Boosted chlorate hydrogenation reduction via continuous atomic hydrogen.

XAFS investigation of nanopaticles supported on faujasite: Effect of hydrogen chemisorption on the atomic structure

Pressure-dependent product distribution of citral hydrogenation over micelle-hosted Pd and Ru nanoparticles in supercritical carbon dioxide

The 3-dimensional (3D) atomic-scale structure of newly discovered face-centered cubic (fcc) and conventional hexagonal close packed (hcp) type ruthenium (Ru) nanoparticles (NPs) of 2.2 to 5.4 nm diameter were studied using X-ray pair distribution function (PDF) analysis and reverse Monte Carlo (RMC) modeling. Atomic PDF based high-energy X-ray diffraction measurements show highly diffuse X-ray diffraction patterns for fcc- and hcp-type Ru NPs. We here report the atomic-scale structure of Ru NPs in terms of the total structure factor and Fourier-transformed PDF. It is found that the respective NPs have substantial structural disorder over short- to medium-range order atomic distances from the PDF analysis. The first-nearest-neighbor peak analyses show a significant size dependence for the fcc-type Ru NPs demonstrating the increase in the peak height due to an increase in the number density as a function of particle size. The bond angle and coordination number (CN) distribution for the RMC-simulated fcc- and hcp-type Ru NP models indicated inherited structural features from their bulk counterparts. The CN analysis of the whole NP and surface of each RMC model of Ru NPs show the low activation energy packing sites on the fcc-type Ru NP surface atoms. Finally, our newly defined order parameters for RMC simulated Ru NP models suggested that the enhancement of the CO oxidation activity of fcc-type NPs was due to a decrease in the close packing ordering that resulted from the increased NP size. These structural findings could be positively supported for synthesized low-cost and high performance nano-sized catalysts and have potential application in fuel-cell systems and organic synthesis.

Introduction Cobalt Fischer‐Tropsch Synthesis catalysts are generally doped with small amounts of noble metals that serve as reduction promoters to enhance the catalytic activity of the cobalt active sites [1] . This is because the promoter metals are able to dissociate hydrogen gas at a low temperature which then also lowers the reduction temperature of the cobalt oxide to cobalt. This then prevents easy deactivation of the cobalt catalysts that can be induced by high temperature activation. Hydrogen spillover has been invoked to explain the observed effect of these metals as promoters on cobalt catalysts. Two types of hydrogen spillover processes can be envisaged; (1) primary hydrogen spillover, whereby the promoter [i.e., initiator] is in contact with the cobalt oxide [i.e, acceptor] and the dissociated hydrogen atoms can move from the initiator through the direct interface to interact with the acceptor and (2) secondary hydrogen spillover, in this process the initiator and the acceptor materials are separated by some distance and hydrogen spillover can only happen by the dissociation of the hydrogen molecule on the initiator followed by a migration of the atomic hydrogen on a carrier (or catalyst support) to the acceptor material [i.e., cobalt oxide] [2]. Few model catalysts exist that can provide direct evidence of the existence of a type of hydrogen spillover that is dominant on Fischer‐Tropsch like catalysts. In this study mesoporous hollow carbon spheres (MHCS) were used as model supports to study whether both the primary and secondary hydrogen spillover were prominent during catalyst activation and Fischer‐Tropsch synthesis. Experimental MHCS were prepared as shown in Fig 1 (a). Three Co catalysts (15% loading) were prepared (1) Ru@MHCS@Co, with Ru nanoparticles and Co nanoparticles separated by the carbon shell, (2) CoRu/MHCS, Ru and Co co‐precipitated outside MHCS and (3) Co/MHCS, Co outside MHCS. Materials were thoroughly characterized using electron microscopy before being tested under Fischer‐Tropsch conditions at 220 ° C and 10 bar. Results and Discussion Scanning electron microscopy (SEM) analysis of the silica template and hollow carbon spheres gave respective average sizes of 340 nm and 290 nm, thus showing that the silica spheres shrunk as they were heated up to 900 ° C before the carbonization process (Fig 1(b,c) and Fig 2 (a,b)). The resulting hollow carbon spheres retained their spherical nature hence showing no significant breakage of the MHCS. Transmission electron microscopy (TEM) analysis of the materials showed that indeed the spheres were hollow and they had Ru nanoparticles with an average size of 4.1 nm embedded on its walls (Fig 1(e) and Fig 2 (c)). The loaded Co nanoparticles had an average particles size of approximately 5.9 nm on all three catalysts (Fig 1(f) and Fig 2 (d)). MHCS show a distinct roughness under TEM imaging suggesting high porosity of the materials which is necessary to allow reactants to access the encapsulated Ru nanoparticles. TEM tilting over a single axis proved that all the Ru nanoparticles are encapsulated inside the MHCS. Loading of Co nanoparticles outside the MHCS allowed for decoupling of the spillover effects from those that require direct Ru and Co direct contact. Electron Probe Micro‐Analysis (EPMA) large area mapping analysis proved that the metal nanoparticles are well dispersed on the MHCS and thus was ideal materials to study the spillover process (Fig 3). The Fischer‐Tropsch catalytic reaction of the three catalysts was compared and gave a Co time yield in terms of carbon monoxide and hydrogen conversion to hydrocarbons as follows; CoRu/MHCS > Ru@MHCS@Co Co/MHCS. Electron microscopy has therefore helped in following the preparation of a functional material where the promoter effects of Ru using MHCS could be evaluated. I was also observed that a close proximity of Ru and Co nanoparticles was vital for an improved catalytic performance when compared to the case where the Ru and Co nanoparticles were separated by a potential hydrogen transporting material.

Highly dispersed and ultra-small Ru nanoparticles deposited on silica support as highly active and stable catalyst for biphenyl hydrogenation

Tuning the selectivity of phenol hydrogenation using Pd, Rh and Ru nanoparticles supported on ceria- and titania-modified silicas

Chitosan as capping agent in a robust one-pot procedure for a magnetic catalyst synthesis

This article presents studies on the precipitation of Pt, Pd, Rh, and Ru nanoparticles (NPs) from model and real multicomponent solutions using sodium borohydride, ascorbic acid, sodium formate, and formic acid as reducing agents and polyvinylpyrrolidone as a stabilizing agent. As was expected, apart from PGMs, non-precious metals were coprecipitated. The influence of the addition of non-precious metal ions into the feed solution on the precipitation yield and catalytic properties of the obtained precipitates was studied. A strong reducing agent, NaBH4 precipitates Pt, Pd, Rh, Fe and Cu NPs in most cases with an efficiency greater than 80% from three- and four-component model solutions. The morphology of the PGMs nanoparticles was analyzed via SEM-EDS and TEM. The size of a single nanoparticle of each precipitated metal was not larger than 5 nm. The catalytic properties of the obtained nanomaterials were confirmed via the reaction of the reduction of 4-nitrophenol (NPh) to 4-aminophenol (NAf). Nanocatalysts containing Pt/Pd/Fe NPs obtained from a real solution (produced as a result of the leaching of spent automotive catalysts) showed high catalytic activity (86% NPh conversion after 30 min of reaction at pH 11 with 3 mg of the nanocatalyst).

Transition-metal nanoparticles (NPs) catalysts supported on solid material represent one of the most important subjects in organic synthesis due to their reliable carbon-carbon or carbon-heteroatom bond-forming cross-coupling reactions. Therefore methodologically and conceptually novel immobilization methods for nonprecious transition-metal NPs are currently required for the development of organic, inorganic, green, materials, and medicinal chemistry. We discovered a self-assembled Au-supported Pd NPs catalyst (SAPd(0)) and applied it as a catalyst to Suzuki-Miyaura coupling, Buchwald-Hartwig reaction, Carbon(sp2 and sp3)-Hydrogen bond functionalization, double carbonylation, removal of the allyl protecting groups of allyl esters, and redox switching. SAPd(0) comprises approximately 10 layers of self-assembled Pd(0) NPs, whose size is less than 5 nm on the surface of a sulfur-modified Au. The Pd NPs are wrapped in a sulfated p-xylene polymer matrix. We thought that the self-assembled Au-supported Pd NPs could be made by in situ metal NP and nanospace simultaneous organization (PSSO). This methodology involves 4 kinds of simultaneous procedures: i) reduction of a higher valence metal salt, ii) growth of metal NPs with appropriate size, iii) growth of a matrix with appropriate pores, and iv) wrapping of the metal NPs by matrix nanopores. This methodology is different from previously reported metal NPs-immobilizing methods, which use solid supports with preformed pores or coordination sites. We also applied the in situ PSSO method to prepare various immobilized transition-metal NPs, including base metals. For example, the in situ PSSO method can be applicable to easily prepare Ni, Ru, and Fe NPs with good recyclability and low metal leaching for use in organic synthesis.

Nanometer-thick defective graphene films decorated with oriented ruthenium nanoparticles. Higher activity of 101 vs 002 plane for silane-alcohol coupling and hydrogen transfer reduction

A strategy of Co doping in MgO to significantly improve the performance of solar-driven thermocatalytic CO2 reduction on Ru/Co-MgO

Atomic layer deposition (ALD) of Al2O3 using trimethylaluminum (TMA) and water on Pd nanoparticles (NPs) was studied by combining in situ quartz crystal microbalance (QCM) measurements, in situ quadrupole mass spectrometry (QMS), and transmission electron microscopy (TEM) with density functional theory (DFT) calculations. TEM images of the ALD Al2O3 overcoated Pd showed conformal Al2O3 films on the Pd NPs as expected for ALD. However, hydrogen detected by in situ QMS during the water pulses suggested that the ALD Al2O3 films on the Pd NPs were porous rather than being continuous coatings. Additional in situ QCM and QMS measurements indicated that Al2O3 ALD on Pd NPs proceeds by a self-poisoning, self-cleaning process. To evaluate this possibility, DFT calculations were performed on Pd(111) and Pd(211) as idealized Pd NP surfaces. These calculations determined that the TMA and water reactions are thermodynamically favored on the stepped Pd(211) surface, consistent with previous observations. Furthermore, the DFT studies identified methylaluminum (AlCH3*, where the asterisk designates a surface species) as the most stable intermediate on Pd surfaces following the TMA exposures, and that AlCH3* transforms into Al(OH)3* species during the subsequent water pulse. The gas phase products observed using in situ QMS support this TMA dissociation/hydration mechanism. Taken together, the DFT and experimental results suggest a process in which the Pd surface becomes poisoned by adsorbed CH3* species during the TMA exposures that prevent the formation of a complete monolayer of adsorbed Al species. During the subsequent H2O exposures, the Pd surface is cleaned of CH3* species, and the net result is a porous Al2O3 film. This porous structure can retain the catalytic activity of the Pd NPs by providing reagent gases with access to the Pd surface sites, suggesting a promising route to stabilize active Pd catalysts.

Ru single atoms and nanoparticles immobilized on hierarchically porous carbon for robust dual-pH hydrogen evolution.

Highly secretory expression of recombinant cowpea chlorotic mottle virus capsid proteins in Pichia pastoris and in-vitro encapsulation of ruthenium nanoparticles for catalysis

The synthesis and magnetic behavior of matrix-supported Pd and PdO nanoparticles (NPs) are described. Mesoporous silica with hexagonal columnal packing is selected as a template, and the impregnation method with thermal annealing is used to obtain supported Pd and PdO NPs. The heating rate and the annealing conditions determine the particle size and the phase of the NPs, with a fast heating rate of 30 °C/min producing the largest supported Pd NPs. Unusual magnetic behaviors are observed. (1) Contrary to the general belief that smaller Pd NPs or cluster size particles have higher magnetization, matrix-supported Pd NPs in this study maintain the highest magnetization with room temperature ferromagnetism when the size is the largest. (2) Twin boundaries along with stacking faults are more pronounced in these large Pd NPs and are believed to be the reason for this high magnetization. Similarly, supported PdO NPs were prepared under air conditions with different heating rates. Their phase is tetragonal (P42/mmc) with cell parameters of a = 3.050 Å and c = 5.344 Å, which are slightly larger than in the bulk phase (a = 3.03 Å, c = 5.33 Å). Faster heating rate of 30 °C/min also produces larger particles and larger magnetic hysteresis loop, although magnetization is smaller and few twin boundaries are observed compared to the supported metallic Pd NPs.