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

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

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