Search

Palladium catalysts are highly efficient for a variety of chemical industrial processes but are prone to being affected by poisons during practical application. Sulfur is one of the major poisons in Pd-based catalysts. The recycling of deeply poisoned Pd species like Pd sulfides is challenging due to the strong Pd-S bond. Herein, we proposed a top-down strategy to degrade Pd sulfides and create Pd single-atom sites simultaneously by one-step thermal atomization. Pd 4 S model nanoparticles were successfully converted to Pd single-atom sites supported on nitrogen and sulfur-codoped carbon (Pd 1 /N, S-C) after loading them on ZIF-8 and thermal treatment. PdZn intermediates were formed during the atomization process. Density functional theory revealed that the formation of PdZn helped the generation of vacancies adjacent to metal nanoparticles, which prompted the atomization process. This strategy can be facilely applied to the atomization of sulfur-poisoned commercial Pd/C, which shows the potential for recycling commercial catalysts. The optimal Pd 1 /N, S-C catalyst showed good activity and much enhanced selectivity than Pd 4 S for the semi-hydrogenation of acetylene.

Electronic structure is essential to understanding the catalytic mechanism of metal single-atom catalysts (SACs), especially under electrochemical conditions. This study delves into the nuanced modulation of "frontier orbitals" in SACs on nitrogen-doped graphene (N-C) substrates by electrochemical potentials. We observe shifts in Fermi level and changes of d-orbital occupation with alterations in electrochemical potentials, emphasizing a synergy between the discretized atomic orbitals of metals and the continuous bands of the N-C based environment. Using O 2 and CO 2 as model adsorbates, we highlight the direct consequences of these shifts on adsorption energies, unveiling an intriguing inversion of adsorption energies on Co/N-C SAC under negative electrochemical potentials. Such insights are attributed to the role of the d xz and d z 2 orbitals, pivotal for stabilizing the π* orbitals of O 2 . Through this exploration, our work offers insights on the interplay between electronic structures and adsorption behaviors in SACs, paving the way for enhanced catalyst design strategies in electrochemical processes.

Downsizing metal nanoparticles to single atoms (monoatomization of nanoparticles) has been actively pursued to maximize the metal utilization of noble-metal-based catalysts and regenerate the activity of agglomerated metal catalysts. However, precise control of monoatomization to optimize the catalytic performance remains a great challenge. Herein, we developed a laser ablation strategy to achieve the accurate regulation of Pt nanoparticles (Pt NP ) to Pt single atoms (Pt 1 ) conversion on CeO 2 . Owing to the excellent tunability of input laser energy, the proportion of Pt 1 versus total Pt on CeO 2 can be precisely controlled from 0 to 100% by setting different laser powers and irradiation times. The obtained Pt 1 Pt NP /CeO 2 catalyst with approximately 19% Pt 1 and 81% Pt NP exhibited much-enhanced CO oxidation activity than Pt 1 /CeO 2 , Pt NP /CeO 2 , and other Pt 1 Pt NP /CeO 2 catalysts. Density functional theory (DFT) calculations showed that Pt NP was the major active center for CO oxidation, while Pt 1 changed the chemical potential of lattice oxygen on CeO 2 , which decreased the energy barrier required for CO oxidation by lattice oxygen and resulted in an overall performance improvement. This work provides a reliable strategy to redisperse metal nanoparticles for designing catalysts with various single-atom/nanoparticle ratios from a top-down path and valuable insights into understanding the synergistic effect of nano-single-atom catalysts.

Exploring the transformation/interconversion pathways of catalytic active metal species (single atoms, clusters, nanoparticles) on a support is crucial for the fabrication of high-efficiency catalysts, the investigation of how catalysts are deactivated, and the regeneration of spent catalysts. Sintering and redispersion represent the two main transformation modes for metal active components in heterogeneous catalysts. Herein, we established a novel solid-state atomic replacement transformation for metal catalysts, through which metal atoms exchanged between single atoms and nanoalloys to form a new set of nanoalloys and single atoms. Specifically, we found that the Ni of the PtNi nanoalloy and the Zn of the ZIF-8-derived Zn 1 on nitrogen-doped carbon (Zn 1 -CN) experienced metal interchange to produce PtZn nanocrystals and Ni single atoms (Ni 1 -CN) at high temperature. The elemental migration and chemical bond evolution during the atomic replacement displayed a Ni and Zn mutual migration feature. Density functional theory calculations revealed that the atomic replacement was realized by endothermically stretching Zn from the CN support into the nanoalloy and exothermically trapping Ni with defects on the CN support. Owing to the synergistic effect of the PtZn nanocrystal and Ni 1 -CN, the obtained (PtZn) n /Ni 1 -CN multisite catalyst showed a lower energy barrier of CO 2 protonation and CO desorption than that of the reference catalysts in the CO 2 reduction reaction (CO 2 RR), resulting in a much enhanced CO 2 RR catalytic performance. This unique atomic replacement transformation was also applicable to other metal alloys such as PtPd.

Sintering during heterogeneous catalytic reactions is one of the most notorious deactivation channels in catalysts of supported metal nanoparticles. It is therefore critical to understand the effect of support on the sintering behavior. Here, by using in situ aberration-corrected transmission electron microscopy and computational modeling, the atomic-scale dynamic interactions are revealed between Au nanoparticles and various supports. It is found that Au nanoparticles on ceria have a smaller contact angle and are apparently less mobile, especially at surface steps when compared with those on the amorphous silica. Analogous to hydrophilicity, we attribute the origin of mobility of small nanoparticles to metal affinity, which determines the interaction between metal and support material. Ab initio molecular dynamics (AIMD) and machine learning-based deep potential molecular dynamics (DPMD) simulations directly capture a coalescence process on the silica surface and the strong pinning of gold on ceria. The joint experimental and theoretical results on the atomic scale demonstrate the metal affinity of active and inert supports as the key descriptor pertinent to sintering and deactivation of heterogeneous catalysts.

Identification of catalytic active sites is pivotal in the design of highly effective heterogeneous metal catalysts, especially for structure-sensitive reactions. Downsizing the dimension of the metal species on the catalyst increases the dispersion, which is maximized when the metal exists as single atoms, namely, single-atom catalysts (SACs). SACs have been reported to be efficient for various catalytic reactions. We show here that the Pt SACs, although with the highest metal atom utilization efficiency, are totally inactive in the cyclohexane (C 6 H 12 ) dehydrogenation reaction, an important reaction that could enable efficient hydrogen transportation. Instead, catalysts enriched with fully exposed few-atom Pt ensembles, with a Pt-Pt coordination number of around 2, achieve the optimal catalytic performance. The superior performance of a fully exposed few-atom ensemble catalyst is attributed to its high d-band center, multiple neighboring metal sites, and weak binding of the product.

A ferroelectric/ferroelastic is a material whose spontaneous polarization/strain can be switched by applying an external electric field/mechanical stress. However, the optical control of spontaneous polarization/strain remains relatively unexplored in crystalline materials, although photoirradiation stands out as a nondestructive, noncontact, and remote-controlled stimulus beyond stress or electric field. Here, we present two new organic single-component homochiral photochromic multiferroics, ( R )- and ( S )- N -3,5-di- tert -butylsalicylidene-1-4-bromophenylethylamine (SA-Ph-Br( R ) and SA-Ph-Br( S )), which show a full ferroelectric/ferroelastic phase transition of 222F2 type at 336 K. Under photoirradiation, their spontaneous polarization/strain can be switched quickly within seconds and reversibly between two ferroelectric/ferroelastic phases with the respective enol and trans -keto forms triggered by structural photoisomerizations. In addition, they possess a superior acoustic impedance characteristic with a value of ∼2.42 × 10 6 kg·s -1 ·m -2 , lower than that of polyvinylidene fluoride (PVDF, (3.69-4.25) × 10 6 kg·s -1 ·m -2 ), which can better match human tissues. This work realizes for the first time that multiple ferroic orders in single-component organic crystals with ultralow acoustic impedance can be simultaneously controlled and coupled by three physical channels (electric, stress, light fields), suggesting their great potential in multichannel data storage, optoelectronics, and related applications compatible with all-organic electronics and human tissues.

The optical control of polarization switching is attracting tremendous interest because photoirradiation stands out as a nondestructive, noncontact, and remote-control means beyond an electric or strain field. The current research mainly uses various photoexcited electronic effects to achieve the photocontrol polarization, such as a light-driven flexoelectric effect and a photovoltaic effect. However, since photochromism was discovered in 1867, the structural phase transition caused by photoisomerization has never been associated with ferroelectricity. Here, we successfully synthesized an organic photochromic ferroelectric with polar space group Pna 2 1 , 3,4,5-trifluoro- N -(3,5-di- tert -butylsalicylidene)aniline, whose color can change between yellow and orange via laser illumination. Its dielectric permittivity and spontaneous polarization can be switched reversibly with a photoinduced phase transition triggered by structural photoisomerization between the enol form and the trans -keto form. To our knowledge, this is the first photoswitchable ferroelectric crystal to achieve polarization switching through a structural phase transition triggered by photoisomerization. This finding paves the way toward photocontrol of smart materials and biomechanical applications in the future.

Single-atom catalysts (SACs) and single-cluster catalysts (SCCs) are the new frontier of heterogeneous catalysis, which exhibit high activity, selectivity, stability, and atomic efficiency as well as precise tunability. However, the lack of efficient methods for producing high-loading and high-purity SACs and SCCs hinders their industrial applications. In this work, we propose a general and efficient strategy for the production of high-loading and high-purity SACs and SCCs anchored on suitable substrates. Our strategy relies on the existence of an electrochemical potential window (EcPW) we predict within which any aggregate forms of the target metal on the substrate are leached away by electrochemical oxidation, while the strongly bound single atoms or single clusters remain at the substrate. We demonstrate the applicability of this strategy with modeling the production of Pt, Pd, and Ni SACs anchored on N-doped graphene and Fe 2 O 3 as well as Pt 3 and Ni 3 SCCs anchored on graphdiyne.

The ammonia synthesis from N 2 is of vital importance, with imitating biological nitrogen fixation attracted much interest. Herein, we investigate the catalytic mechanisms of N 2 -to-NH 3 thermal conversion on the singly dispersed bimetallic catalyst Rh 1 Co 3 /CoO(011), and find that the preferred pathway is an associative mechanism analogous to the biological process, in which alternating hydrogenations of the N 2 occur, with H 2 activation on both metal sites. We propose that the singly dispersed bimetallic M 1 A n catalyst, in which the doped metal atom M substitutes an oxygen atom on the oxide surface of metal A, serves as a new surface single-cluster catalyst (SCC) design platform for the biomimetic N 2 -to-NH 3 thermal conversion. The catalytic ability of M 1 A n catalyst is attributed to both the charge buffer capacity of doped metal M and the complementary role of synergic metal A in catalysis. Our work provides insights and guidelines for further optimizing the M 1 A n catalyst.

We have constructed a general thermodynamic model of chemical potentials and applied ab initio electronic structure and molecular dynamics simulations, as well as kinetic Monte Carlo analysis, to probe the dynamical, reactive, and kinetic aspects of metal single-atom catalysts (SACs) on oxide support. We choose Au single atoms (SAs) supported on ceria as a typical example to demonstrate how our model can guide the rational design of highly stable and reactive SACs. It is shown that, under realistic conditions, various factors such as temperature, pressure, particle size, and the reducibility of the support can strongly affect both the stability and the reactivity of SACs by altering the relative chemical potentials between SAs and metal nanoparticles (NPs). The Au SAs at step sites of ceria support are rather stable, even at temperatures as high as 700 K, and exhibit around 10 orders of magnitude more reactivity for CO oxidation than the terrace sites. Remarkably, under reaction conditions, Au SAs can be dynamically created at the interface of small-size Au NPs on ceria support even without step sites, which accounts for the puzzling significant size effect in gold catalysis. Our work underscores an unrecognized critical role of Au SAs in gold nanocatalysis and provides a general methodology for designing the metal SACs on oxide supports.

We present the first experimental vibrational spectroscopy study providing direct evidence of a water phase inside single-walled carbon nanotubes that exhibits an unusual form of hydrogen-bonding due to confinement. Water adopts a stacked-ring structure inside nanotubes, forming intra- and inter-ring hydrogen bonds. The intra-ring hydrogen bonds are bulk-like while the inter-ring hydrogen bonds are relatively weak, having a distorted geometry that gives rise to a distinct OH stretching mode. The experimentally observed infrared mode at 3507 cm(-1) is assigned to vibrations of the inter-ring OH-groups based on detailed atomic-level modeling. The direct observation of unusual hydrogen bonding in nanotubes has potential implications for water in other highly confined systems, such as biological channels and nanoporous media.