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Allylation using allylic alcohols is environmentally friendly because water is the only by-product. Allylic alcohols are one of the most unreactive allylating agents for homogeneous Pd-catalyzed allylation; however, they can undergo electrophilic activation with acidic active species. Heterogeneous catalysts are known for their unique catalytic performance due to the concerted effect of the immobilized metal center and support material surface. Our group has developed a mesoporous-silica-supported Pd complex catalyst that promotes the Tsuji–Trost allylation of dicarbonyl compounds with allylic alcohols through the concerted effect of Pd and surficial silanol groups. In this work, to enhance the catalytic activity of the supported Pd complex for allylation with allylic alcohols, the acidity of the support was increased by doping the silicate backbone with aluminum. Several spectroscopic techniques, such as Pd K-edge X-ray absorption fine structure (XAFS), solid-state NMR, and pyridine adsorption FT-IR measurements, were applied to confirm the structure of the catalyst. The Pd complex catalyst immobilized on an Al-doped support showed enhanced catalytic activity in allylation owing to the activation of the allylic alcohol by both the Al Lewis acid sites and silanol groups. The site-selective immobilization of the Pd complex through a silane-coupling reaction on Brønsted acid sites (Si–O(H+)–Al) enhances the concerted effect between the Pd complex and Lewis acidic Al sites on the MS surface.

Mesoporous silica-supported Rh complexes alongside organic functional groups enable 1,4-addition reaction in water.

Iron carbide clusters with near-sub-nanometer size have been synthesized by employing a tetraphenylmethane-cored phenylazomethine dendrimer generation 4 (TPM-DPAG4) as a molecular template. Magnetic measurements reveal that these iron carbide clusters exhibit a magnetization-field hysteresis loop at 300 K. The data indicate that these iron carbide clusters are ferromagnets at room temperature.

The dehydrogenative coupling reaction of alkanes and benzene has attracted attention as a method of direct conversion of alkanes to raw materials for useful chemical products. Here, we report the first combined catalyst system composed of hydrotalcite-supported palladium and solid acid aluminum-exchanged montmorillonite for the direct alkylation of benzene promoted by slurry-phase interparticle hydrogen transfer at 150 °C. The combination of the two catalytic particles showed excellent activity and achieved the maximum benzene conversion of 21% and target product selectivity of 84% in the reaction of n-heptane and benzene. Our results, thus, provide a feasible strategy to design efficient liquid-phase reaction systems employing simple physical mixing of two catalytic particles.

We have developed a catalyst in which an Ir complex and organic functionalities are coimmobilized on the silica surface. The catalytic activity for aromatic C–H borylation was significantly affecte...

Carbothermal hydrogen reduction (CHR) is a unique dry chemical process used to fabricate metals and carbides on carbon supports. In this study, a stepwise CHR of WCl6 on a graphite support is demonstrated for the first time. Powder X-ray diffraction studies revealed that, at 773 K, metallic tungsten nanoparticles are produced, whereas, at 1073 K, the metastable W2C phase is generated rather than the thermodynamically stable WC phase. X-ray photoelectron spectroscopy and X-ray absorption near edge structure studies showed that the chemical state of the W nanoparticles simultaneously exhibits metallic W(∼0) and carbide W(δ+) character. The obtained results suggest that, although electronic interactions exist between the metallic W atoms and the graphite support, the body-centered cubic structure of the metallic tungsten is maintained, confirmed by the extended X-ray absorption fine structure. In addition, high-resolution scanning transmission electron microscopy observations revealed that the W nanoparticles exhibit a thin flattened shape on the support. These results support the notion that the mechanism for the formation of the W nanoparticles during the CHR is influenced by the electronic interactions between the W nanoparticles and the graphite support. Our work thus suggests that the combination of early-transition-metal atoms and carbon-based supports would afford modulatable electronic systems though the electronic interactions.

Microwave irradiation can cause high local temperatures at supported metal nanoparticles, which can enhance reaction rates. Here we discuss the temperature of platinum nanoparticles on γ-Al2O3 and SiO2 supports under microwave irradiation using the Debye–Waller factor obtained from in situ extended X-ray absorption fine structure (EXAFS) measurements. Microwave irradiation exhibits considerably smaller Deby–Waller factors than conventional heating, indicating the high local temperature at the nanoparticles. The difference in the average temperatures between the platinum nanoparticles and the bulk under microwaves reaches 26 K and 132 K for Pt/Al2O3 and Pt/SiO2, respectively. As a result, Pt/SiO2 exhibits considerably more reaction acceleration for the catalytic dehydrogenation of 2-propanol under microwave irradiation than Pt/Al2O3. We also find microwaves enhance the reduction of PtOx nanoparticles by using operando X-ray absorption near edge structure (XANES) spectroscopy. The present results indicate that significant local heating of platinum nanoparticles by microwaves is effective for the acceleration of catalytic reactions. Microwave irradiation allows for direct and focused heating of solid catalysts, however, temperature control remains a major challenge. Here the local temperatures of platinum nanoparticles on γ-Al2O3 and SiO2 supports are elucidated with in situ XAFS and operando XANES spectroscopy.

Ultrasmall particles exhibit structures and/or properties that are different from those of the corresponding bulk materials; in this context especially ultrasmall precious-metal particles have been extensively investigated. In this study, we targeted the transition base-metal Mo and succeeded in systematically producing Mo oxycarbide/carbide particles with diameters of 1.7 ± 0.7, 1.4 ± 0.5, 1.3 ± 0.4, 1.2 ± 0.3, 1.0 ± 0.3, and 0.8 ± 0.2 nm on a carbon support using the carbothermal hydrogen reduction method at 773 K and a diphenylazomethine-type dendrimer as a template. The formation and properties of the particles were confirmed using X-ray photoelectron spectroscopy, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images, and X-ray absorption fine structure (XAFS) studies. We found that Mo particles with a diameter of 1.3 nm or greater formed carbides such as β'-Mo2C, whereas smaller particles formed oxycarbides, indicating a size-dependent transformation in the phase or composition of the particles. Thus, this work demonstrated a new concept, subnano-transformation, which would be a new class of phase transformation based on the concept of the size dependence in such an ultrasmall scale. In addition, the movement of Mo atoms within a cluster and on the fringes of a nanoparticle was also demonstrated during continuous time-course high-resolution HAADF-STEM observation.

Ultrasmall particles, different from the larger size nanoparticles, have recently attracted significant attention in the scientific community in nanotechnology for catalytic, electronic and optical applications; however, their magnetic properties remain unexplored due to the difficult structural analysis. A challenging issue is to develop a preparation method for iron oxide particles (IOPs) with fine size control, and to determine the dependence of magnetic properties on the morphology and crystallinity of the magnetic particles. However, synthetic approaches to obtain IOPs, regarded as one of the new fields of magnetic nanoparticles, have been significantly limited. This article reported a developed synthetic method to prepare IOPs on carbon supports using pulsed arc plasma deposition (APD) in flowing oxygen gas, which clarified the finely-controlled formation of IOPs on graphene nanosheets. Structural characterization of the IOPs revealed the formation of crystalline γ-Fe2O3 ultrasmall particles with oxygen deficiency. The pulsed APD method for IOPs is the first simple and convenient technique to not only prevent significant aggregation and contamination by organic compounds and avoid the need for thermal pretreatment, but also provide uniform crystalline nano-order particles.

Silica-supported Rh-ammonium iodide catalyst showed high performance for hydrosilylation-CO2 cycloaddition reaction sequences. The catalyst was prepared by surface grafting of Rh and the silane-coupling reaction of the ammonium iodide moiety. The acceleration of each catalytic reaction was realized due to the concerted catalysis between Rh species, immobilized organic functions, and surface Si-OH groups. As a result, good to excellent yields of silyl carbonates were obtained from epoxyolefins, hydrosilanes, and CO2 under mild reaction conditions.

Mesoporous silica-supported Rh complex catalysts were prepared by simple silane-coupling, followed by complexation, and characterized by FT-IR, SEM, Rh K-edge XAFS, and elemental analysis. Local structures of the Rh complexes in each sample were almost similar to those of a nonporous silica-supported diaminorhodium complex. Co-immobilization of a tertiary amine on the same silica surface induced slight changes to the Rh complex structure in the case of the support with smaller pores. The prepared catalysts showed high activity for the 1,4-addition reaction of phenylboronic acids. Co-immobilization of the tertiary amine increased the reaction rate by more than 7-fold, with turnover number of nearly 8500. The catalytic performance achieved with this novel system is with much higher than that reported previously with a nonporous silica-supported catalyst. The mesoporous silica-supported Rh complex-tertiary amine showed a wide substrate scope, including unsaturated ketones and nitriles. This co-immobilized tertiary amine may activate phenylboronic acid to enhance its reactivity in the transmetalation step with Rh-OH species.

Co-immobilization of a Rh complex and a tertiary amine on the same silica surface enhances the hydrosilylation reaction of olefins. In our previous study, the silica-supported Rh complex-tertiary amine catalyst (SiO2/Rh-NEt2) showed higher activity than a silica-supported Rh complex (SiO2/Rh) alone. Herein, the influence of the amine on the local structure of the Rh complex was evaluated by DNP-enhanced solid-state 15N NMR spectroscopy and Rh K-edge XAFS measured at 20 K. The amine distorts the structure of the cyclooctadiene (COD) ligand in the Rh complex immobilized on the silica surface. The reactivity of the COD ligand with hydrosilane was confirmed by the in situ FTIR spectra, and it was found that the presence of an amine facilitates COD dissociation from the Rh center. This phenomenon accelerates the ligand exchange process in Rh-catalyzed hydrosilylation.

Invited for the cover of this issue is Kimihisa Yamamoto and co-workers at Tokyo Institute of Technology and International Christian University. The image depicts enhanced reactivity of the copper oxide subnanoparticles under low-temperature conditions. Read the full text of the article at 10.1002/chem.202100508.

Carbothermal hydrogen reduction (CHR) is a unique dry chemical process used to fabricate metals and carbides on carbon supports. In this study, a stepwise CHR of WCl

Variable-temperature Pd K-edge X-ray absorption fine structure analysis of SiO2-supported Pd complexes with and without a co-immobilized organic functionality was conducted. Both samples maintained their coordination numbers, interatomic distances, and Debye–Waller factors at temperature of 25–300 K. Based on the obtained results, the Debye–Waller factor differences between these samples were ascribed to static disorder variability caused by the steric effect of the co-immobilized organic functionality.

Graphene growth on a Pt(111) substrate exposed to benzene was studied at substrate temperatures between 800 K and 1100 K. The effects of the substrate temperature during benzene exposure and post-annealing were examined. It was revealed that the substrate temperature during benzene exposure determined the graphene size, which was measured using scanning tunneling microscopy (STM). Nanographenes (NGs) of ~10 nm in size. were obtained by exposing the substrate to benzene at 800 K and post-annealing at 1100 K. The presence of a C–Pt bond, which may fix the carbon atoms on the Pt(111) surface and suppress any further growth of graphene, was confirmed by the carbon K-edge near-edge X-ray absorption fine structure spectroscopy (C K NEXAFS) and X-ray photoelectron spectroscopy (XPS) for the NG. Angle resolved photoemission spectroscopy (ARPES) performed on the NG has a reduced density of states at the Fermi level.

The surface of mesoporous silica was modified with a Pd–bisphosphine complex and/or a tertiary amine group for concerted acceleration of allylation reactions. Mesoporous-silica-supported catalysts with a 1.6 nm pore diameter showed higher performance than nonporous or larger mesoporous silica-supported catalysts owing to the accumulation of active sites into a confined space. For the case in which allyl alcohol was used in the reaction, the presence of a silanol group on the surface was quite effective: the turnover number of Pd was nine times greater than that of the homogeneous Pd complex.

The simultaneous immobilization of a Rh complex and a tertiary amine on a SiO2 surface afforded a highly active supported catalyst for the hydrosilylation of terminal olefins. The turnover number in the reaction using 0.00005 mol % of the Rh catalyst approached 1 900 000 over 24 h. A broad range of terminal olefins and hydrosilanes acted as good substrates, giving their corresponding hydrosilylation products in excellent yields. CSI-mass analysis of the precursor solution containing the Rh complex and tertiary amine indicated complexation between these two precursors. The resultant close positioning of the Rh complex and amine after attachment onto SiO2 surface led to excellent catalysis.

Silica-supported Rh-ammonium iodide catalyst showed high performance for hydrosilylation-CO

Subnanoparticles (SNPs) with sizes of approximately 1 nm are attractive for enhancing the catalytic performance of transition metals and their oxides. Such SNPs are of particular interest as redox-active catalysts in selective oxidation reactions. However, the electronic states and oxophilicity of copper oxide SNPs are still a subject of debate in terms of their redox properties during oxidation reactions for hydrocarbons. In this work, in situ X-ray absorption fine structure (XAFS) measurements of Cu28 Ox SNPs, which were prepared by using a dendritic phenylazomethine template, during temperature-programmed reduction (TPR) with H2 achieved lowering of the temperature (T50 =138 °C) reported thus far for the CuII →CuI reduction reaction because of Cu-O bond elongation in the ultrasmall copper oxide particles.

Organic molecular layers with viologen moieties as electron transfer mediators were constructed on hydrogen-terminated Si(111) surfaces, and metal catalysts for multielectron transfer reactions were incorporated into the molecular layers by immersing the viologen-modified Si(111) electrodes in aqueous solutions containing various metal complexes (K2PdCl4, NaAuCl4, and K2PtCl4). Significant enhancements were achieved for CO2 reduction at the Au-modified Si(111) electrode and for both hydrogen evolution reaction (HER) and CO2 reduction at the Pd-modified Si(111) electrode. X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) analysis showed that Au complexes were spontaneously reduced to metal nanoparticles during the metal insertion, and therefore, actual catalysts for CO2 reduction at the Au-modified Si(111) electrode were Au metal nanoparticles. In contrast, Pd complexes were inserted into the molecular layers and partly reduced during HER and CO2 reduction. Pd complexes and ...

Ni and Pt structures evaporated onto a TiO2(110) surface premodified with ortho-mercaptobenzoic acid (o-MBA) were studied using polarization-dependent total reflection fluorescence X-ray absorption fine structure analysis to determine the effects of the premodification on the dispersion of the metal atoms over the TiO2(110) surface. Ni was found to be atomically dispersed with the formation of S–Ni–O bonds (where the S is provided by the o-MBA and the O is present in the TiO2 lattice) on the surface. In contrast, Pt underwent aggregation to form small clusters. The varying behavior of these metals on the o-MBA-modified TiO2(110) surface is discussed based on the energy difference between sulfur–metal–oxygen and metal–metal bond formations, and we propose a new indicator for single metal dispersion on the TiO2(110) surface.

Correction for ‘A Pd–bisphosphine complex and organic functionalities immobilized on the same SiO2 surface: detailed characterization and its use as an efficient catalyst for allylation’ by Ken Motokura et al., Catal. Sci. Technol., 2016, DOI: 10.1039/c6cy00593d.

In this study, mesoporous and nonporous silica-supported Pd complexes were synthesized and characterized. Variable-temperature XAFS measurements and a curve-fitting analysis showed a slightly larger contribution of σ2static when the Pd complexes were on a nonporous support in comparison to a mesoporous support. In contrast, the catalytic performance of the attached Pd complex in the Suzuki-Miyaura cross-coupling reaction was not affected by such small differences in the static disorder of the Pd complex.

X-ray-aided noncontact atomic force microscopy (XANAM) is a spectroscopic and imaging technique in the combination of noncontact atomic force microscopy (NC-AFM) and synchrotron radiation (SR) X-ray, providing chemical imaging of sample surface beneath the AFM tip (Suzuki in J Phys: Conf Ser 61:1117–1121, 2007; Suzuki in Bull. Chem Soc Jpn 88:240–250, 2015[1]).

Co-immobilization of a palladium–bisphosphine complex and a strong organic base, 1,4-diazabicyclo[2.2.2]octane (DABCO), on a silica support was successfully achieved. The new catalyst structure was characterized by X-ray photoelectron spectroscopy, solid-state NMR spectroscopy, X-ray absorption fine structure spectroscopy, and elemental analysis. Although the local structure of the Pd–bisphosphine complex was unaffected by the presence of DABCO on the same silica surface, its catalytic activity in allylation reactions of nucleophiles was significantly enhanced, achieving turnover numbers (TON) up to >10 000, owing to dual-activation of substrate molecules by the Pd complex and DABCO.

On a subnanometer scale, an only one-atom difference in a metal cluster may cause significant transitions in the catalytic activity due to the electronic and geometric configurations. We now report the atomicity-specific catalytic activity of platinum clusters with significantly small atomicity, especially below 20. The atomic coordination structure is completely different from that of the larger face-centered cubic (fcc) nanocrystals. Here, an electrochemical study on such small clusters, in which the atomicity ranged between 12 and 20, revealed Pt19 as the most catalytically active species. In combination with a theoretical study, a common structure that leads to a high catalytic performance is proposed.

Double-activation catalysis by a rhodium complex/tertiary amine catalyst for the 1,4-addition of organoboronic acids was investigated. A rhodium complex and a tertiary amine were co-immobilized on the same silica surface by silane-coupling reactions followed by complexation of the Rh species. Structures of the Rh complex and tertiary amine on the silica surface were determined by solid-state 13C and 29Si MAS NMR, XAFS, and XPS measurements. The immobilized tertiary amine accelerated the Rh-catalyzed 1,4-addition of phenylboronic acid to cyclohexenone. The role of the anchored tertiary amine in the 1,4-addition reaction was clarified by solid-state 11B MAS NMR: it activates the arylboronic acid forming a four-coordinate boron species, which then accelerates the transmetallation step in the Rh complex-catalyzed 1,4-addition. The silica-supported Rh complex/tertiary amine catalyst system could be applicable to the reaction of various aryl- and even alkyl-boronic acids.

Subnanometer noble metal clusters have enormous potential, mainly for catalytic applications. Because a difference of only one atom may cause significant changes in their reactivity, a preparation method with atomic-level precision is essential. Although such a precision with enough scalability has been achieved by gas-phase synthesis, large-scale preparation is still at the frontier, hampering practical applications. We now show the atom-precise and fully scalable synthesis of platinum clusters on a milligram scale from tiara-like platinum complexes with various ring numbers (n = 5–13). Low-temperature calcination of the complexes on a carbon support under hydrogen stream affords monodispersed platinum clusters, whose atomicity is equivalent to that of the precursor complex. One of the clusters (Pt10) exhibits high catalytic activity in the hydrogenation of styrene compared to that of the other clusters. This method opens an avenue for the application of these clusters to preparative-scale catalysis., The catalytic activity of a noble metal nanocluster is tied to its atomicity. Here, the authors report an atom-precise, fully scalable synthesis of platinum clusters from molecular ring precursors, and show that a variation of only one atom can dramatically change a cluster’s reactivity.

Multimetallic nanoclusters are synthesized using a dendrimer exhibited high activities for catalytic oxidation of hydrocarbons., The catalytic activity of alloy nanoparticles depends on the particle size and composition ratio of different metals. Alloy nanoparticles composed of Pd, Pt, and Au are widely used as catalysts for oxidation reactions. The catalytic activities of Pt and Au nanoparticles in oxidation reactions are known to increase as the particle size decreases and to increase on the metal-metal interface of alloy nanoparticles. Therefore, multimetallic nanoclusters (MNCs) around 1 nm in diameter have potential as catalysts for oxidation reactions. However, there have been few reports describing the preparation of uniform alloy nanoclusters. We report the synthesis of finely controlled MNCs (around 1 nm) using a macromolecular template with coordination sites arranged in a gradient of basicity. We reveal that Cu-Pt-Au MNCs supported on graphitized mesoporous carbon show catalytic activity that is 24 times greater than that of a commercially available Pt catalyst for aerobic oxidation of hydrocarbons. In addition, solvent-free aerobic oxidation of hydrocarbons to ketones at room temperature, using small amounts of a radical initiator, was achieved as a heterogeneous catalytic reaction for the first time.

Efficient hydrolytic hydrogenation of cellulose to sugar alcohols under low H2 pressures has remained a challenge. This article deals with the conversion of cellulose by using a carbon-supported Ru catalyst under H2 pressures as low as 0.7–0.9 MPa (absolute pressure at room temperature). Kinetic studies revealed that the Ru catalyst not only enhances the hydrolysis of cellulose to glucose and hydrogenation of glucose to sugar alcohols (sorbitol and mannitol), but also the degradation of sugar alcohols to C2–C6 polyols and gasses. The degradation path limits the total yield of sugar alcohols to less than 40 %. The yield of sugar alcohols is theoretically improved by increasing the ratio of the reaction rates of the cellulose hydrolysis, which is the rate-determining step in the reaction, to the decomposition. Thus, a mix-milling pretreatment of cellulose and the Ru catalyst together selectively accelerated the hydrolysis step and raised the yield up to 68 %, whereas the addition of acids in the cellulose conversion was less effective as a result of promotion of side-reactions. These results demonstrate superior applicability of the mix-milling treatment in the depolymerization of cellulose to its monomers.

A relationship between the size of metal particles and their catalytic activity has been established over a nanometer scale (2-10 nm). However, application on a subnanometer scale (0.5-2 nm) is difficult, a possible reason being that the activity no longer relies on the size but rather the geometric structure as a cluster (or superatomic) compound. We now report that the catalytic activity for the oxygen reduction reaction (ORR) significantly increased when only one atom was removed from a magic number cluster composed of 13-platinum atoms (Pt13). The synthesis with an atomic-level precision was successfully achieved by using a dendrimer ligand as the macromolecular template strictly defining the number of metal atoms. It was quite surprising that the Pt12 cluster exhibited more than 2-fold catalytic activity compared with that of the Pt13 cluster. ESI-TOF-mass and EXAFS analyses provided information about the structures. These analyses suggested that the Pt12 has a deformed coordination, while the Pt13 has a well-known icosahedral atomic coordination as part of the stable cluster series. Theoretical analyses based on density functional theory (DFT) also supported this idea. The present results suggest potential activity of the metastable clusters although they have been "missing" species in conventional statistical synthesis.