Interparticle Heterogeneities Research Articles

In Situ Measurement of Nanoparticle-Blood Protein Adsorption and Its Heterogeneity with Single-Nanoparticle Resolution via Dual Fluorescence Quantification.

The formation of a protein corona gives nanomedicines a distinct biological identity, profoundly influencing their fate in the body. Nonspecific nanoparticle-protein interactions are typically highly heterogeneous, which can lead to unique biological behaviors and in vivo fates for individual nanoparticles that remain underexplored. To address this, we have established an in situ approach that allows quantitative examination of nanoparticle-protein adsorption at the individual nanoparticle level. This method integrates dual fluorescence quantification techniques, wherein the nanoparticles are first individually analyzed via nanoflow cytometry to detect fluorescent signals from adsorbed proteins. The obtained fluorescence intensity is then translated into protein quantities through calibration with microplate reader quantification. Consequently, this approach enables analysis of interparticle heterogeneity of nano-protein interactions, as well as in situ monitoring of protein adsorption kinetics and nanoparticle aggregation status in blood serum, preconditioning for a comprehensive understanding of nano-bio interactions, and predicting in vivo fate of nanomedicines.

Biomolecular interactions on densely coated nanoparticles: a single-molecule perspective.

DNA-modified gold nanoparticles (AuNPs) play a pivotal role in bio-nanotechnology, driving advancements in bio-sensing, bio-imaging, and drug delivery. Synthetic protocols have focused on maximizing the receptor density on particles by fine-tuning chemical conditions, particularly for DNA. Despite their significance, the understanding of hybridization kinetics on functionalized AuNPs is lacking, particularly how this kinetics depends on DNA density and to what extent it varies from particle-to-particle. This study explores the molecular mechanisms of DNA hybridization on densely coated AuNPs by employing a combination of single-molecule microscopy and coarse-grained molecular dynamics simulations providing a quantification of the molecular rate constants for single particles. Our findings demonstrate that DNA receptor density and the presence of spacer strands profoundly impact association kinetics, with short spacers enhancing association rates by up to ∼15-fold. In contrast, dissociation kinetics are largely unaffected by receptor density within the studied range. Single-particle analysis directly reveals variability in hybridization kinetics, which is analyzed in terms of intra- and inter-particle heterogeneity. A coarse-grained DNA model that quantifies hybridization kinetics on densely coated surfaces further corroborates our experimental results, additionally shedding light on how transient base pairing within the DNA coating influences kinetics. This integrated approach underscores the value of single-molecule studies and simulations for understanding DNA dynamics on densely coated nanoparticle surfaces, offering guidance for designing DNA-functionalized nanoparticles in sensor applications.

Imaging Voids and Defects Inside Li-Ion Cathode LiNi0.6Mn0.2Co0.2O2 Single Crystals.

Li-ion battery cathode active materials obtained from different sources or preparation methods often exhibit broadly divergent performance and stability despite no obvious differences in morphology, purity, and crystallinity. We show how state-of-the-art, commercial, nominally single crystalline LiNi0.6Mn0.2Co0.2O2 (NMC-622) particles possess extensive internal nanostructure even in the pristine state. Scanning X-ray diffraction microscopy reveals the presence of interlayer strain gradients, and crystal bending is attributed to oxygen vacancies. Phase contrast X-ray nano-tomography reveals two different kinds of particles, welded/aggregated, and single crystal like, and emphasizes the intra- and interparticle heterogeneities from the nano- to the microscale. It also detects within the imaging resolution (100 nm) substantial quantities of nanovoids hidden inside the bulk of two-thirds of the overall studied particles (around 3000), with an average value of 12.5%v per particle and a mean size of 148 nm. The powerful combination of both techniques helps prescreening and quantifying the defective nature of cathode material and thus anticipating their performance in electrode assembly/battery testing.

Engineering a tunable micropattern-array assay to sort single extracellular vesicles and particles to detect RNA and protein in situ.

The molecular heterogeneity of extracellular vesicles (EVs) and the co-isolation of physically similar particles, such as lipoproteins (LPs), confounds and limits the sensitivity of EV bulk biomarker characterization. Herein, we present a single-EV and particle (siEVP) protein and RNA assay (siEVP PRA) to simultaneously detect mRNAs, miRNAs, and proteins in subpopulations of EVs and LPs. The siEVP PRA immobilizes and sorts particles via positive immunoselection onto micropatterns and focuses biomolecular signals in situ. By detecting EVPs at a single-particle resolution, the siEVP PRA outperformed the sensitivities of bulk-analysis benchmark assays for RNA and protein. To assess the specificity of RNA detection in complex biofluids, EVs from various glioma cell lines were processed with small RNA sequencing, whereby two mRNAs and two miRNAs associated with glioblastoma multiforme (GBM) were chosen for cross-validation. Despite the presence of single-EV-LP co-isolates in serum, the siEVP PRA detected GBM-associated vesicular RNA profiles in GBM patient siEVPs. The siEVP PRA effectively examines intravesicular, intervesicular, and interparticle heterogeneity with diagnostic promise.

Getting the Most Out of Fluorogenic Probes: Challenges and Opportunities in Using Single-Molecule Fluorescence to Image Electro- and Photocatalysis.

Single-molecule fluorescence microscopy enables the direct observation of individual reaction events at the surface of a catalyst. It has become a powerful tool to image in real time both intra- and interparticle heterogeneity among different nanoscale catalyst particles. Single-molecule fluorescence microscopy of heterogeneous catalysts relies on the detection of chemically activated fluorogenic probes that are converted from a nonfluorescent state into a highly fluorescent state through a reaction mediated at the catalyst surface. This review article describes challenges and opportunities in using such fluorogenic probes as proxies to develop structure-activity relationships in nanoscale electrocatalysts and photocatalysts. We compare single-molecule fluorescence microscopy to other microscopies for imaging catalysis in situ to highlight the distinct advantages and limitations of this technique. We describe correlative imaging between super-resolution activity maps obtained from multiple fluorogenic probes to understand the chemical origins behind spatial variations in activity that are frequently observed for nanoscale catalysts. Fluorogenic probes, originally developed for biological imaging, are introduced that can detect products such as carbon monoxide, nitrite, and ammonia, which are generated by electro- and photocatalysts for fuel production and environmental remediation. We conclude by describing how single-molecule imaging can provide mechanistic insights for a broader scope of catalytic systems, such as single-atom catalysts.

Unveiling the role of electrode-level heterogeneity alleviated in a silicon-graphite electrode under operando microscopy

Reaction heterogeneity is a crucial factor that influences the design of composite electrodes. Silicon–graphite composites exhibit practical use as anodes, but the complex mechanisms in blended electrodes have not been investigated. Considering mechanisms at an electrode level, intra-/interparticle heterogeneity depending on state-of-charge (SOC) becomes problematic due to their complex kinetic properties. We investigate the complex dynamics of a silicon–graphite blended electrode using side-view operando optical microscopy, highlighting the proper mechanisms of SOC heterogeneity. Graphite and silicon simultaneously lithiated during lithiation by competition between redox potentials and interparticle diffusion. During delithiation, the driving force of electrochemical potentials increases, resulting in sequential reactions from graphite to silicon. Different kinetics induces interplay during the competitive reaction, affecting depth heterogeneity. Silicon mitigates the depth heterogeneity of graphite during lithiation due to its rapid surface diffusion and kinetic-derived overpotential. These findings pave new avenues for a more sophisticated design of high-energy Si-graphite anodes.

Mimicking industrial aging in fluid catalytic cracking: A correlative microscopy approach to unravel inter-particle heterogeneities

Artificially mimicking aging of an equilibrium catalyst (ECAT) is an effective strategy to model the deactivation of a Fluid Catalytic Cracking (FCC) catalyst during refinery operations. Herein, we have used a correlative microscopy approach to unravel inter-particle spatial heterogeneities in artificially deactivated catalysts (DCATs) and compared them with a real-life ECAT containing on average 3800 ppm of Ni and 2300 ppm of V, and a set of density separated ECAT fractions. By doing so we could rationalize the effect of metal contaminants on catalyst acidity and pore accessibility. More specifically, the Fe, Ni, and V distributions were obtained using X-Ray Fluorescence (XRF), while Confocal Fluorescence Microscopy (CFM) after thiophene and Nile Blue A staining, respectively provided a visualization of Brønsted acid sites and accessibility distribution. We found that not only the metal poisons distribution, but also hydrothermal degradation, that affects ECATs dealumination and related acidity drop, need to be properly reproduced by artificial catalyst deactivation protocols. Fe contamination must also be taken into account since it affects matrix accessibility.

Visualization of gaseous iodine adsorption on single zeolitic imidazolate framework-90 particles

Zeolitic imidazolate frameworks (ZIFs) are very useful as high-capacity iodine (I2) adsorbents. The adsorption performance is usually probed by measuring a statistical average property over an entire sample consisting of a large number of ZIF particles, leaving the interparticle heterogeneity information among individuals. Here we report a dark-field microscopy (DFM) method to visualize gaseous I2 adsorption on single ZIF-90 particles in situ and in real time. The adsorption of I2 is found to alter the scattering spectrum of ZIF-90 particles, inducing a distinct color change from bluewhite to yellow. According to correlating the adsorption amount of gaseous I2 with the change of B value from DFM images, we quantitatively image the adsorption process and estimate the related kinetic parameters at the single particle level. Single particle measurements clarify the large particle-to-particle heterogeneity in adsorption reactivity and significant adsorption activity improvement of ZIF-90 after introduction of linker defects, which provides a microscopic understanding of the structure-activity relationship. We further demonstrate the capacity of this strategy for studying gaseous I2 adsorption on single ZIF-91 particle as a derivative of ZIF-90 to illustrate the generality.

Lanthanide-Based Nanosensors: Refining Nanoparticle Responsiveness for Single Particle Imaging of Stimuli.

Lanthanide nanoparticles (LNPs) are promising sensors of chemical, mechanical, and temperature changes; they combine the narrow-spectral emission and long-lived excited states of individual lanthanide ions with the high spatial resolution and controlled energy transfer of nanocrystalline architectures. Despite considerable progress in optimizing LNP brightness and responsiveness for dynamic sensing, detection of stimuli with a spatial resolution approaching that of individual nanoparticles remains an outstanding challenge. Here, we highlight the existing capabilities and outstanding challenges of LNP sensors, en-route to nanometer-scale, single particle sensor resolution. First, we summarize LNP sensor read-outs, including changes in emission wavelength, lifetime, intensity, and spectral ratiometric values that arise from modified energy transfer networks within nanoparticles. Then, we describe the origins of LNP sensor imprecision, including sensitivity to competing conditions, interparticle heterogeneities, such as the concentration and distribution of dopant ions, and measurement noise. Motivated by these sources of signal variance, we describe synthesis characterization feedback loops to inform and improve sensor precision, and introduce noise-equivalent sensitivity as a figure of merit of LNP sensors. Finally, we project the magnitudes of chemical and pressure stimulus resolution achievable with single LNPs at nanoscale resolution. Our perspective provides a roadmap for translating ensemble LNP sensing capabilities to the single particle level, enabling nanometer-scale sensing in biology, medicine, and sustainability.

Single Particle Assays to Determine Heterogeneities within Fluid Catalytic Cracking Catalysts.

Fluid catalytic cracking (FCC) is an important process in oil refinery industry to produce gasoline and propylene. Due to harsh reaction conditions, FCC catalysts are subject to deactivation through for example, metal accumulation and zeolite framework collapse. Here, we perform a screening of the influence of metal poisons on the acidity and accessibility of an industrial FCC catalyst material using laboratory‐based single particle characterization that is, μ‐XRF and fluorescence microscopy in combination with probe molecules. These methods have been performed on density‐separated FCC catalyst fractions, allowing to determine interparticle heterogeneities in the catalyst under study. It was found that with increasing catalyst density and metal content, the acidity and accessibility of the catalyst particles decreased, while their distribution narrowed with catalyst age. For example, particles containing high Ni level possessed very low acidity and were hardly accessible by a Nile Blue dye. Single catalyst particle mapping identifies minority species like the presence of a phosphated zeolite ZSM‐5‐containing FCC additive for selective propylene formation, catalyst particles without any zeolite phase and catalyst particles, which act as a trap for SOx.

Long‐Term Storage and Age‐Biased Export of Fluvial Organic Carbon: Field Evidence From West Iceland

AbstractTerrestrial organic carbon (OC) plays an important role in the carbon cycle, but questions remain regarding the controls and timescale(s) over which atmospheric CO2 remains sequestered as particulate OC (POC). Motivated by observations that terrestrial POC is physically stored within soils and other shallow sedimentary deposits, we examined the role that sediment storage plays in the terrestrial OC cycle. Specifically, we tested the hypothesis that sediment storage impacts the age of terrestrial POC. We focused on the Efri Haukadalsá River catchment in Iceland as it lacks ancient sedimentary bedrock that would otherwise bias radiocarbon‐based determinations of POC storage duration by supplying pre‐aged “petrogenic” POC.Our radiocarbon measurements of riverine suspended sediments and deposits implicated millennial‐scale storage times. Comparison between the sample types (suspended and deposits) suggested an age offset between transported (suspended sediments) and stored (deposits) POC at the time of sampling, which is predicted by theory for the sediment age distribution in floodplains. We also observed that POC in suspended sediments is younger than the predicted mean storage duration generated from independent geomorphological data, which suggested an additional role for OC cycling. Consistent with this, we observed interparticle heterogeneity in the composition of POC by imaging our samples at the microscale using X‐ray absorption spectroscopy. Specifically, we found that particles within individual samples differed in their sulfur oxidation state, which is indicative of multiple origins and/or diagenetic histories. Altogether, our results support recent coupled sediment storage and OC cycling models and indicate that the physical drivers of sediment storage are important factors controlling the cadence of carbon cycling.

Heterogeneities of fly ash particles generated from a fluidized bed combustor of municipal solid waste incineration

Although municipal solid waste incineration fly ash are fine particles and a priori considered as homogeneous, they have complicated structures inside their bodies. This study quantitatively investigated two categories of heterogeneity of fly ash produced from a fluidized bed combustor. They are the heterogeneity of a single fly ash particle body (intra-particle heterogeneity) and heterogeneity among fly ash particles (inter-particle heterogeneity). In the surface and semi-soluble components, Ca has smaller intra-particle heterogeneity than Al and Si. These results and ternary diagram analysis suggest that semi-soluble components consisted of mainly Ca-based matrices such as CaCO3 and unreacted Ca(OH)2 in which aluminosilicate domains. All major elements, excluding Fe and Ti, are 3–66% higher inter-particle heterogeneities on the surface than semi-soluble and insoluble core components. It shows that the surface component of the fly ash is more heterogeneous than other components of fly ash particles. Fly ash from fluidized bed combustor has intra- and inter-particle heterogeneity similar to stoker combustor. Besides, heterogeneity analysis can explain the fly ash formation process. Heterogeneity analysis suggests that Si plays more critical roles in the fly ash formation process of the fluidized bed combustor than that of the stoker combustor. Fly ash has heterogeneous bodies, and it might give non-negligible impacts on the leaching of metals included in fly ash components.

Electrodissolution Inhibition of Gold Nanorods with Oxoanions

The incorporation of metal nanoparticles into bulk electrochemical systems has resulted in technological advances in electronics, electrocatalysis, and sensing. Metal “nanoelectrodes” are exposed to varied chemical environments that can cause dissolution under applied potentials, often below bulk oxidation values. Gold nanorods are being developed as superior light harvesting nanoantennas in photoelectrocatalysis, and light scatterers for nanoscopic spectroelectrochemical sensing. However, dissolution poses a critical problem for gold nanoelectrode functionalized devices as the electrochemical and optical properties of nanoparticles are highly dependent on size and shape, and the cost of replacement can be prohibitive. We employed an analytical, single particle approach to monitor the chloride-mediated dissolution pathway of gold nanorods in the presence of oxoanion electrodissolution inhibitors. Hyperspectral dark-field imaging revealed that the morphological stability of gold nanorods at anodic potentials improved with the addition of low relative concentrations of oxoanions to aqueous halide electrolyte solutions. Single particle measurements were necessary to address the inter-particle heterogeneity of chemically synthesized gold nanorods. Direct correlation imaging of single gold nanorods with scanning electron microscopy supported the reaction pathway heterogeneity statistics and electrodissolution potentials obtained spectroscopically. We determined that the electrodissolution inhibition capacity of oxoanions in the presence of chloride ions for gold nanoparticles was governed primarily by the electroadsorption potential and ionicity of the oxoanion. Determining the factors for inhibition will assist in the expansion of the electrochemical stability window, opening new avenues for gold nanoelectrodes in diverse and harsh catalytic and sensing environments.

Intra- and inter-particle heterogeneity of municipal solid waste incineration fly ash particles

This study firstly investigated elemental heterogeneity of municipal solid waste incineration (MSWI) fly ash particles. Two types of heterogeneities were measured quantitatively focusing on three structural components of fly ash particles. They are internal heterogeneity of individual fly ash particles (intra-particle heterogeneity) and inter-particle heterogeneities among fly ash particles. On the surface of fly ash particles, Cl, K, and Na have 0–82% larger intra-particle heterogeneities than Al, Ca, and Si owing to KCl/NaCl-based aggregates. Smaller intra-particle heterogeneity of Ca in semi-soluble component than those of Al and Si suggest that semi-soluble Al/Ca/Si-based matrices around insoluble cores are Ca-based materials including aluminosilicate domains. Inter-particle heterogeneities of Al, Ca, and Si in semi-soluble and insoluble components are 9–40% and 49–352% higher than those of fly ash particle surface, respectively. Inter-particle heterogeneity analysis also suggests that insoluble components mainly consists of Si-, Al-, or Ca-rich cores. MSWI fly ash particles have both internal heterogeneities inside their bodies and also are heterogeneous in inter-particle level. When MSWI fly ash becomes wet during chelate treatment, it changed intra-particle heterogeneity as well as inter-particle heterogeneity. Their variations were contrast depending on element and site (fly ash particle component).

Cover Feature: Intra‐ and Interparticle Heterogeneities in Solid Activators for Single‐Site Olefin Polymerization Catalysis as Revealed by Micro‐Spectroscopy (Chem. Eur. J. 46/2018)

Cover Feature: Intra‐ and Interparticle Heterogeneities in Solid Activators for Single‐Site Olefin Polymerization Catalysis as Revealed by Micro‐Spectroscopy (Chem. Eur. J. 46/2018)

Magnetophoretic Sorting of Single Catalyst Particles.

A better understanding of the deactivation processes taking place within solid catalysts is vital to design better ones. However, since inter-particle heterogeneities are more a rule than an exception, particle sorting is crucial to analyse single catalyst particles in detail. Microfluidics offers new possibilities to sort catalysts at the single particle level. Herein, we report a first-of-its-kind 3D printed magnetophoretic chip able to sort catalyst particles by their magnetic moment. Fluid catalytic cracking (FCC) particles were separated based on their Fe content. Magnetophoretic sorting shows that large Fe aggregates exist within 20 % of the FCC particles with the highest Fe content. The availability of Brønsted acid sites decreases with increasing Fe content. This work paves the way towards a high-throughput catalyst diagnostics platform to determine why specific catalyst particles perform better than others.

Intra‐ and Interparticle Heterogeneities in Solid Activators for Single‐Site Olefin Polymerization Catalysis as Revealed by Micro‐Spectroscopy

Methylaluminoxane (MAO) is an activator for single‐site olefin polymerization catalysts. Structural characterization of MAO, and in particular the influence of its heterogenization on a silica support, is pivotal for the understanding and optimization of this versatile co‐catalyst. In this work, we demonstrate that by varying the MAO loading on a silica support, we can tune the single particle characteristics in terms of MAO distribution and consequent activity. At low MAO loading we reveal two possible intraparticle MAO distributions: a homogeneous and an Al‐shell type distribution. With increasing MAO loading, the interparticle MAO distribution becomes more homogeneous. Acidity probing measurements on the single particle level explain how a different intraparticle MAO distribution results in a different activity in metallocene activation. Al‐shell particles contain remaining silanol groups and a negligible amount of acid sites and are, therefore, considered inactive for metallocene activation. Only the solid activator particles with a homogeneous intraparticle MAO distribution contain a sufficient number of acid sites, capable of activating the deposited metallocenes.

Origin and Abatement of Heterogeneity at the Support Granule Scale of Silver on Silica Catalysts

AbstractIncipient wetness impregnation is used commonly to form supported metal nanoparticle catalysts. Recently, it has been revealed that this approach may induce severe heterogeneity between catalyst granules of the same batch. At least a 10‐fold variation in metal loading was observed, which affect the catalytic performance of individual catalyst granules severely. However, the origin of this heterogeneity is still unclear. Here we show that every elementary step in the preparation procedure of a Ag on silica catalyst has an effect on the resulting interparticle heterogeneity, but the influence of the drying step is the most important. This is because drying by capillary force results in a heterogeneous sample. Specifically, the position of a granule in the stagnant drying bed influences the resulting color and, thus, Ag loading significantly. This is further demonstrated by varying the drying conditions: freeze‐drying and fluidized‐bed drying led to a more homogeneous Ag loading. An investigation of the fluidized‐bed‐dried sample by using optical microscopy revealed a large fraction of transparent granules (94 %), which indicates that almost all the Ag nanoparticles in this sample are confined within the 6 nm pores. The optimized supported Ag on silica catalyst shows a good catalytic performance. This adaptation of the drying step can be implemented easily on a laboratory scale, is scalable, and does not require the use of expensive solvents or metal precursors.

Resolving Interparticle Heterogeneities in Composition and Hydrogenation Performance between Individual Supported Silver on Silica Catalysts.

Supported metal nanoparticle catalysts are commonly obtained through deposition of metal precursors onto the support using incipient wetness impregnation. Typically, empirical relations between metal nanoparticle structure and catalytic performance are inferred from ensemble averaged data in combination with high-resolution electron microscopy. This approach clearly underestimates the importance of heterogeneities present in a supported metal catalyst batch. Here we show for the first time how incipient wetness impregnation leads to 10-fold variations in silver loading between individual submillimeter-sized silica support granules. This heterogeneity has a profound impact on the catalytic performance, with 100-fold variations in hydrogenation performance at the same level. In a straightforward fashion, optical microscopy interlinks single support particle level catalytic measurements to structural and compositional information. These detailed correlations reveal the optimal silver loading. A thorough consideration of catalyst heterogeneity and the impact thereof on the catalytic performance is indispensable in the development of catalysts.

CO Adsorption on Platinum Nanoparticles - the Importance of Size Distribution Studied with in-Situ DRIFTS and DFT Calculations

Catalyst degradation due to carbon support corrosion is a key issue in fuel cell technology. One concept towards enhanced durability is to replace carbon by more stable support materials such as oxides.1 However, this can alter the catalytic acitvity dramatically due to particle-support interaction. The particle-support interaction can be tested with the adsorption of small molecules such as CO. Differences in IR spectra of CO adsorption on platinum nanoparticles can reveal information on the influence of the support as well as on the binding sites. As a model system, we study the temperature dependence of CO adsorption on Pt/SiO2 with a combination of in-situ DRIFTS (Diffuse Reflectance Infrared Fourier Transform Spectroscopy) and DFT calculations to clarify the binding mode and to distinguish between interparticle and intraparticle heterogeneity. The concept of intraparticle heterogeneity implies that CO can be absorbed at different sites (facets, edges and corners) on a nanoparticle of a specific size2-4 whereas interparticle heterogeneity focuses on the adsorption on different nanoparticle sizes.5 CO adsorption was studied in the gas phase between 25°C - 175°C. The CO concentration as well as the pretreatment conditions were varied. Results for the reduced sample under 1% CO are shown in Fig. 1. For the DRIFTS data the corresponding temperature dependent background as well as the spectra without CO were carefully subtracted. Fig. 1 a-b) displays the measurements and their fits under constant CO flow, data in Fig 1 c-d) is taken after purging with nitrogen to remove excess CO and to test the thermal stability of the adsorbates. In all experiments, almost no bridge bonded CO is detected. The data can be fitted with three bands for linearly bonded CO at 25°C: band 1 at 2080 cm-1, band 2 at 2070 cm-1, and band 3 at 2050 cm-1. The DFT calculations show that the experimentally-observed differences in CO band positions are due to the interparticle heterogeneity, but not due to the intraparticle heterogeneity. We find that band 1 corresponds to CO adsorption on 1.8 nm Pt nanoparticles with a binding energy of 2.00 eV, while band 2 and 3 correspond to CO adsorption on ~1.5 nm (2.1 eV) and ~1.1 nm (2.3 eV), respectively. Under constant CO flow (Fig. 1 a-b)) the intensities of the fitted bands are highest for the most abundant nanoparticles of 1.8 nm.6 Desorption of CO molecules from larger nanoparticles (weaker binding energies) already starts at low temperatures (Fig. 1 c-d)). For temperatures higher than 100°C, CO molecules are only absorbed on the smaller nanoparticles (stronger binding energies). Our results show that nanoparticle size distribution (interparticle heterogeneity) has to be considered for adsorption studies on catalysts. The temperature dependence of CO adsorption on different cluster sizes could be used to identify reactive sites and thus are important for electrochemical activity and mechanistic studies. In future, these results will be coupled with in-situ XAS experiments and an electrochemical environment.