TPD studies show that the amount of methanol adsorbed onto the surface, and subsequently desorbed unchanged, changes relatively little. In the TPD experiments, some of the adsorbed methanol reacts to give dimethyl ether (DME) which then desorbs; for dopant concentrations of 1.0 mmol g (cat) –1 , DME formation is suppressed to below the limit of detection. Unexpectedly, the presence of formate species generated at 293 K is also observed spectroscopically, characterized by a ν asym (COO) mode which exhibits a hypsochromic shift relative to potassium formate; surface concentrations of formate are higher at higher loadings of group 1 metal chloride. Temperature-programed IR spectroscopy shows that the room-temperature formate species desorbs, decomposes, or migrates on warming to 653 K. Thermal ramping of the methanol-saturated surface also results in formate production but one that exhibits an IR profile in agreement with earlier observations and literature values. Increasing the concentrations of the group 1 metal chloride progressively decreases the presence of the thermally induced formate moiety. The study not only reinforces the concept of group 1 metal chloride additives progressively rendering ineffective those Lewis acid sites present at the η-alumina surface which convey discrete reaction characteristics [ e.g. , (i) dimerization of methanol to form DME and (ii) an activated methoxy → formate transition] but also suggests the generation of reactive sites not present in the undoped alumina.

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Investigating the Acid Site Distribution of a New-Generation Methyl Chloride Synthesis Catalyst

Cited by 4 publications

References 18 publications

A Comparison of Experimental Procedures for the Application of Infrared Spectroscopy to Probe the Surface Morphology of an Alumina-Supported Palladium Catalyst

A Comparison of Experimental Procedures for the Application of Infrared Spectroscopy to Probe the Surface Morphology of an Alumina-Supported Palladium Catalyst

Assessment of Lewis‐Acidic Surface Sites Using Tetrahydrofuran as a Suitable and Smart Probe Molecule

Interaction of Methanol over CsCl- and KCl-Doped η-Alumina and the Attenuation of Dimethyl Ether Formation

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