1,720,977 research outputs found
Advances in Catalytic Routes for the Homogeneous Green Conversion of the Bio-Based Platform 5-Hydroxymethylfurfural
Full text link5-Hydroxymethylfufural (HMF) is an intriguing platform molecule that can be obtained from biomasses and that can lead to the production of a wide range of products, intermediates, or monomers. The presence of different moieties in HMF (hydroxy, aldehyde, furan ring) allows to carry out different transformations such as selective oxidations and hydrogenations, reductive aminations, etherifications, decarbonylations, and acetalizations. This is a great chance in a biorefinery perspective but requires the development of active and highly selective catalysts. In this view, homogeneous catalysis can lead to efficient conversion of HMF at mild reaction conditions. This Review discussed the recent achievements in homogeneous catalysts development and application to HMF transformations. The effects of metal nature, ligands, solvents, and reaction conditions were reported and critically reviewed. Current issues and future chances have been presented to drive future studies toward more efficient and scalable processes
Chemical recycling of waste polystyrene by thermo-catalytic pyrolysis: A description for different feedstocks, catalysts and operation modes
Full text linkChemical recycling by thermo-catalytic pyrolysis/degradation offers the possibility of converting waste plastics into their original monomers or other valuable chemicals which can be used as feedstocks in chemical and petrochemical industries. Plastic wastes of polystyrene (PS) based materials can be a good source of styrene as well as mono-aromatic (BTEX: benzene, toluene, ethylbenzene, xylenes) compounds. The selectivity of pyrolysis products can be tuned by choosing the right catalyst as well as appropriate operating conditions/operation modes. In this regard, the focus of the present work was to perform thermo-catalytic pyrolysis of different waste polystyrene (WPS) feedstocks over acid and base catalysts employed in ex-situ and in-situ modes. The main goal was to compare the compositions of pyrolysis products obtained by changing feedstocks, catalysts and operation modes. A further goal was to discuss the suitability of the catalysts employed for the enhanced recovery of desired products from WPS pyrolysis. It was demonstrated that expanded polystyrene gives very similar product distribution as compared to virgin PS, both giving high styrene content. Likewise, hard PS-based random packing materials produce similar results as compared to high impact polystyrene (HIPS). Moreover, it was shown that solid base catalysts influence the composition of the pyrolysis products only slightly as compared to thermolysis. Solid acid catalyst however, showed significant impact on the composition of the pyrolysis products as compared to non-catalytic pyrolysis. These results may provide new insights for the chemical recycling of plastic wastes
Pure H2 production by methane oxy-reforming over Rh-Mg-Al hydrotalcite-derived catalysts coupled with a Pd membrane
No full textRh-Mg-Al hydrotalcites were synthesized by coprecipitation, then calcined and reduced to obtain catalysts active in the oxy-reforming of methane. In particular, it was shown that an increased activity can be obtained by reducing the Mg/Al ratio or increasing the Rh amount. In addition, the influence of pellet dimension and catalyst amount at same contact time was demonstrated to be negligible thanks to the characteristics of oxy-reforming which allows to work at low contact times without a sharp temperature rise. Moreover, a newly developed thermal treatment of the synthesized hydrotalcite was able to provide an active catalyst with an increased amount of reduced Rh over its surface, which provided very good performances. Finally, a hydrogen-selective Pd-membrane was integrated after the oxy-reforming and was able to separate H2 from the outlet mixture providing pure hydrogen in different conditions with high recoveries
Methane oxy-reforming coupled with a water gas shift membrane reactor for pure hydrogen production
No full textSolar-driven valorization of glycerol towards production of chemicals and hydrogen
Full text linkReverse microemulsion-based synthesis was successfully applied to the preparation of nanosized TiO2 particles in anatase and rutile crystalline phases. The resulted nano-oxides were found to have smaller average crystalline size, higher surface area and narrower band gap than commercial TiO2 samples, P25 and DT-51. All the TiO2 materials were used as supports for platinum nanoparticles prepared by incipient wetness impregnation and deposition-precipitation methods. The photo-catalytic activities of these materials were compared in the reaction of glycerol photo-reforming in aqueous media using simulated solar light. The results showed that different crystalline phases of titania have different effects on hydrogen production and selectivity of intermediate products. Anatase was found to be more selective towards glyceraldehyde, while the presence of rutile promoted a more selective reaction towards glycolaldehyde. Rutile also exhibited a higher productivity of hydrogen compared to anatase
Freeze cast porous membrane catalyst for hydrogen production via oxy-reforming
Full text linkIn this work, porous catalytic membrane with tailored microstructure has been developed for the production of hydrogen from the oxy-reforming process. Porous catalytic membranes have been produced by freeze-casting of ceria-based powders using camphene as solvent. The process parameters have been optimized in terms of type and amount of dispersant to obtain homogeneous and stable ceramic suspension suitable for the process, while the freezing temperature was chosen on the basis of the microstructure and porosity of the final samples. The obtained freeze cast sample produced showed very high levels of porosity (≈ 80%) and good gas permeability (1.0 × 10−11 m2). The ceria-based porous structure produced was finally evaluated as catalyst in high temperature oxy-reforming reaction for hydrogen production from methane showing high methane conversions (up to 90%) and hydrogen production. The use of a unique catalytic membrane other than pelleted catalysts allowed the obtaining of smooth thermal profiles without the evidence of endothermic or exothermic peaks
Microemulsion Derived Titania Nanospheres: An Improved Pt Supported Catalyst for Glycerol Aqueous Phase Reforming
Full text linkGlycerol aqueous phase reforming (APR) produces hydrogen and interesting compounds at relatively mild temperatures. Among APR catalysts investigated in literature, little attention has been given to Pt supported on TiO2. Therefore, herein we propose an innovative titania support which can be obtained through an optimized microemulsion technique. This procedure provided high surface area titania nanospheres, with a peculiar high density of weak acidic sites. The material was tested in the catalytic glycerol APR after Pt deposition. A mechanism hypothesis was drawn, which evidenced the pathways giving the main products. When compared with a commercial TiO2 support, the synthetized titania provided higher hydrogen selectivity and glycerol conversion thanks to improved catalytic activity and ability to prompt consecutive dehydrogenation reactions. This was correlated to an enhanced cooperation between Pt nanoparticles and the acid sites of the support
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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