Quantitative determination of surface species and adsorption sites using Infrared spectroscopy

McCue, Alan J.; Mutch, Greg A.; McNab, A.; Campbell, Steven; Anderson, James A.

doi:10.1016/j.cattod.2015.03.039

Cited by 36 publications

(31 citation statements)

References 54 publications

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“…Spectra and the total mass due to pyridine adsorption were recorded at both temperatures which then permits absorption coefficients for bands due to two independent modes of vibration for Lewis and Brønsted bound pyridine to be determined. The values of the absorption coefficients then permits the individual numbers of Brøn-sted and Lewis acid sites to be determined [24]. Although signal to noise ratio in some samples was lower than ideal, determination of molar absorption coefficients using the above methodology permitted a cross-check that these were consistent with published values [24] and thus a degree of confidence in the values obtained for the densities of the of Brønsted and Lewis acid sites was afforded.…”

Section: Acid Site Density Determinationmentioning

confidence: 83%

Mechanistic Insights into the Desorption of Methanol and Dimethyl Ether Over ZSM-5 Catalysts

et al. 2017

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The desorption of methanol and dimethyl ether has been studied over fresh and hydrocarbon-occluded ZSM-5 catalysts with Si/Al ratios of 25, 36 and 135 using a temporal analysis of products reactor. The catalysts were characterized by XRD, SEM, N 2 physisorption and pyridine FT-IR. The crystal size increases with Si/Al ratio from 0.10 to 0.78 µm. The kinetic parameters were obtained using the Redhead method and a plug flow reactor model with coupled convection, adsorption and desorption steps. ZSM-5 catalysts with Si/Al ratios of 25 and 36 exhibit three adsorption sites (low, medium, and high temperature sites), while there is no difference between medium and high temperature sites at a Si/Al ratio of 135. Molecular adsorption on the low temperature site and dissociative adsorption on the medium and high temperature sites give a good match between experiment and the plug flow reactor model. The DME desorption activation energy was systematically higher than that of methanol. Adsorption stoichiometry shows that methanol and DME form clusters onto the binding sites. When non-activated re-adsorption is accounted for, a local equilibrium is reached only on the low and medium temperature binding sites. No differences were observed, other than in site densities, when extracting the kinetic parameters for fresh and activated ZSM-5 catalysts at full coverage. Graphical AbstractElectronic supplementary material The online version of this article (https://doi

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Section: Acid Site Density Determinationmentioning

confidence: 83%

Mechanistic Insights into the Desorption of Methanol and Dimethyl Ether Over ZSM-5 Catalysts

et al. 2017

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“…Herein, the conditions necessary to induce Pd surface segregation for CuPd catalysts are described along with how this can be used to enhance their activity for acetylene hydrogenation. FTIR spectroscopy is used to quantitatively monitor surface composition [52] and apparent changes are related to changes in catalyst activity/selectivity. It is thought the method described herein could be readily adapted to study other bimetallic systems and allow for a correlation between surface composition and catalytic properties to be established.…”

Section: Introductionmentioning

confidence: 99%

CO induced surface segregation as a means of improving surface composition and enhancing performance of CuPd bimetallic catalysts

McCue

Anderson

2015

Journal of Catalysis

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a b s t r a c tA series of copper rich CuPd/Al 2 O 3 catalysts were prepared and characterised by FTIR spectroscopy using CO as a probe molecule. After reduction, the surface composition was largely composed of Cu with evidence of a small concentration of isolated Pd atoms. It was found that CO induced surface segregation could be used to increase the surface Pd concentration and depending on the Cu:Pd ratio, the formation of Pd-Pd dimers was possible. Changes in surface composition were quantified and correlated with catalyst activity and selectivity for selective acetylene hydrogenation. For the catalyst with optimum Cu:Pd ratio (50:1), it was possible to use CO induced segregation to increase activity considerably (20 K temperature reduction to achieve 100% conversion) whilst only marginally affecting ethylene selectivity (%5% decrease in ethylene selectivity). An estimate of the detection limit by FTIR of the minimum surface coverage of isolated Pd and Pd-Pd dimers is given.

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“…The result is consistent with those obtained by using XPS. Another band at

\overset{ν}{true}

=1910–1900 cm −1 , which is observed clearly in the spectra of Rh/CeO 2 ‐I and ‐G, is assigned to bridging CO on Rh 0 or on the Rh–Ce interface ,–. As these catalysts showed a relatively low band intensity of CO adsorbed linearly on Rh 0 and as our XPS analysis indicated that the Rh 0 fractions of these samples are relatively low, we assumed that the bridging CO in the spectra of on Rh/CeO 2 ‐I and ‐G is caused by bridging CO adsorption on the interface between rhodium oxide species and CeO 2 .…”

Section: Resultsmentioning

confidence: 99%

Formation of Rhodium Metal Ensembles that Facilitate Nitric Oxide Reduction over Rhodium/Ceria in a Stoichiometric Nitric Oxide–Carbon Monoxide–Propene–Oxygen Reaction

2018

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A series of ceria‐supported Rh nanoparticles (NPs) that have various particle sizes of 2–7 nm was prepared to investigate the size effect of Rh NPs on NO reduction in NO–CO–C3H6–O2 under stoichiometric conditions. The turnover frequency (TOF) for NO reduction on Rh NPs increased drastically according to their particle size. The strong size dependence of the TOF was attributed to the oxidation states of Rh NPs but not to particle geometries, which include fractions of surface local sites (e.g., corner, edge, plane) and the surface crystal structures (e.g., Rh(1 1 1), (1 0 0)). The variation of the TOF with the Rh metal fraction suggested that Rh metal ensembles are highly active species for NO reduction.

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Quantitative determination of surface species and adsorption sites using Infrared spectroscopy

Cited by 36 publications

References 54 publications

Mechanistic Insights into the Desorption of Methanol and Dimethyl Ether Over ZSM-5 Catalysts

Mechanistic Insights into the Desorption of Methanol and Dimethyl Ether Over ZSM-5 Catalysts

CO induced surface segregation as a means of improving surface composition and enhancing performance of CuPd bimetallic catalysts

Formation of Rhodium Metal Ensembles that Facilitate Nitric Oxide Reduction over Rhodium/Ceria in a Stoichiometric Nitric Oxide–Carbon Monoxide–Propene–Oxygen Reaction

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