Distribution of Pt single atom coordination environments on anatase TiO2 supports controls reactivity

Single-atom catalysts (SACs) offer efficient metal utilization and distinct reactivity compared to supported metal nanoparticles. Structure-function relationships for SACs often assume that active sites have uniform coordination environments at particular binding sites on support surfaces. Here, we investigate the distribution of coordination environments of Pt SAs dispersed on shape-controlled anatase TiO2 supports specifically exposing (001) and (101) surfaces. Pt SAs on (101) are found on the surface, consistent with existing structural models, whereas those on (001) are beneath the surface after calcination. Pt SAs under (001) surfaces exhibit lower reactivity for CO oxidation than those on (101) surfaces due to their limited accessibility to gas phase species. Pt SAs deposited on commercial-TiO2 are found both at the surface and in the bulk, posing challenges to structure-function relationship development. This study highlights heterogeneity in SA coordination environments on oxide supports, emphasizing a previously overlooked consideration in the design of SACs.

Refocusing in Situ Electron Microscopy: Moving beyond Visualization of Nanoparticle Self-Assembly To Gain Practical Insights into Advanced Material Fabrication

Despite incredible progress in preparing extended nanoparticle superlattices by self-assembly, theoretically predicted collective properties of extended nanoparticle superlattices are rarely correlated to observations due to the presence of defects. Enhanced fundamental understanding of the kinetics involved in nanoparticle superlattice self-assembly, specifically defect formation and annealing kinetics and mechanisms, is needed to prepare defect-free nanoparticle superlattices. In situ transmission electron microscopy (TEM) enables direct visualization of nanoparticle self-assembly phenomena in real time and at atomic spatial resolution; however, effective translation of in situ TEM data into new predictive models and material synthesis design rules remains a persistent challenge. Recent work by Ondry et al. in this issue of ACS Nano utilized atomic resolution in situ TEM to establish defect removal kinetics in epitaxially attached CdSe nanocrystal pairs, revealing a set of practical guidelines for minimizing defect formation in extended nanoparticle solids. Motivated by this work, in this Perspective, I explore and discuss the most effective and impactful uses of in situ TEM for nanoscience research and the associated technical barriers for performing in situ TEM measurements that are meaningful to bulk-scale self-assembly experiments.

Perspectives on the design of nanoparticle systems for catalysis

An overview of the Faraday Discussion, "Designing Nanoparticle Systems for Catalysis", is presented. Examples are taken from the papers presented at the meeting and from the literature to illustrate the main discussion points.

Water Dissociation and Hydroxyl Ordering on Anatase TiO_{2}(001)-(1×4)

We studied the interaction of water with the anatase TiO_{2}(001) surface by means of scanning tunneling microscopy, x-ray photoelectron spectroscopy, and density functional theory calculations. Water adsorbs dissociatively on the ridges of a (1×4) reconstructed surface, resulting in a (3×4) periodic structure of hydroxyl pairs. We observed this process at 120 K, and the created hydroxyls desorb from the surface by recombination to water, which occurs below 300 K. Our calculations reveal the water dissociation mechanism and uncover a very pronounced dependence on the coverage. This strong coverage dependence is explained through water-induced reconstruction on anatase TiO_{2}(001)-(1×4). The high intrinsic reactivity of the anatase TiO_{2}(001) surface towards water observed here is fundamentally different from that seen on other surfaces of titania and may explain its high catalytic activity in heterogeneous catalysis and photocatalysis.