Phosphonic acid modifiers for enhancing selective hydrodeoxygenation over Pt catalysts: The role of the catalyst support

Coan, Patrick D.; Griffin, Michael B.; Ciesielski, Peter N.; Medlin, J. Will

doi:10.1016/j.jcat.2019.03.011

Cited by 27 publications

(21 citation statements)

References 48 publications

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“…Another key effect of PA modification is the potential to decrease the number of active sites through site-blocking effects. Previous work has shown that PA modification of TiO 2 introduces some new Brønsted acid sites (as measured by infrared spectroscopy after pyridine adsorption) but sharply decreases the total number of (Lewis) acid sites as measured by ammonia TPD. , Perhaps the clearest indication of a decrease in the number of available active sites comes from the TPRS experiments. As shown in Figure , both unreacted alcohol desorption yield and (especially) the dehydration product yield were substantially decreased by the PA SAMs.…”

Section: Discussionmentioning

confidence: 99%

Effects of Phosphonic Acid Monolayers on the Dehydration Mechanism of Aliphatic Alcohols on TiO₂

Ballesteros–Soberanas

Ellis

Medlin

2019

ACS Catal.

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The kinetics for surface-catalyzed alcohol dehydration reactions often depends on the structure of the alcohol. Studies of structure-activity relations across primary, secondary, and tertiary alcohols can provide fundamental information on the nature of active sites on the surface. Here, we investigated the dehydration of 1-butanol, 2-butanol and tert-butanol over TiO2 anatase catalysts modified with various phosphonic acid (PA) self-assembled monolayers (SAMs). As a response to the presence of PAs, the three C4 alcohol isomers showed different dehydration rates, with 1-butanol dehydration being enhanced to the greatest extent by PA modification. Furthermore, the fluorinated, more polar 4-fluorobenzyl phosphonic acid outperformed alkyl PAs across all alcohols. Steady-state kinetic measurements and temperature programmed desorption studies indicated that PA SAMs significantly lowered the dehydration activation barrier; the extent of reduction in the barrier was sensitive to both the substitution of the alcohol and the charge distribution on the PA in a way that was consistent with stabilization of a carbenium-like transition state. Overall, the effect of PA modifiers on alcohol dehydration rates was found to be determined from a balance between transition state stabilization and active site blocking effects, with the potential to tune activity and selectivity based on the structure and coverage of the SAM.

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Section: Discussionmentioning

confidence: 99%

Effects of Phosphonic Acid Monolayers on the Dehydration Mechanism of Aliphatic Alcohols on TiO₂

Ballesteros–Soberanas

Ellis

Medlin

2019

ACS Catal.

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“…In considering ways to tune this type of promoting effect, one might expect that the electronic properties of the ligand would play a role and, in particular, that its acidity (or conjugate basicity) would be important. Previous work has shown that modification of Pd/Al 2 O 3 and other supported metal catalysts with alkyl PAs creates Brønsted acid sites on the catalyst. ,, In the prior work, temperature-programmed pyridine DRIFTS studies were used to show that the acidity of the catalyst could be tuned via changing the acidity of the PA precursor and that use of more acidic PAs improved activity for reactions such as HDO that are known to occur at the metal-support interface. However, most of the acidic sites monitored in those studies were associated with binding to the catalyst support rather than the metal.…”

Section: Discussionmentioning

confidence: 99%

Organic Modifiers Promote Furfuryl Alcohol Ring Hydrogenation via Surface Hydrogen-Bonding Interactions

et al. 2021

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Interactions between surface adsorbed species can affect catalyst reactivity, and thus, the ability to tune these interactions is of considerable importance. Deposition of organic modifiers provides one method of intentionally introducing controllable surface interactions onto catalyst surfaces. In this study, Pd/Al2O3 catalysts were modified with either thiol or phosphonic acid (PA) ligands and tested in the hydrogenation of furanic species. The thiol modifiers were found to inhibit ring hydrogenation (RH) activity, with the degree of inhibition trending with the thiol surface coverage. This suggests that thiols do not strongly interact with the reactants and simply serve to block active sites on the Pd surface. PAs, on the other hand, were found to enhance RH when furfuryl alcohol (FA) was used as the reactant. Density functional theory calculations suggested that this enhancement was due to hydrogen-bonding interactions between FA-derived surface intermediates and PA modifiers. Here, installation of hydrogen-bonding groups on the Pd surface served to preferentially stabilize RH product states. Furthermore, the promotional effect on the RH of FA was observed to be greater when a higher-coverage PA was used, providing a rate more than twice that of the unmodified Pd/Al2O3. The results of this work suggest that organic ligands can be designed to impart tunable surface interactions on heterogeneous catalysts, providing an additional method of controlling catalytic performance.

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“…Organophosphonic acids (PAs) are a promising alternative for the grafting of metal oxide surfaces, as discussed in various reviews [28][29][30] and by the study of PA-modified materials in a 4 variety of technological domains such as membrane separation 6,7,31 , supported metal catalysis [32][33][34]35 , hybrid (photo)electric devices 36 , implant materials 10,13 and chromatography. [37][38][39][40] In contrast to organosilanes, PAs are much less susceptible towards self-condensation (i.e.…”

Section: Introductionmentioning

confidence: 99%

Experimental and computational insights into the aminopropylphosphonic acid modification of mesoporous TiO2 powder: The role of the amine functionality on the surface interaction and coordination

Gys

Siemons

Pawlak

et al. 2021

Applied Surface Science

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Recently, interest has been directed towards the grafting of metal oxides with organophosphonic acids bearing terminal amine groups to extend the functionality and applicability of these materials. Previous reports mainly focus on the application perspective, while a detailed characterization of the surface properties at the molecular level and the correlation with the synthesis conditions are missing. In this work, mesoporous TiO2 powder is grafted with 3-aminopropylphosphonic acid (3APPA) under different concentrations (20, 75, 150 mM) and temperatures (50, 90 °C) and compared with propylphosphonic acid (3PPA) grafting to unambiguously reveal the impact of the amine group on the surface properties. A combination of complementary spectroscopic techniques and Density Functional Theory -Periodic Boundary Conditions (DFT/PBC) calculations are used. At 90 °C and high concentrations, lower modification degrees are obtained for 3APPA compared to Revised manuscript (unmarked) ick ere t vie inked Re erences 2 3PPA, due to amine-induced surface interactions. Both X-ray Photoelectron Spectroscopy (XPS) and Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy reveal that both NH2 and NH3 + groups are present, with also contributions of NH2 groups involved in hydrogen bonding interactions. A similar ratio of NH2/NH3 + (65:35) is obtained irrespective of the modification conditions, suggesting similar relative contributions of different surface conformations. Calculated adsorption energies from DFT calculations on 3APPA adsorption on anatase (101) in relation to the water coverage reveals a coexistence of various structures with the amine group involved in intra-adsorbate, inter-adsorbate and adsorbate-surface interactions. Further validation is obtained from the strong overlap of different 31 P environments represented by the broad band (35-12 ppm) in experimental 31 P Nuclear Magnetic Resonance (NMR) spectra and calculated 31 P chemical shifts of all modelled monodentate and bidentate structures. Structures related to the tridentate binding mode are not formed due to geometric restrictions of the anatase (101) facet applied as model support in the calculations. Nevertheless, they could be present in the experimental samples as they are composed of anatase (representing multiple crystal facets) and an amorphous titania fraction.

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Phosphonic acid modifiers for enhancing selective hydrodeoxygenation over Pt catalysts: The role of the catalyst support

Cited by 27 publications

References 48 publications

Effects of Phosphonic Acid Monolayers on the Dehydration Mechanism of Aliphatic Alcohols on TiO₂

Effects of Phosphonic Acid Monolayers on the Dehydration Mechanism of Aliphatic Alcohols on TiO₂

Organic Modifiers Promote Furfuryl Alcohol Ring Hydrogenation via Surface Hydrogen-Bonding Interactions

Experimental and computational insights into the aminopropylphosphonic acid modification of mesoporous TiO2 powder: The role of the amine functionality on the surface interaction and coordination

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Phosphonic acid modifiers for enhancing selective hydrodeoxygenation over Pt catalysts: The role of the catalyst support

Cited by 27 publications

References 48 publications

Effects of Phosphonic Acid Monolayers on the Dehydration Mechanism of Aliphatic Alcohols on TiO2

Effects of Phosphonic Acid Monolayers on the Dehydration Mechanism of Aliphatic Alcohols on TiO2

Organic Modifiers Promote Furfuryl Alcohol Ring Hydrogenation via Surface Hydrogen-Bonding Interactions

Experimental and computational insights into the aminopropylphosphonic acid modification of mesoporous TiO2 powder: The role of the amine functionality on the surface interaction and coordination

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Effects of Phosphonic Acid Monolayers on the Dehydration Mechanism of Aliphatic Alcohols on TiO₂

Effects of Phosphonic Acid Monolayers on the Dehydration Mechanism of Aliphatic Alcohols on TiO₂