Gold nanoparticles onto cerium oxycarbonate as highly efficient catalyst for aerobic allyl alcohol oxidation

Abstract Au nanoparticles, generated by the metal vapor synthesis technique, were supported onto cerium oxycarbonate monohydrate (Ce2O(CO3)2·H2O) giving Au@Ce2O(CO3)2·H2O. The obtained heterogeneous catalyst was used in the aerobic allyl alcohol oxidation reaction performed in toluene, showing a notably higher catalytic substrate conversion and isomerization activity compared to Au onto ceria, which is the reference catalyst for this type of catalysis. Results originating from catalytic recycling experiments and PXRD, HRTEM and XPS measurements carried out on recovered Au@Ce2O(CO3)2·H2O, confirmed the stability of the catalyst under aerobic oxidation reaction conditions and hence its recyclability, without the need of a regeneration step

Discovering indium as hydrogen production booster for a Cu/SiO2 catalyst in steam reforming of methanol

Abstract We report on the use of In as an effective H2 production promoter in a Cu/SiO2 catalyst for the steam reforming of methanol. To date, In promotion has been limited to noble metals because of its tendency to "bury" other metals thus compromising the catalytic activity. Here, we prepared a silica-supported Cu-In catalyst via a urea-assisted co-precipitation method that showed a higher H2 productivity compared to the monometallic catalyst and a remarkable H2/CO2 molar ratio of almost 3 at 220 °C. Through XPS, XRPD and HRTEM-EDX along with H2- and CO-TPR, H2O-TPD, and N2O titrations, supported by computational modeling, we attributed such superior performances to an easier H2O activation due to improved electronic properties of the Cu phase, that is, its lower oxidation state via electron density transfer from the InOx buffer phase as a 1D "necklace" structures crucially mediating the interaction of small Cu nanoparticles (2.6 nm) and silica

Photoelectrochemical abatement of arsenic in water by hematite photoelectrodes

Arsenic is considered as one of the major issues among drinkable water pollutants because of its widespread distribution and its low acceptable limits. The most widely used removal technology involves arsenic adsorption on iron oxides, but this process is more effective for As(V). Since in groundwater arsenic is usually present as As(III), a preliminary oxidation treatment is often required to get high abatement yields. Moreover, despite it is a cheap and effective technology, adsorption generates a contaminated bed that must be disposed as toxic waste or regenerated by expensive techniques. Aiming at solving such problems, we are developing an alternative process involving a one-pot photoelectrochemical in situ oxidation and adsorption. Hematite nanostructured photoelectrodes showed promising performances by achieving almost complete abatement of arsenic from aqueous solutions under simulated solar light irradiation, in the view of economic and environmental sustainable application

Titanium Dioxide Photocatalysis

Dating from the seminal work of Fujishima et al. [...

Design and Use of Nanostructured Single-Site Heterogeneous Catalysts for the Selective Transformation of Fine Chemicals

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Surfactant-controlled composition and crystal structure of manganese(II) sulfide nanocrystals prepared by solvothermal synthesis

We investigated how the outcome of the solvothermal synthesis of manganese(II) sulfide (MnS) nanocrystals (NCs) is affected by the type and amount of long chain surfactant present in the reaction mixture. Prompted by a previous observation that a larger than stoichiometric amount of sulfur is required [Puglisi, A.; Mondini, S.; Cenedese, S.; Ferretti, A. M.; Santo, N.; Ponti A. Chem. Mater. 2010, 22, 2804–2813], we carried out a wide set of reactions using Mn(II) carboxylates and Mn2(CO)10 as precursors with varying amounts of sulfur and carboxylic acid. MnS NCs were obtained provided that the S/Mn ratio was larger than the L/Mn ratio, otherwise MnO NCs were produced. Since MnS can crystallize in three distinct phases (rock salt α-MnS, zincblende β-MnS, and wurtzite γ-MnS), we also investigated whether the surfactant affected the NC polymorphism. We found that MnS polymorphism can be controlled by appropriate selection of the surfactant. γ-MnS nanocrystals formed when a 1:2 mixture of long chain carboxylic acid and amine was used, irrespective of the presence of carboxylic acid as a free surfactant or ligand in the metal precursor. When we used a single surfactant (carboxylic acid, alcohol, thiol, amine), α-MnS nanocrystals were obtained. The peculiar role of the amine seems to be related to its basicity. The nanocrystals were characterized by TEM and electron diffraction; ATR-FTIR spectroscopy provided information about the surfactants adsorbed on the NCs

Methane Reforming Processes: Advances on Mono- and Bimetallic Ni-Based Catalysts Supported on Mg-Al Mixed Oxides

Ni-based catalysts supported on Mg-Al mixed oxides (Mg(Al)O) have been intensively investigated as catalysts for CH4 reforming processes (i.e., steam reforming (SMR) and dry reforming (DRM)), which are pivotal actors in the expanding H2 economy. In this review, we provide for the first time an in-depth analysis of homo- and bimetallic Ni-based catalysts supported on Mg(Al)O supports reported to date in the literature and used for SMR and DRM processes. Particular attention is devoted to the role of the synthesis protocols on the structural and morphological properties of the final catalytic materials, which are directly related to their catalytic performance. It turns out that the addition of a small amount of a second metal to Ni (bimetallic catalysts), in some cases, is the most practicable way to improve the catalyst durability. In addition, besides more conventional approaches (i.e., impregnation and co-precipitation), other innovative synthesis methods (e.g., sol-gel, atomic layer deposition, redox reactions) and pretreatments (e.g., plasma-based treatments) have shown relevant improvements in identifying and controlling the interaction among the constituents most useful to improve the overall H2 productivity

Well-formed, size-controlled ruthenium nanoparticles active and stable for acetic acid steam reforming

Mg(Al)O supported Ru and Rh catalysts with low loading of active metal (0.5wt.%) were tested in the steam reforming (SR) of acetic acid (AA) to hydrogen rich mixtures. Two synthetic procedures were adopted to deposit metal nanoparticles on support material: conventional impregnation from metal chlorides aqueous solutions and size-controlled metal nanoparticles (SCMNPs) deposition method. SCMNP derived Ru catalysts showed good performances fully comparable to standard Rh based systems. After 20h t.o.s. at reaction temperature of 700°C, steam-to-carbon ratio of 3 and weight hourly space velocity of 6h-1, Ru catalysts showed 100% conversion and hydrogen yield higher than 70%. The presence of well formed metal nanoparticles and the residual hydrotalcite present in the support play a determinant role in limiting the deactivation by coke deposition and by nanoparticles sintering