Enhancement effect of strong metal-support interaction (SMSI) on the catalytic activity of substituted-hydroxyapatite supported Au clusters

Recent Progress in the Design and Application of Strong Metal-Support Interactions in Electrocatalysis

The strong metal-support interaction (SMSI) in supported metal catalysts represents a crucial factor in the design of highly efficient heterogeneous catalysts. This interaction can modify the surface adsorption state, electronic structure, and coordination environment of the supported metal, altering the interface structure of the catalyst. These changes serve to enhance the catalyst's activity, stability, and reaction selectivity. In recent years, a multitude of researchers have uncovered a range of novel SMSI types and induction methods including oxidized SMSI (O-SMSI), adsorbent-mediated SMSI (A-SMSI), and wet chemically induced SMSI (Wc-SMSI). Consequently, a systematic and critical review is highly desirable to illuminate the latest advancements in SMSI and to deliberate its application within heterogeneous catalysts. This article provides a review of the characteristics of various SMSI types and the most recent induction methods. It is concluded that SMSI significantly contributes to enhancing catalyst stability, altering reaction selectivity, and increasing catalytic activity. Furthermore, this paper offers a comprehensive review of the extensive application of SMSI in the electrocatalysis of hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and carbon dioxide reduction reaction (CO2RR). Finally, the opportunities and challenges that SMSI faces in the future are discussed.

Preparation and Catalytic Properties of Gold Single-Atom and Cluster Catalysts Utilizing Nanoparticulate Mg-Al Layered Double Hydroxides

Au single atoms and clusters were stabilized on Mg-Al layered double hydroxide nanoparticles (LDH NPs), and the obtained Au@LDH NPs were supported on SiO2 and CeO2. After hydrogen reduction, Au single atoms were found together with Au clusters on LDH/SiO2. In contrast to Au single-atom catalysts which are deposited in metal vacancies of oxide supports, the LDH NPs stabilize very small Au species despite the absence of metal vacancies. The obtained Au(0)@LDH/SiO2 catalyzed aerobic oxidation of alcohols, and Au single atoms maintained after the reaction. Given that only Au NPs were observed on bulk LDH, the abundant surface OH group of LDH NPs would contribute to stabilize Au, resulting in higher activity than Au/LDH-bulk. After calcination to transform LDH to mixed metal oxide (MMO), the obtained Au(0)@MMO/SiO2 also exhibited high catalytic activity. Moreover, Au(0)@LDH/CeO2 exhibited higher activity and excellent selectivity for hydrogenation of 4-nitrostyrene to 4-aminostyrene than conventional Au catalysts such as Au/CeO2 and Au/TiO2. We demonstrated that Au size can be minimized using LDH NPs, exhibiting high catalytic performance. The basic surface OH groups of LDH would be also beneficial for deprotonation of alcohols and heterolytic dissociation of H2 in the catalytic reactions.

Cobalt-Hydride-Catalyzed Alkene-Carboxylate Transposition (ACT) of Allyl Carboxylates

The alkene-carboxylate transposition (ACT) of allyl carboxylates is one of the most atom-economic and synthetically reliable transformations in organic chemistry, as allyl carboxylates are versatile synthetic intermediates. Classic ACT transformations, including [3,3]-sigmatropic rearrangement and transition metal-catalyzed allylic rearrangement, typically yield 1,2-alkene/1,3-acyloxy shifted products through a two-electron process. However, position-altered ACT to produce distinct 1,3-alkene/1,2-acyloxy shifted products remains elusive. Here, we report the first cobalt-hydride-catalyzed ACT of allyl carboxylates, enabling access to these unprecedented 1,3-alkene/1,2-acyloxy shifted products via a 1,2-radical migration (RaM) strategy. This transformation demonstrates broad functional group tolerance, is suitable for late-stage modification of complex molecules, and is amenable to gram-scale synthesis. It also expands the reaction profiles of both allyl carboxylates and cobalt catalysis. Preliminary experimental and computational studies suggest a mechanism involving metal-hydride hydrogen atom transfer (MHAT) and the 1,2-RaM process. This reaction is expected to serve as the basis for the development of versatile Co-H-catalyzed transformations of allyl carboxylates, generating a wide array of valuable building blocks for synthetic, medicinal, and materials chemistry.

Strong metal-support interaction (SMSI) in environmental catalysis: Mechanisms, application, regulation strategies, and breakthroughs

The strong metal-support interaction (SMSI) in supported catalysts plays a dominant role in catalytic degradation, upgrading, and remanufacturing of environmental pollutants. Previous studies have shown that SMSI is crucial in supported catalysts' activity and stability. However, for redox reactions catalyzed in environmental catalysis, the enhancement mechanism of SMSI-induced oxygen vacancy and electron transfer needs to be clarified. Additionally, the precise control of SMSI interface sites remains to be fully understood. Here we provide a systematic review of SMSI's catalytic mechanisms and control strategies in purifying gaseous pollutants, treating organic wastewater, and valorizing biomass solid waste. We explore the adsorption and activation mechanisms of SMSI in redox reactions by examining interfacial electron transfer, interfacial oxygen vacancy, and interfacial acidic sites. Furthermore, we develop a precise regulation strategy of SMSI from systematical perspectives of interface effect, crystal facet effect, size effect, guest ion doping, and modification effect. Importantly, we point out the drawbacks and breakthrough directions for SMSI regulation in environmental catalysis, including partial encapsulation strategy, size optimization strategy, interface oxygen vacancy strategy, and multi-component strategy. This review article provides the potential applications of SMSI and offers guidance for its controlled regulation in environmental catalysis.

Meso-Macroporous Hydroxyapatite Powders Synthesized in Polyvinyl Alcohol or Polyvinylpyrrolidone Media

Mesoporous hydroxyapatite (HA) is widely used in various applications, such as the biomedical field, as a catalytic, as a sensor, and many others. The aim of this work was to obtain HA powders by means of chemical precipitation in a medium containing a polymer-polyvinyl alcohol or polyvinylpyrrolidone (PVP)-with concentrations ranging from 0 to 10%. The HA powders were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, atomic emission spectroscopy with inductively coupled plasma, electron paramagnetic resonance, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The specific surface area (SSA), pore volume, and pore size distributions were determined by low-temperature nitrogen adsorption measurements, and the zeta potential was established. The formation of macropores in powder agglomerates was determined using SEM and TEM. The synthesis in 10% PVP increased the SSA from 101.3 to 158.0 m2/g, while the ripening for 7 days led to an increase from 112.3 to 195.8 m2/g, with the total pore volume rising from 0.37 to 0.71 cm3/g. These materials could be classified as meso-macroporous HA. Such materials can serve as the basis for various applications requiring improved textural properties and may lay the foundation for the creation of bulk 3D materials using a technique that allows for the preservation of their unique pore structure.

Decoration of Gold and Platinum Nanoparticle Catalysts by 1 nm Thick Metal Oxide Overlayer and Its Effect on the CO Oxidation Activity

Exfoliated M-Al layered double hydroxide (M-Al LDH; M = Mg, Co, Ni, and Zn) nanosheets were adsorbed on Au/SiO2 and calcined to transform LDH into mixed metal oxides (MMOs) and yield Au/SiO2 coated with a thin MMO overlayer. These catalysts showed a higher catalytic activity than pristine Au/SiO2. In particular, the 50% CO conversion temperature decreased by more than 250 °C for Co-Al MMO-coated Au/SiO2. In contrast, the deposition of CoAlOx on Au/SiO2 by impregnation or the deposition of Au on Co-Al MMO-coated SiO2 resulted in a worse catalytic activity. Moreover, the presence of a thick MMO overlayer decreased the catalytic activity, suggesting that the control of the overlayer thickness to less than 1 nm is a requisite for obtaining a high catalytic activity. Moreover, the thin Co-Al MMO overlayer on Au/SiO2 possessed abundant oxygen vacancies, which would play an important role in O2 activation, resulting in a highly active interface between Au and the defect-rich MMO on the Au NP surface. Finally, this can be applied to Pt/SiO2, and the obtained Co-Al MMO-coated Pt/SiO2 also exhibited a much improved catalytic activity for CO oxidation.

Supported Noble Metal Catalysts and Adsorbents with Soft Lewis Acid Functions

Heterogeneous noble metal catalysts exhibit various functions. Although their redox functions have been extensively studied, we focused on their soft Lewis acid functions. Supported Au, Pt, and Pd catalysts electrophilically attack the π-electrons of soft bases such as alkynes, alkenes, and aromatic compounds to perform addition and substitution reactions. Hydroamination, intramolecular cyclization of alkynyl carboxylic acids, isomerization of allylic esters, vinyl exchange reactions, Wacker oxidation, and oxidative homocoupling of aromatics are introduced based on a discussion of the active species and reaction mechanisms. Furthermore, the adsorption of sulfur compounds, which are soft bases, onto the supported AuNPs is discussed. The adsorption and removal of 1,3-dimethyltrisulfane (DMTS), which is the compound responsible for the stale odor of "hine-ka" in alcoholic beverages, particularly Japanese sake, is described.

Design Strategies for Hydroxyapatite-Based Materials to Enhance Their Catalytic Performance and Applicability

Hydroxyapatite (HAP) is a green catalyst that has a wide range of applications in catalysis due to its high flexibility and multifunctionality. These properties allow HAP to accommodate a large number of catalyst modifications that can selectively improve the catalytic performance in target reactions. To date, many studies have been conducted to elucidate the effect of HAP modification on the catalytic activities for various reactions. However, systematic design strategies for HAP catalysts are not established yet due to an incomplete understanding of underlying structure-activity relationships. In this review, tuning methods of HAP for improving the catalytic performance are discussed: 1) ionic composition change, 2) morphology control, 3) incorporation of other metal species, and 4) catalytic support engineering. Detailed mechanisms and effects of structural modulations on the catalytic performances for attaining the design insights of HAP catalysts are investigated. In addition, computational studies to understand catalytic reactions on HAP materials are also introduced. Finally, important areas for future research are highlighted.

Diverse Alkyl-Silyl Cross-Coupling via Homolysis of Unactivated C(sp3)-O Bonds with the Cooperation of Gold Nanoparticles and Amphoteric Zirconium Oxides

Since C(sp³)-O bonds are a ubiquitous chemical motif in both natural and artificial organic molecules, the universal transformation of C(sp³)-O bonds will be a key technology for achieving carbon neutrality. We report herein that gold nanoparticles supported on amphoteric metal oxides, namely, ZrO₂, efficiently generated alkyl radicals via homolysis of unactivated C(sp³)-O bonds, which consequently promoted C(sp³)-Si bond formation to give diverse organosilicon compounds. A wide array of esters and ethers, which are either commercially available or easily synthesized from alcohols participated in the heterogeneous gold-catalyzed silylation by disilanes to give diverse alkyl-, allyl-, benzyl-, and allenyl silanes in high yields. In addition, this novel reaction technology for C(sp³)-O bond transformation could be applied to the upcycling of polyesters, i.e., the degradation of polyesters and the synthesis of organosilanes were realized concurrently by the unique catalysis of supported gold nanoparticles. Mechanistic studies corroborated the notion that the generation of alkyl radicals is involved in C(sp³)-Si coupling and the cooperation of gold and an acid-base pair on ZrO₂ is responsible for the homolysis of stable C(sp³)-O bonds. The high reusability and air tolerance of the heterogeneous gold catalysts as well as a simple, scalable, and green reaction system enabled the practical synthesis of diverse organosilicon compounds.