The preparation of silica supported, dilute limit PdAu alloys <i>via</i> simultaneous strong electrostatic adsorption

Dong, Anhua; Shakouri, Abolfazl; Karakalos, Stavros; Blom, Douglas A.; Williams, Christopher T.; Regalbuto, John R.

doi:10.1039/d2cy01662a

Cited by 3 publications

(2 citation statements)

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“…To complement the NP size analysis from TEM images, we acquired powder X-ray diffraction (XRD) data of the catalysts (Figure a). In all catalysts, broad reflection peaks matching the Au literature reference were recorded, characteristic of nanosized crystallites and verifying the dilute nature of Pd in the NP composition . The average crystallite size by Scherrer analysis of the Au (111) reflection peak was 6.2, 6.8, and 7.6 nm for x = 3.6, 4.5, and 5.0 nm, respectively, regardless of the sparse/dense nature of the catalysts (Table S1).…”

Section: Resultssupporting

confidence: 65%

“…In all catalysts, broad reflection peaks matching the Au literature reference were recorded, characteristic of nanosized crystallites and verifying the dilute nature of Pd in the NP composition. 49 The average crystallite size by Scherrer analysis 50 of the Au (111) reflection peak was 6.2, 6.8, and 7.6 nm for x = 3.6, 4.5, and 5.0 nm, respectively, regardless of the sparse/dense nature of the catalysts (Table S1). While the XRD-determined sizes were larger than the TEM-determined results, the trend in NP size, which is more important, is consistent between both methods.…”

Section: Resultsmentioning

confidence: 97%

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Deconvoluting the Individual Effects of Nanoparticle Proximity and Size in Thermocatalysis

Lim,

Kaiser,

et al. 2024

ACS Nano

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Nanoparticle (NP) size and proximity are two physical descriptors applicable to practically all NP-supported catalysts. However, with conventional catalyst design, independent variation of these descriptors to investigate their individual effects on thermocatalysis remains challenging. Using a raspberry-colloid-templating approach, we synthesized a well-defined catalyst series comprising Pd 12 Au 88 alloy NPs of three distinct sizes and at two different interparticle distances. We show that NP size and interparticle distance independently control activity and selectivity, respectively, in the hydrogenation of benzaldehyde to benzyl alcohol and toluene. Surface-sensitive spectroscopic analysis indicates that the surfaces of smaller NPs expose a greater fraction of reactive Pd dimers, compared to inactive Pd single atoms, thereby increasing intrinsic catalytic activity. Computational simulations reveal how a larger interparticle distance improves catalytic selectivity by diminishing the local benzyl alcohol concentration profile between NPs, thus suppressing its readsorption and consequently, undesired formation of toluene. Accordingly, benzyl alcohol yield is maximized using catalysts with smaller NPs separated by larger interparticle distances, overcoming activity−selectivity trade-offs. This work exemplifies the high suitability of the modular raspberrycolloid-templating method as a model catalyst platform to isolate individual descriptors and establish clear structure−property relationships, thereby bridging the materials gap between surface science and technical catalysts.

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Section: Resultssupporting

confidence: 65%

Section: Resultsmentioning

confidence: 97%

Deconvoluting the Individual Effects of Nanoparticle Proximity and Size in Thermocatalysis

Lim,

Kaiser,

et al. 2024

ACS Nano

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Metal Phthalocyanines Encapsulated in Faujasite Zeolites for Gas-Phase CO Oxidation

Iaia,

Rana,

Soyemi

et al. 2024

ACS Appl. Nano Mater.

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Existing metal-containing porous catalysts have inherent heterogeneity in metal species, rendering it difficult to compare reactivity across varied catalyst formulations without first developing active site quantification protocols. The supercages of faujasite zeolites (FAU) are large enough to confine metal phthalocyanines (MPCs), together serving as a well-defined active center for experimental and computational catalyst characterization. Deviations in zeolite synthesis conditions from prior literature were required to obtain phase-pure FAU. Metal perchloro-, perfluoro-, and perhydrogenated phthalocyanines (MPCCl16, MPCF16, and MPC; M = Cr, Mn, Fe, Co, Ni, Cu, and Zn) were encapsulated into FAU zeolites via hydrothermal synthesis (MPC@FAU) and deposited onto the external surfaces by postsynthetic deposition (MPC/FAU). These MPC@FAU catalysts were tested as catalysts for CO oxidation with dioxygen at 298 K and their reactivity compared to that of silica-supported PdAu nanoparticles and cobalt–nitrogen-doped carbon (Co–N–C). Initial CO2 site time yields were greater than the analogous metal-ion-exchanged zeolites (by ∼50×). However, this initial activity decreased with time on stream for all MPC samples tested, and the cause of this deactivation is explored herein. Stable CO2 formation rates with time on stream observed over PdAu/SiO2 and Co–N–C suggest that deactivation observed over MPC@FAU samples is distinct and not an artifact of the experimental apparatus. Density functional theory calculations suggest an O2-activation mechanism, aided by the coadsorption of CO on the pyrrole N of the MPC and an axial ligand that can provide additional electron density to reduce the barrier for O2 bond breaking; this reaction mechanism is distinct from that over structurally similar metal-nitrogen-doped carbons. Nevertheless, the reactivity of MPC@FAU catalysts for gas-phase CO oxidation with dioxygen at ambient temperature indicates that they may share similar functionality to metal–nitrogen-doped carbons and have the potential to serve as model catalysts for gas-phase chemistries.

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Impact of Particle Size on the Vapor-Phase Oxidative Coupling of Methanol and Dimethylamine over Palladium–Gold Nanoparticles

Minne,

Iaia,

Stavitski

et al. 2024

ACS Catal.

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Oxidative coupling of methanol and dimethylamine in the presence of O 2 in the vapor phase over dilute Pd in Au bimetallic catalysts occurs via the dissociation of O 2 on Pd and selective oxidation of methanol on Au. Here, we synthesize a series of silica-supported PdAu alloy nanoparticle catalysts of varied Pd:Au ratios with ∼5 nm particle diameter and show that these catalysts have increased selectivity to dimethylformamide across all Pd:Au ratios (∼95%), distinct from observations over larger PdAu nanoparticles (∼15−25 nm diameter) of similar Pd:Au ratios. Small monometallic Pd particles are more selective than large monometallic Pd particles, and small Au nanoparticles are reactive and selective for oxidative coupling (while large Au nanoparticles are inactive). Rates per surface metal atom were similar over PdAu nanoparticles of all sizes and increased monotonically with increasing Pd content for the small nanoparticles. Apparent reaction kinetics demonstrate distinct apparent methanol reaction order and apparent activation energy relative to those reported over larger nanoparticles of similar Pd:Au ratios. Unlike larger PdAu nanoparticles, the rate of dimethylformamide formation is not promoted by cofed water over small PdAu nanoparticles. The results of the kinetic studies are used to propose a series of elementary steps, derive a plausible rate expression, and regress rate and equilibrium constants. These results suggest high coverages of surface methoxy species and low coverages of adsorbates derived from dimethylamine. Taken together, these results demonstrate the sensitivity of the rates, selectivities, and kinetics of oxidative coupling reactions to the size of bimetallic nanoparticles.

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The preparation of silica supported, dilute limit PdAu alloys via simultaneous strong electrostatic adsorption

Abstract: Supported, dilute Pd-in-Au alloyed nanoparticles might possess enhanced reactivity due to the altered structural and electronic properties of the Pd atoms isolated in an Au nanoparticle matrix. Simultaneous strong electrostatic...

Cited by 3 publications

References 61 publications

Deconvoluting the Individual Effects of Nanoparticle Proximity and Size in Thermocatalysis

Deconvoluting the Individual Effects of Nanoparticle Proximity and Size in Thermocatalysis

Metal Phthalocyanines Encapsulated in Faujasite Zeolites for Gas-Phase CO Oxidation

Impact of Particle Size on the Vapor-Phase Oxidative Coupling of Methanol and Dimethylamine over Palladium–Gold Nanoparticles

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