Base-free Oxidative Esterification of HMF over AuPd/nNiO-TiO2. When Alloying Effects and Metal-support Interactions Converge in Producing Effective and Stable Catalysts

Furan-2,5-dimethylcarboxylate (FDMC), along with ethylene glycol (EG), is the key monomer to produce (poly-(ethylene-furanoate) (PEF). Noble metal-based catalysts can convert hydroxymethyl furfural (HMF) to FDMC in methanol through liquid phase catalytic oxidative esterification. In this work, the catalytic performance of Au, Pd and AuPd NPs supported on nanosized nickel oxide (nNiO) have been evaluated under base-free conditions at 90 degrees C and 3 bar O-2. Synergistic effects between Au and Pd imparted high activity and higher yield to FDMC compared to the monometallic counterparts. The role of support was also investigated by depositing AuPd NPs on TiO2 and nNiO-TiO2. Remarkable yield to FDMC (85 % after 8 h) and high stability were observed over AuPd/ nNiO-TiO2 catalyst. This peculiar catalytic behavior could be imputed to the formation of trimetallic AuPdNi particles offering highly active interfacial sites

Direct Imaging of Radiation-Sensitive Organic Polymer-Based Nanocrystals at Sub-Ångström Resolution

Seeing the atomic configuration of single organic nanoparticles at a sub-Å spatial resolution by transmission electron microscopy has been so far prevented by the high sensitivity of soft matter to radiation damage. This difficulty is related to the need to irradiate the particle with a total dose of a few electrons/Å2, not compatible with the electron beam density necessary to search the low-contrast nanoparticle, to control its drift, finely adjust the electron-optical conditions and particle orientation, and finally acquire an effective atomic-resolution image. On the other hand, the capability to study individual pristine nanoparticles, such as proteins, active pharmaceutical ingredients, and polymers, with peculiar sensitivity to the variation in the local structure, defects, and strain, would provide advancements in many fields, including materials science, medicine, biology, and pharmacology. Here, we report the direct sub-ångström-resolution imaging at room temperature of pristine unstained crystalline polymer-based nanoparticles. This result is obtained by combining low-dose in-line electron holography and phase-contrast imaging on state-of-the-art equipment, providing an effective tool for the quantitative sub-ångström imaging of soft matter

Catalytic Decomposition of n-C-7 Asphaltenes Using Tungsten Oxides-Functionalized SiO2 Nanoparticles in Steam/Air Atmospheres

A wide range of technologies are being developed to increase oil recovery, reserves, and perform in situ upgrading of heavy crude oils. In this study, supported tungsten oxide nanoparticles were synthesized, characterized, and evaluated for adsorption and catalytic performance during wet in situ combustion (6% of steam in the air, in volumetric fraction) of n-C-7 asphaltenes. Silica nanoparticles of 30 nm in diameter were synthesized using a sol-gel methodology and functionalized with tungsten oxides, using three different concentrations and calcination temperatures: 1%, 3%, 5% (mass fraction), and 350 degrees C, 450 degrees C, and 650 degrees C, respectively. Equilibrium batch adsorption experiments were carried out at 25 celcius with model solutions of n-C-7 asphaltenes diluted in toluene at concentrations from 100 mg center dot L-1 to 2000 mg center dot L-1, and catalytic wet in situ combustion of adsorbed heavy fractions was carried out by thermogravimetric analysis coupled to FT-IR. The results showed improvements of asphaltenes decomposition by the action of the tungsten oxide nanoparticles due to the reduction in the decomposition temperature of the asphaltenes up to 120 degrees C in comparison with the system in the absence of WOX nanoparticles. Those synthesis parameters, such as temperature and impregnation dosage, play an important role in the adsorptive and catalytic activity of the materials, due to the different WOX-support interactions as were found through XPS. The mixture released during the catalyzed asphaltene decomposition in the wet air atmosphere reveals an increase in light hydrocarbons, methane, and hydrogen content. Hydrogen production was prioritized between 300 and 400 degrees C where, similarly, the reduction of CO, CH4, and the increase in CO2 content, associated with water-gas shift, and methane reforming reactions occur, respectively. The results show that these catalysts can be used either for in situ upgrading of crude oil, or any application where heavy fractions must be transformed

Developing and understanding Leaching-Resistant cobalt nanoparticles via N/P incorporation for liquid phase hydroformylation

The ultimate target in heterogeneous catalysis is the achievement of robust, resilient and highly efficient materials capable of resisting industrial reaction conditions. Pursuing that goal in liquid-phase hydroformylation poses a unique challenge due to carbon monoxide-induced metal carbonyl species formation, which is directly related to the formation of active homogeneous catalysts by metal leaching. Herein, supported heteroatomincorporated (P and N) Co nanoparticles were developed to enhance the resistance compared with bare Co nanoparticles. The samples underwent characterization using operando XPS, XAS and HR electron microscopy. Overall, P- and N-doped catalysts increased reusability and suppressed leaching. Among the studied catalysts, the one with N as a dopant, CoNx@NC, presents excellent catalytic results for a Co-based catalyst, with a 94% conversion and a selectivity to aldehydes of 80% in only 7.5 h. Even under milder conditions, this catalyst outperformed existing benchmarks in Turnover Numbers (TON) and productivity. In addition, computational simulations provided atomistic insights, shedding light on the remarkable resistance of small Co clusters interacting with N-doped carbon patches

Synthesis and Structural Characterization of Branched Bimetallic AuPd Nanoparticles with a Highly Tunable Optical Response

Bimetallic nanostructures composed of gold (Au) and palladium (Pd) have garnered increased interest for their applications in heterogeneous catalysis. This study reports a simple strategy for manufacturing Au@Pd bimetallic branched nanoparticles (NPs), which offer a tunable optical response, using polyallylamine-stabilized branched AuNPs as template cores for Pd overgrowth. The palladium content can be altered by manipulating the concentration of PdCl4 2− and ascorbic acid (AA) that are injected, which permit an overgrowth of the Pd shell up to ca. 2 nm thick. The homogeneous distribution of Pd at the surfaces of Au NPs can be carried out regardless of their size or branching degree, which allows for an adjustment of the plasmon response in the near-infrared (NIR) spectral range. As a proof of concept, the nanoenzymatic activity of pure gold and gold−palladium NPs was compared, exploring their peroxidase-like activity in the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB). The bimetallic AuPd NPs demonstrate an increase in the catalytic properties attributed to the presence of palladium at the surface of gold

Determining the Role of Fe-Doping on Promoting the Thermochemical Energy Storage Performance of (Mn1-xFex)(3)O-4 Spinels

Mn oxides are promising materials for thermochemical heat store, but slow reoxidation of Mn3O4 to Mn2O3 limits efficiency. In contrast, (Mn1-xFex)(3)O-4 oxides show an enhanced transformation rate, but fundamental understanding of the role played by Fe cations is lacking. Here, nanoscale characterization of Fe-doped Mn oxides is performed to elucidate how Fe incorporation influences solid-state transformations. X-ray diffraction reveals the presence of two distinct spinel phases, cubic jacobsite and tetragonal hausmannite for samples with more than 10% of Fe. Chemical mapping exposes wide variation of Fe content between grains, but an even distribution within crystallites. Due to the similarities of spinels structures, high-resolution scanning transmission electron microscopy cannot discriminate unambiguously between them, but Fe-enriched crystallites likely correspond to jacobsite. In situ X-ray absorption spectroscopy confirms that increasing Fe content up to 20% boosts the reoxidation rate, leading to the transformation of Mn2+ in the spinel phase to Mn3+ in bixbyite. Extended X-ray absorption fine structure shows that Fe-O length is larger than Mn-O, but both electron energy loss spectroscopy and X-ray absorption near edge structure indicate that iron is always present as Fe3+ in octahedral sites. These structural modifications may facilitate ionic diffusion during bixbyite formation.The authors thank the financial support from "Ramon Areces" Foundation (project SOLARKITE), Comunidad de Madrid and European Structural Funds (project ACES2030 P2018/EMT-4319), and University of Cadiz and European Structural Funds (project FEDER-UCA18-107139). A.J.C. thanks the financial support by Juan de la Cierva Formacion Program (MICINN), grant FJCI-2017-33967. The authors acknowledge ALBA-CELLS Synchrotron facility for granting beamtime at CLAESS (experiment 2016021666-2) and Electron Microscopy division located in the Servicios Centrales de Investigacion Cientifica y Tecnologica (SC-ICYT) of the University of Cadiz. Assistance of Dr. Laura Simonelli during the XAS measurements in ALBA is fully appreciated

Size, nanostructure, and composition dependence of bimetallic Au–Pd supported on ceria–zirconia mixed oxide catalysts for selective oxidation of benzyl alcohol

A bimetallic Au–Pd catalyst supported on ceria–zirconia with Au:Pd molar ratio 0.8 has been synthesized using a simultaneous deposition–precipitation method and oxidized at 250, 450, and 700 °C in order to modify its particle size, nanostructure, and composition. Combined X-ray energy dispersive spectroscopy (XEDS)and X-ray photoelectron spectroscopy (XPS)analysis clearly evidence that the bimetallic Au–Pd catalyst oxidized at 250 °C is made up of a mixture of monometallic Au and Pd and bimetallic Au–Pd nanoparticles with Au:Pd ratios varying over a wide range. Increasing oxidation temperature leads to a stronger interaction between Au and Pd. Meanwhile, a slight increase of particle size and a narrowing of the Au:Pd ratio in the bimetallic nanoparticles take place. Compared with titania and activated carbon supports, the resistance against sintering at high temperatures of Au–Pd metal particles supported on ceria–zirconia is proven to be higher. A synergistic effect has been observed for selective oxidation of benzyl alcohol on these catalysts. The catalytic activity decreases only slightly after oxidation at 450 °C. However, oxidation at 700 °C results in much lower catalytic activity. Migration of Pd onto Au particles during oxidation of benzyl alcohol enhances the catalytic activity of a physical mixture of monometallic Au and Pd supported on ceria–zirconia catalysts. This fact, jointly with an analysis of the intrinsic activity, reveals the influence of the actual nature of Au–Pd interactions in the bimetallic particles, which points to higher activity of Au@Pd or AuPd@Pd nanostructures on ceria–zirconia support