Scott Docherty

Last Name

Docherty

First Name

Scott

ORCID

0000-0002-8605-3669

Show all metadata

Search Results

Publications 1 - 10 of 17

Origin of Reactivity Trends of an Elusive Metathesis Intermediate from NMR Chemical Shift Analysis of Surrogate Analogues
Kakiuchi, Yuya; Docherty, Scott; Berkson, Zachariah J.; et al. (2024)
Journal of the American Chemical Society
Olefin metathesis has become an efficient tool in synthetic organic chemistry to build carbon-carbon bonds, thanks to the development of Grubbs- and Schrock-type catalysts. Olefin coordination, a key and often rate-determining elementary step for d0 Schrock-type catalysts, has been rarely explored due to the lack of accessible relevant molecular analogues. Herein, we present a fully characterized surrogate of this key olefin-coordination intermediate, namely, a cationic d0 tungsten oxo-methylidene complex bearing two N-heterocyclic carbene ligands─[WO(CH2)Cl(IMes)2](OTf) (1) (IMes = 1,3-dimesitylimidazole-2-ylidene, OTf-triflate counteranion), resulting in a trigonal bipyramidal (TBP) geometry, along with its neutral octahedral analogue [WO(CH2)Cl2(IMes)2] (2)─and an isostructural oxo-methylidyne derivative [WO(CH)Cl(IMes)2] (3). The analysis of their solid-state 13C and 183W MAS NMR signatures, along with computed 17O NMR parameters, helps to correlate their electronic structures with NMR patterns and evidences the importance of the competition among the three equatorial ligands in the TBP complexes. Anchored on experimentally obtained NMR parameters for 1, computational analysis of a series of olefin coordination intermediates highlights the interplay between σ- and π-donating ligands in modulating their stability and further paralleling their reactivity. NMR spectroscopy descriptors reveal the origin for the advantage of the dissymmetry in σ-donating abilities of ancillary ligands in Schrock-type catalysts: weak σ-donors avoid the orbital-competition with the oxo ligand upon formation of a TBP olefin-coordination intermediate, while stronger σ-donors compromise M≡O triple bonding and thus render olefin coordination step energy demanding.
Heterogeneous alkane dehydrogenation catalysts investigated via a surface organometallic chemistry approach
Docherty, Scott; Rochlitz, Lukas; Payard, Pierre-Adrien; et al. (2021)
Chemical Society Reviews
The selective conversion of light alkanes (C2–C6 saturated hydrocarbons) to the corresponding alkene is an appealing strategy for the petrochemical industry in view of the availability of these feedstocks, in particular with the emergence of Shale gas. Here, we present a review of model dehydrogenation catalysts of light alkanes prepared via surface organometallic chemistry (SOMC). A specific focus of this review is the use of molecular strategies for the deconvolution of complex heterogeneous materials that are proficient in enabling dehydrogenation reactions. The challenges associated with the proposed reactions are highlighted, as well as overriding themes that can be ascertained from the systematic study of these challenging reactions using model SOMC catalysts.
Gallium: A Universal Promoter Switching CO2 Methanation Catalysts to Produce Methanol
Zhou, Wei; Hansen, Colin; Cao, Weicheng; et al. (2025)
JACS Au
Hydrogenation of CO2 to methanol is foreseen as a key step to close the carbon cycle. In this study, we show that introducing Ga into silica-supported nanoparticles based on group 8-9 transition noble metals (M = Ru, Os, Rh, and Ir - MGa@SiO2) switches their reactivity from producing mostly methane (sel. > 97%) to producing methanol (>50% CH3OH/DME sel.) alongside CO as the only byproduct. These silica-supported catalysts, prepared via a surface organometallic chemistry (SOMC) approach, consist of small, alloyed, and narrowly distributed MGa nanoparticles, as evidenced by X-ray absorption spectroscopy (XAS) and CO adsorption studies. Notably, detailed in situ XAS and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) studies complemented with density functional theory (DFT) calculations indicate that Ga generates stable bulk MGa alloys. The bulk MGa alloys persist during CO2 hydrogenation according to XAS, resulting in suppressed methanation. Meanwhile, a small fraction of surface GaOx and thereby MGa-GaOx interfaces are formed, as evidenced by IR spectroscopy, likely responsible for stabilizing methoxy intermediates and favoring methanol formation.
$^2$H Quadrupolar Coupling Constant: A Spectroscopic Ruler for Transition Metal-Hydride Bond Distances in Molecular and Surface Sites
Gioffrè, Domenico; Müller, Cäcilie; Docherty, Scott; et al. (2025)
Journal of the American Chemical Society
Transition metal hydrides (TMHs) find numerous applications across fields from catalysis to H$_2$ storage. Yet, determining the structure of TMHs can remain a challenge, as hydrogen is difficult to detect by X-ray based or classical spectroscopic techniques. Considering that the deuterium isotope (D) is a quadrupolar nucleus (I = 1) and that a quadrupolar coupling constant (C$_Q$) depends on the distance between D and its bonding partner E (d$_{ED}$), we evaluate this trend across molecularly defined transition metal deuterides (TMDs) through a systematic investigation across TM block elements using both computations and experiments. We show that the M-D bond distance (d$_{MD}$) in [$\mathring{A}$] correlates with the C$_Q$ values in [kHz] as d$_{MD}$ = 7.83(C$_Q$ + 28.7)$^{-1/3}$ - independently from the nature of the TM - with an accuracy >0.04-0.08 $\mathring{A}$. Based on experimental C$_Q$ values measured by $^2$H solid-state NMR, this simple correlation is then used to obtain the M-D bond distances in two silica-supported TMDs (M = Zr and Ir), notable heterogeneous catalysts representing early and late TMDs, where evaluating M-D bond distances by other means is very challenging. Considering the ease of measurement, this method is readily applicable to a large range of diamagnetic terminal M-Ds, from molecular to surface sites, making $^2$H NMR a method of choice to measure TMD bond distances.
Selective Oxidation of Methane to Methanol over Au/H-MOR
Wang, Wangyang; Zhou, Wei; Tang, Yuchen; et al. (2023)
Journal of the American Chemical Society
Selectiveoxidation of methane to methanol by dioxygen (O-2) is anappealing route for upgrading abundant methane resource andrepresents one of the most challenging reactions in chemistry dueto the overwhelmingly higher reactivity of the product (methanol)versus the reactant (methane). Here, we report that gold nanoparticlesdispersed on mordenite efficiently catalyze the selective oxidationof methane to methanol by molecular oxygen in aqueous medium in thepresence of carbon monoxide. The methanol productivity reaches 1300 mu mol g(cat) (-1) h(-1) or 280 mmol g(Au) (-1) h(-1) with 75% selectivity at 150 degrees C, outperforming most catalystsreported under comparable conditions. Both hydroxyl radicals and hydroperoxidespecies participate in the activation and conversion of methane, whileit is shown that the lower affinity of methanol on gold mainly accountsfor higher methanol selectivity.
From ethene to propene (ETP) on tailored silica-alumina supports with isolated Ni(ii) sites: uncovering the importance of surface nickel aluminate sites and the carbon-pool mechanism
Chen, Zixuan; Docherty, Scott; Florian, Pierre; et al. (2022)
Catalysis Science & Technology
Catalysts with well-defined isolated Ni(ii) surface sites have been prepared on three silica-based supports. The outer shells of the support were comprised either of an amorphous aluminosilicate or amorphous alumina (AlOx) layer - associated with a high and low density of strong Bronsted acid sites (BAS), respectively. When tested for ethene-to-propene conversion, Ni catalysts with a higher density of strong BAS demonstrate a higher initial activity and productivity to propene. On all three catalysts, the propene productivity correlates closely with the concentration of C-8 aromatics, suggesting that propene may form via a carbon-pool mechanism. While all three catalysts deactivate with time on stream, the deactivation of catalysts with Ni(ii) sites on AlOx, i.e., containing surface Ni aluminate sites, is shown to be reversible by calcination (coke removal), in contrast to the deactivation of surface Ni silicate or aluminosilicate sites, which deactivate irreversibly by forming Ni nanoparticles.
Silica-Supported PdGa Nanoparticles: Metal Synergy for Highly Active and Selective CO2-to-CH3OH Hydrogenation
Docherty, Scott; Phongprueksathat, Nat; Lam, Erwin; et al. (2021)
JACS Au
The direct conversion of CO2 to CH3OH represents an appealing strategy for the mitigation of anthropogenic CO2 emissions. Here, we report that small, narrowly distributed alloyed PdGa nanoparticles, prepared via surface organometallic chemistry from silica-supported GaIII isolated sites, selectively catalyze the hydrogenation of CO2 to CH3OH. At 230 °C and 25 bar, high activity (22.3 molMeOH molPd–1 h–1) and selectivity for CH3OH/DME (81%) are observed, while the corresponding silica-supported Pd nanoparticles show low activity and selectivity. X-ray absorption spectroscopy (XAS), IR, NMR, and scanning transmission electron microscopy–energy-dispersive X-ray provide evidence for alloying in the as-synthesized material. In situ XAS reveals that there is a dynamic dealloying/realloying process, through Ga redox, while operando diffuse reflectance infrared Fourier transform spectroscopy demonstrates that, while both methoxy and formate species are observed in reaction conditions, the relative concentrations are inversely proportional, as the chemical potential of the gas phase is modulated. High CH3OH selectivities, across a broad range of conversions, are observed, showing that CO formation is suppressed for this catalyst, in contrast to reported Pd catalysts.
CO2 Hydrogenation to CH3OH on Supported Cu Nanoparticles: Nature and Role of Ti in Bulk Oxides vs Isolated Surface Sites
Noh, Gina; Docherty, Scott; Lam, Erwin; et al. (2019)
The Journal of Physical Chemistry C
Ethylene-to-propene (ETP) conversion over Ni(II) single sites on tailored silica-alumina supports
Chen, Zixuan; Docherty, Scott; Copéret, Christophe; et al. (2022)
Online Abstracts: 27th North American Catalysis Society Meeting
Application of the ALD of TMA onto dehydroxylated silica allows the precise control of the abundance of strong BAS on the support. The abundance of strong BAS is found to correlate directly with the ETP activity of Ni(II) single sites supported on such ALD-prepared silica-aluminates.
Surface Intermediates in In-Based ZrO2-Supported Catalysts for Hydrogenation of CO2 to Methanol
Tsoukalou, Athanasia; Bushkov, Nikolai S.; Docherty, Scott; et al. (2022)
The Journal of Physical Chemistry C
The influence of the phase of the ZrO2 support (monoclinic, tetragonal, and amorphous, referred to as m-, t-, and am-, respectively) on the nature of the surface species involved in methanol synthesis and the rates of their formation on ZrO2-supported, In-based catalysts for CO2 hydrogenation has been investigated. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) at 300 degrees C and 20 bar (H-2:CO2:N-2 = 3:1:1 volume ratio) on m-ZrO2:In, In2O3/t-ZrO2, and In2O3/am-ZrO2 catalysts (m-ZrO2:In is a solid solution) shows that formate species (HCOO*) appear prior to methoxy species (*OCH3), and both intermediates form faster on the more active m- ZrO2:In catalyst. Only formate bands are detected for the In2O3/t-ZrO2 catalyst. For these materials, indium sites are essential for the formation of HCOO* and *OCH3 species as only carbonate species are observed on m-, t-, and am-ZrO2 supports under CO2 hydrogenation conditions. The nature of the reaction intermediates is confirmed by ex situ solid-state nuclear magnetic resonance (NMR), where both methoxy and formate species are detected in m-ZrO2:In and In2O3/am-ZrO2, respectively, but only a weak formate peak is observed for In2O3/t-ZrO2. The presence of a major methoxy peak and only a very minor formate signal in unsupported In2O3 indicates that an india-zirconia interface is required for the effective stabilization of formate species. Catalytic tests in a fixed bed reactor are consistent with both CO and Me0H being primary products of CO2 hydrogenation; the tests also show that the methanol selectivity and space time yield decrease in the following order: m-ZrO2:In > In2O3/t-ZrO2 > In2O3/am-ZrO2 for all of the contact times tested.

Publications 1 - 10 of 17

Scott Docherty

Last Name

First Name

ORCID

Organisational unit

Filters

Search Results