Environmental concerns have introduced a need to remove sulfur-containing compounds from light oil. As oxidative desulfurization is conducted under very mild reaction conditions, much attention has ...recently been devoted to this process. In this contribution, the developments in selective removal of organosulfur compounds present in liquid fuels via oxidative desulfurization, including both chemical oxidation and biodesulfurization, are reviewed. At the end of each section, a brief account of the research directions needed in this field is also included. Copyright
Technological approaches which enable the effective utilization of CO2 for manufacturing value-added chemicals and fuels can help to solve environmental problems derived from large CO2 emissions ...associated with the use of fossil fuels. One of the most interesting products that can be synthesized from CO2 is methanol, since it is an industrial commodity used in several chemical products and also an efficient transportation fuel. In this review, we highlight the recent advances in the development of heterogeneous catalysts and processes for the direct hydrogenation of CO2 to methanol. The main efforts focused on the improvement of conventional Cu/ZnO based catalysts and the development of new catalytic systems targeting the specific needs for CO2 to methanol reactions (unfavourable thermodynamics, production of high amount of water and high methanol selectivity under high or full CO2 conversion). Major studies on the development of active and selective catalysts based on thermodynamics, mechanisms, nano-synthesis and catalyst design (active phase, promoters, supports, etc.) are highlighted in this review. Finally, a summary concerning future perspectives on the research and development of efficient heterogeneous catalysts for methanol synthesis from CO2 will be presented.
Pena and Fierro discuss the study of oxides and their relevance in heterogenous catalysis and surface chemistry. The broad diversity of properties that these compounds exhibit is derived from the ...fact that around 90% of the metallic natural elements of the Periodic Table are known to be stable in a perovskite-type oxide structure.
This paper addresses the options developed over the past two decades for the conversion of methane into valuable chemicals and fuels while avoiding the high energy requirements of the steam reforming ...process for producing H
2/CO mixtures. Several aspects of the approaches undertaken accordingly are briefly examined here. Each option has its own set of limitations. Nonetheless, the cost-effective separation of useful products is a common denominator across the board in these processes, with the other most important issue being the separation of oxygen from air, requiring C–H bond activation by oxygen. The widespread use of methane for producing fuels and chemicals appears to be within reach, but current economic uncertainties limit both the amount of research activity and the implementation of emerging technologies, although the extensive use of methane for the production of fuels and chemicals is expected to become a reality very soon.
Ni catalysts supported on different carriers like δ,θ-Al2O3, MgAl2O4, SiO2–Al2O3 and ZrO2–Al2O3 were prepared. The solids were characterized by chemical analysis, N2 adsorption–desorption isotherms, ...X-ray powder diffraction, UV–vis diffuse reflectance spectroscopy, temperature-programmed reduction, high-resolution transmission electron microscopy and temperature-programmed oxidation. The catalytic properties of the samples were evaluated in the reaction of reforming of methane with CO2 at 923 K. It was shown that this kind of support greatly affects the structure and catalytic performance of the catalysts. Ni catalyst supported on MgAl2O4 showed the highest activity and stability due to the presence of small well dispersed Ni particles with size of 5.1 nm. It was shown that the lowest activity of Ni catalyst supported on SiO2–Al2O3 oxide was caused by the agglomeration of nickel particles and formation of filamentous carbon under reaction conditions detected by the high resolution transmission electron microscopy.
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► Catalytic properties of Ni catalysts in dry methane reforming are studied. ► A strong interaction between NiO and MgAl2O4 exists. ► The best activity of Ni/MgAl catalyst is due to the smallest Ni size of 5.1 nm.
A series of Ni/Fe electrodes have been prepared by electrodeposition of metal salt precursors on different substrates. The surface morphology, chemical composition and electrochemical characteristics ...of these electrodes were studied by various physico-chemical techniques such as X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM). The electrochemical properties of the electrodes were examined by steady-state polarization curves. First, the influence of features such as Ni/Fe composition and type of substrate for the oxygen evolution reaction (OER) were determined by electrochemical techniques in a conventional 3-electrodes cell. The overpotential for the OER is lower for the electrodes with the higher concentrations of Ni. The electrodes with a Ni/Fe composition of 75/25 wt.% electrodeposited on steel mesh and/or 75/25 and 50/50 wt.% on nickel foam result in the most active configurations for the OER. These electrodes were further tested as anodes for alkaline water electrolysis during at least 70 h. In order to understand their activity and stability, the used electrodes were also characterized by SEM and compared to the fresh electrodes. Among the compositions and substrates examined, the Ni50Fe50-Nf electrode exhibited the lowest overpotential (2.1 V) for the OER and the higher stability as anode in an alkaline water electrolysis cell.
Adsorption of organo-sulfur compounds present in liquid fuels on metal–organic framework (MOF) compounds is an efficient alternative to the conventional hydrodesulfurization process. It has been ...demonstrated that the extent of dibenzothiophene (DBT) adsorption at temperatures close to ambient (304
K) is much higher on MOFs systems than on the benchmarked Y-type zeolite. In addition, the DBT adsorption capacity depends strongly on the MOF type as illustrated by the much higher extent of adsorption observed on the copper- (C300) and Al-containing (A100) MOF systems than on the Fe-containing (F300) MOF counterpart. With the aim to investigate the operation in consecutive cycles, the MOFs used in adsorption experiments were regenerated. In addition, the remaining S-containing compounds were identified and quantified by photoelectron spectroscopy (XPS). Examination of S2p core-level spectrum of the adsorbed S-compounds of regenerated MOFs pointed out that a fraction of these molecules become oxidized into S(VI) species.
The catalytic oxidation of methane was investigated over six catalysts with different palladium and platinum molar ratios. The catalysts were characterised by TEM, EDS, XPS, PXRD and ...temperature-programmed oxidation. The results suggest that in the bimetallic catalysts, an alloy between Pd and Pt was formed in close contact with the PdO phase, with an exception for the Pt-rich catalyst, where no PdO was observed. It was found that the molar ratio between palladium and platinum clearly influences both the activity and the stability of methane conversion. By adding small amounts of platinum into the palladium catalyst, improved activity was obtained in comparison with the monometallic palladium catalyst. However, higher amounts of platinum are required for stabilising the methane conversion. The most promising catalysts with respect to both activity and stability were Pd
67Pt
33 and Pd
50Pt
50. The platinum-rich catalyst showed very poor activity for methane conversion.
CeO
2–ZrO
2 oxides with different CeO
2 content (1–12
wt%) were prepared by the impregnation method. The effects of CeO
2 content, calcination temperature and interaction between the components on ...the structure and reductive properties of CeO
2–ZrO
2 oxides were evaluated by using different techniques such as XRD, DRS, FTIR, Raman, XPS, TGA and TPR. Spectroscopic data showed that the tetragonal phase of zirconia is preserved in all CeO
2–ZrO
2 oxides, although they retain a high number of defect sites caused by a strong interaction between zirconia and cerium oxide species. An enrichment of the zirconia surface with a fluorite structure of CeO
2 is observed for the CeO
2–ZrO
2 oxide with the highest CeO
2 content (12
wt%). The samples subjected to consecutive reduction–oxidation cycles at different temperatures showed good redox properties related to the increase of oxygen mobility. It was concluded that these CeO
2–ZrO
2 oxide systems, displaying high surface and good thermal stability, are similar to chemically mixed oxides due to the strong interaction between the zirconia carrier and deposited ceria.
The effect of CeO
2 content, calcination temperature and interaction between components on the structure and redox properties of CeO
2–ZrO
2 oxides was evaluated. At the highest CeO
2 loading (12
wt%) and after high temperature treatment of 1073
K an enrichment of the zirconia surface with a fluorite structure of CeO
2 is observed in the figure. XRD of CeO
2, ZrO
2 and CeO
2–ZrO
2 oxides with different CeO
2 content after temperature treatment at 823 (A) and 1073
K (B).
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