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1. Partial PdAu nanoparticle embedding into TiO ₂ support accentuates catalytic contributions from the Au/TiO ₂ interface

   https://doi.org/10.1073/pnas.2422628122  

   Lim, Kang_Rui Garrick; Kaiser, Selina K; Herring, Connor J; Kim, Taek-Seung; Perich, Marta Perxés; Garg, Sadhya; O’Connor, Christopher R; Aizenberg, Michael; van_der_Hoeven, Jessi_E S; Reece, Christian; et al (January 2025, Proceedings of the National Academy of Sciences)

   Despite the broad catalytic relevance of metal–support interfaces, controlling their chemical nature, the interfacial contact perimeter (exposed to reactants), and consequently, their contributions to overall catalytic reactivity, remains challenging, as the nanoparticle and support characteristics are interdependent when catalysts are prepared by impregnation. Here, we decoupled both characteristics by using a raspberry-colloid-templating strategy that yields partially embedded PdAu nanoparticles within well-defined SiO₂or TiO₂supports, thereby increasing the metal–support interfacial contact compared to nonembedded catalysts that we prepared by attaching the same nanoparticles onto support surfaces. Between nonembedded PdAu/SiO₂and PdAu/TiO₂, we identified a support effect resulting in a 1.4-fold higher activity of PdAu/TiO₂than PdAu/SiO₂for benzaldehyde hydrogenation. Notably, partial nanoparticle embedding in the TiO₂raspberry-colloid-templated support increased the metal–support interfacial perimeter and consequently, the number of Au/TiO₂interfacial sites by 5.4-fold, which further enhanced the activity of PdAu/TiO₂by an additional 4.1-fold. Theoretical calculations and in situ surface-sensitive desorption analyses reveal facile benzaldehyde binding at the Au/TiO₂interface and at Pd ensembles on the nanoparticle surface, explaining the connection between the number of Au/TiO₂interfacial sites (via the metal–support interfacial perimeter) and catalytic activity. Our results demonstrate partial nanoparticle embedding as a synthetic strategy to produce thermocatalytically stable catalysts and increase the number of catalytically active Au/TiO₂interfacial sites to augment catalytic contributions arising from metal–support interfaces. 

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2. Functional CeOx nanoglues for efficient and robust atomically dispersed catalysts

   Li X, Hernandez XIP (June 2021, Research square)

   null (Ed.)

   Single-atom catalysts (SACs) exhibit unique catalytic property and maximum atom efficiency of rare, expensive metals. A critical barrier to applications of SACs is sintering of active metal atoms under operating conditions. Anchoring metal atoms onto oxide supports via strong metal-support bonds may alleviate sintering. Such an approach, however, usually comes at a cost: stabilization results from passivation of metal sites by excessive oxygen ligation—too many open coordination sites taken up by the support, too few left for catalytic action. Furthermore, when such stabilized metal atoms are activated by reduction at elevated temperatures they become unlinked and so move and sinter, leading to loss of catalytic function. We report a new strategy, confining atomically dispersed metal atoms onto functional oxide nanoclusters (denoted as nanoglues) that are isolated and immobilized on a robust, high-surface-area support—so that metal atoms do not sinter under conditions of catalyst activation and/or operation. High-number-density, ultra-small and defective CeOx nanoclusters were grafted onto high-surface-area SiO2 as nanoglues to host atomically dispersed Pt. The Pt atoms remained on the CeOx nanoglue islands under both O2 and H2 environment at high temperatures. Activation of CeOx supported Pt atoms increased the turnover frequency for CO oxidation by 150 times. The exceptional stability under reductive conditions is attributed to the much stronger affinity of Pt atoms for CeOx than for SiO2—the Pt atoms can move but they are confined to their respective nanoglue islands, preventing formation of larger Pt particles. The strategy of using functional nanoglues to confine atomically dispersed metal atoms and simultaneously enhance catalytic performance of localized metal atoms is general and takes SACs one major step closer to practical applications as robust catalysts for a wide range of catalytic transformations. 

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3. Active Sites of Cobalt Phthalocyanine in Electrocatalytic CO ₂ Reduction to Methanol

   https://doi.org/10.1002/anie.202310623  

   Rooney, Conor L; Lyons, Mason; Wu, Yueshen; Hu, Gongfang; Wang, Maoyu; Choi, Chungseok; Gao, Yuanzuo; Chang, Chun‐Wai; Brudvig, Gary W; Feng, Zhenxing; et al (January 2024, Angewandte Chemie International Edition)

   Abstract Many metal coordination compounds catalyze CO₂electroreduction to CO, but cobalt phthalocyanine hybridized with conductive carbon such as carbon nanotubes is currently the only one that can generate methanol. The underlying structure–reactivity correlation and reaction mechanism desperately demand elucidation. Here we report the first in situ X‐ray absorption spectroscopy characterization, combined with ex situ spectroscopic and electrocatalytic measurements, to study CoPc‐catalyzed CO₂reduction to methanol. Molecular dispersion of CoPc on CNT surfaces, as evidenced by the observed electronic interaction between the two, is crucial to fast electron transfer to the active sites and multi‐electron CO₂reduction. CO, the key intermediate in the CO₂‐to‐methanol pathway, is found to be labile on the active site, which necessitates a high local concentration in the microenvironment to compete with CO₂for active sites and promote methanol production. A comparison of the electrocatalytic performance of structurally related porphyrins indicates that the bridging aza‐N atoms of the Pc macrocycle are critical components of the CoPc active site that produces methanol. In situ X‐ray absorption spectroscopy identifies the active site as Co(I) and supports an increasingly non‐centrosymmetric Co coordination environment at negative applied potential, likely due to the formation of a Co−CO adduct during the catalysis. 

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4. A General Approach for Metal Nanoparticle Encapsulation Within Porous Oxides

   https://doi.org/10.1002/adma.202409710  

   Zhou, Chengshuang; Oh, Jinwon; Stone, Michael L; Richardson, Sydney; Chung, Pin‐Hung; Osio‐Norgaard, Jorge; Nhan, Bang T; Kumar, Abinash; Chi, Miaofang; Cargnello, Matteo (November 2024, Advanced Materials)

   Abstract Encapsulation of metal nanoparticles within oxide materials has been shown as an effective strategy to improve activity, selectivity, and stability in several catalytic applications. Several approaches have been proposed to encapsulate nanoparticles, such as forming core‐shell structures, growing ordered structures (zeolites or metal‐organic frameworks) on nanoparticles, or directly depositing support materials on nanoparticles. Here, a general nanocasting method is demonstrated that can produce diverse encapsulated metal@oxide structures with different compositions (Pt, Pd, Rh) and multiple types of oxides (Al₂O₃, Al₂O₃‐CeO₂, ZrO₂, ZnZrO_x, In₂O₃, Mn₂O₃, TiO₂) while controlling the size and dispersion of nanoparticles and the porous structure of the oxide. Metal@polymer structures are first prepared, and then the oxide precursor is infiltrated into such structures and the resulting material is calcined to form the metal@oxide structures. Most Pt@oxides catalysts show similar catalytic activity, demonstrating the availability of surface Pt sites in the encapsulated structures. However, the Pt@Mn₂O₃sample showed much higher CO oxidation activity, while also being stable under aging conditions. This work demonstrated a robust nanocasting method to synthesize metal@oxide structures, which can be utilized in catalysis to finely tune metal‐oxide interfaces. 

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5. Interpretable design of Ir-free trimetallic electrocatalysts for ammonia oxidation with graph neural networks

   https://doi.org/10.1038/s41467-023-36322-5  

   Pillai, Hemanth Somarajan; Li, Yi; Wang, Shih-Han; Omidvar, Noushin; Mu, Qingmin; Achenie, Luke E.; Abild-Pedersen, Frank; Yang, Juan; Wu, Gang; Xin, Hongliang (December 2023, Nature Communications)

   Abstract The electrochemical ammonia oxidation to dinitrogen as a means for energy and environmental applications is a key technology toward the realization of a sustainable nitrogen cycle. The state-of-the-art metal catalysts including Pt and its bimetallics with Ir show promising activity, albeit suffering from high overpotentials for appreciable current densities and the soaring price of precious metals. Herein, the immense design space of ternary Pt alloy nanostructures is explored by graph neural networks trained on ab initio data for concurrently predicting site reactivity, surface stability, and catalyst synthesizability descriptors. Among a few Ir-free candidates that emerge from the active learning workflow, Pt₃Ru-M (M: Fe, Co, or Ni) alloys were successfully synthesized and experimentally verified to be more active toward ammonia oxidation than Pt, Pt₃Ir, and Pt₃Ru. More importantly, feature attribution analyses using the machine-learned representation of site motifs provide fundamental insights into chemical bonding at metal surfaces and shed light on design strategies for high-performance catalytic systems beyond thed-band center metric of binding sites. 

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