CO Methanation over NiO-CeO2 Mixed-Oxide Catalysts Prepared by a Modified Co-Precipitation Method: Effect of the Preparation pH on the Catalytic Performance

In this study, a series of NiO-CeO2 mixed-oxide catalysts have been prepared by a modified co-precipitation method similar to the one used for the synthesis of hydrotalcites. The syntheses were carried out at different pH values (8, 9 and 10), in order to determine the influence of this synthetic variable on the properties of the obtained materials. These materials were characterized by using different techniques, such as TGA, XRD, ICP, N-2 adsorption-desorption isotherms, H-2 temperature-programmed reduction (H-2-TPR), and electron microscopy, including high-angle annular dark-field transmission electron microscopy (HAADF-TEM) and EDS. The characterization results revealed the influence of the preparation method, in general, and of the pH value, in particular, on the textural properties of the oxides, as well as on the dispersion of the Ni species. The catalyst prepared at a higher pH value (pH = 10) was the one that exhibited better behavior in the CO methanation reaction (almost 100% CO conversion at 235 degrees C), which is attributed to the achievement, under these synthetic conditions, of a combination of properties (metal dispersion, specific surface area, porosity) more suitable for the reaction

Reactivity of Vanadium Nanoparticles with Oxygen and Tungsten

A mechanistic study was carried out on the optimal methods of fabrication of products containing higher loads of thermochromic VO2(M1) fabricated by thermal treatments of V nanoparticles in air, that, once achieved, are more stable than other commercial products upon natural aging or reiterated reheating. At the best temperatures for single runs, 55% of VO2 can be attained by the reactions of a limited number of the species initially formed in a process, that, if not stopped, can degrade the product by solid state reactions of oxidations and reductions without O-2 consumption. This fact supports the use of two-step treatments at lower temperatures and faster cooling rates that reach 65% of VO2; such reactions should, ideally, take place in the 550-625 degrees C temperature range. The impregnation of V with a tungstate salt is an ideal and simple doping platform that can decrease the energy of activation of the 2-cycle process, allowing higher yields and enthalpies of transformation (71% of VO2, 26 J/g) than undoped counterparts or trademarks. A good balance is reached for 1% at. of W, with a reduction in T-c of 20 degrees C not significantly resenting the enthalpy of the reversible metal-to-insulator transition. For higher W amounts, the appearance of tetragonal VO2, and W alloyed V3O7 and V2O5, decrease the fractions of increasingly and effectively doped M1-VO2 achieved till 2% of W, a concentration for which T-c attains the stimulating values of 35 degrees C on heating and 25 degrees C on cooling

Unraveling the nature of active sites onto copper/ceria-zirconia catalysts for low temperature CO oxidation

The aim of this research is an attempt to shed some light on the understanding of the nature of the active sites and the generated synergies in the copper/ceria-zirconia formulations for low temperature CO oxidation by means of the creation of copper entities with different physico-chemical nature. For this reason, several CuOx/ceria-zirconia catalysts, with different Cu contents and different methods to incorporate copper species, were synthesized. Focus was specially put in this case trying to link the results of CO oxidation catalytic tests with the CO-temperature programmed reduction profiles/approximate estimations and selected characterization parameters in order to find out correlations among catalysts' properties/reducibility and catalytic behaviors, especially those corresponding to the nature and roles of the different CuOx species in contact with ceria-based support on catalytic activity. Results reveal a significant improvement in CO conversion compared to the ceria-zirconia support by adding a small amount of copper loading (as low as 0.5 %), emphasizing the paramount role of copper incorporated by the method of IWI. From 0.5 up to 2% of copper loading, an interesting increase gradual trend in activity and reducibility can be noted. It should be mentioned that all the catalysts obtained by this procedure are more catalytically active towards CO oxidation than 1%Pt/Al2O3 at low temperatures (T < 130 degrees C). CO-TPR results show that the reducibility of these catalysts is in line with their CO oxidation activity. The method of preparation has been revealed as a critical variable in the catalytic performance, and quite similar catalytic activities can be reached from different synthesis methods and different copper contents, due to the similar nature and type of CuOx species generated over the catalysts' surface, identified by the CO-TPR profiles and the rest of characterization data. Finally, IWI method seems to be the best one among those tested, thus combining superior areas of both alpha and beta contributions assigned on CO-TPR profiles, which seem to be critical in the interpretation of the catalytic behaviors

A Novel Route for the Easy Production of Thermochromic VO₂ Nanoparticles

In this work, a simple, fast and dry method for the fabrication of a thermochromic product with a high load of VO2 (M1) consisting of the controlled heat treatment of pure vanadium nanoparticles in air is presented. After a complete design of experiments, it is concluded that the most direct way to attain the maximum transformation of V into VO2 (M1) consists of one cycle with a fast heating ramp of 42°Cs-1 , followed by keeping 700°C for 530-600 seconds, and a subsequent cooling at 0.05°Cs-1 . Careful examination of these results lead to a second optimum, even more suitable for industrial production (quicker and less energy-intensive because of its lower temperatures and shorter times), consisting of subjecting V to two consecutive cycles of temperatures and times (625°C for 5 minutes) with similar preheating (42°Cs-1 ) but a much faster postcooling ( 8°Cs-1 ). These green reactions only use the power for heating a tube open to atmosphere and a vanadium precursor; without assistance of reactive gases or catalysts, and no special vacuum or pressure requirements. The best products present similar thermochromic properties but higher thermal stability than commercial VO2 particles. These methods can be combined with VO2 doping.A. J. Santos would like to thank the IMEYMAT Institute and the Spanish Ministerio de Educación y Cultura for the concessions of grants (ICARO-173873 and FPU16-04386). University of Cádiz and IMEYMAT are also agreed by financing the mutual facilities available at the UCA R&D Central Services (SC-ICYT), the UCA project references “PUENTE PR2020-003” and “OTRI AT2019/ 032”, and the IMEYMAT projects “PLP2019120-3” and “PLP2021120-1”. Additional support was given by the Spanish State Agency of Research through the “Retos” call (Project No. 1572, Ref. PID2020-114418RB-I00/ AEI / 10.13039/ 501100011033). The regional government of Andalusia with FEDER cofunding also participates through the projects AT-5983 Trewa 1157178 and FEDER-UCA18-10788, and the contract hiring M. Escanciano

Optimization of biogenic sulfur flocculation from an anoxic desulfurization bioreactor using response surface methodology

Elemental sulfur is an interesting byproduct obtained in the anoxic biodesulfurization of biogas. However, the colloidal properties of this biogenic elemental sulfur (S0) make its efficient recovery difficult. The present study investigated the flocculation of S0 produced in an anoxic bioreactor for biogas desulfurization using cationic (Sedifloc 40L4 C, Lizaflock 853 M), anionic (Innoflock 201) and non-ionic flocculants (NI-1009) and a coagulant (polyaluminum chloride). Cationic-type flocculants showed the highest flocculation efficiency, which led to its selection for further evaluation using the response surface methodology of the effects and interactions of its dose, stirring speed and pH on the biogenic sulfur flocculation rate. Optimum S0 flocculation conditions were observed using Lizaflock 853 M at a dose of 0.82 mg L−1, a stirring speed of 30 rpm and a pH of 8.0. A S0 flocculation rate of 97.05% was achieved for an initial concentration of 1730 mg S0 L−1. The Zeta potential of the settled sulfur particles increased after the flocculation process. © 2022 The Author(s

Copper-iron mixed oxide supported onto cordierite honeycomb as a heterogeneous catalyst in the Kharasch-Sosnovsky oxidation of cyclohexene

A copper-iron mixed oxide was deposited by the washcoating procedure over cordierite honeycomb monoliths for its use as a heterogeneous catalyst in organic synthesis processes. In particular, the prepared catalyst, characterized by techniques such as X-ray fluorescence, X-ray diffraction, SEM-EDS, laser granulometry, adherence tests, Temperature-Programmed Oxidation and Temperature-Programmed Reduction, showed an excellent yield and stability in the selective production of the allylic ester derived from the Kharasch-Sosnovsky oxidation of cyclohexene with benzoic acid. The use of a structured catalyst here proposed opens up an interesting alternative to homogeneous catalysis in the field of synthetic chemistry. © 2021 The AuthorsThe authors thank the Ministry of Economy and Competitiveness of Spain (Projects MAT2017-85-719-R , and AGL2017-88083-R ), the Junta de Andalucía ( FQM-110 and FQM-169 groups), and the Institute of Electron Microscopy and Materials (IMEYMAT) of Cadiz University (UCA) (Projects HOMOGREEN and NUPRECAT) for their financial support. They also acknowledge the SC-ICYT of the UCA for using its XRD NMR, and electron microscopy division facilities

Producing C-S-H gel by reaction between silica oligomers and portlandite: A promising approach to repair cementitious materials

Impregnation treatments are one of the alternatives to protect concrete-based building and monuments from weathering degradation. However, it is important to consider the chemical compatibility of the reaction products with the building material. The impregnation product studied here consists of a silica oligomer able to poly- merize, by a simple sol-gel process, inside the pore structure of concrete. In this work, we investigate the ability of this impregnation treatment to produce C-S-H gel in contact with cement paste. A complete characterization of the reaction products demonstrated that the silanol groups from silica oligomers react with the portlandite present in the cement paste generating a material with the chemical, structural and morphological features of C- S-H gel. Simultaneously, the 29Si NMR results indicate that the SieO units are incorporated into the existing C-S- H, increasing its chain length. These results open the way for a simple concrete structures repairing procedure. 1

Solvothermal synthesis and characterization of ytterbium/iron mixed oxide nanoparticles with potential functionalities for applications as multiplatform contrast agent in medical image techniques

A solvothermal route to prepare Glutathione capped hybrid ytterbium/iron oxide nanoparticles with potential applications as multiplatform contrast agent in medical image techniques has been developed. The influence of ytterbium/iron molar ratio used as precursor, as well as the degree of the autoclave filling on the structural and morphological characteristics of the obtained nanoparticles has been extensively studied. Although all nanoparticles present similar composition, with YbFeO3 being the majority phase, size and morphology of the as synthetized nanoparticles are highly influenced by the critical temperature and by the over -saturation reached during the solvothermal process. We have demonstrated that glutathione properly functionalizes the hybrid nanoparticles, increasing their colloidal stability and decreasing their cytotoxicity. Additionally, they show good imaging in magnetic resonance and X-ray computerized tomography, thereby indicating promising potential as a dual contrast agent. This work presents, for the first time, glutathione functionalized ytterbium/iron oxide nanoparticles with potential applications in Biomedicine.12 página