Formation and growth characteristics of nanostructured carbon films on nascent Ag clusters during room-temperature electrochemical CO2 reduction

Synthesis of carbon nanostructures at room temperature and under atmospheric pressure is challenging but it can provide significant impact on the development of many future advanced technologies. Here, the formation and growth characteristics of nanostructured carbon films on nascent Ag clusters during room-temperature electrochemical CO(2) reduction reactions (CO(2)RR) are demonstrated. Under a ternary electrolyte system containing [BMIm](+)[BF(4)](−), propylene carbonate, and water, a mixture of sp(2)/sp(3) carbon allotropes were grown on the facets of Ag nanocrystals as building blocks. We show that (i) upon sufficient energy supplied by an electric field, (ii) the presence of negatively charged nascent Ag clusters, and (iii) as a function of how far the C–C coupling reaction of CO(2)RR (10–390 min) has advanced, the growth of nanostructured carbon can be divided into three stages: Stage 1: sp(3)-rich carbon and diamond seed formation; stage 2: diamond growth and diamond–graphite transformation; and stage 3: amorphous carbon formation. The conversion of CO(2) and high selectivity for the solid carbon products (>95%) were maintained during the full CO(2)RR reaction length of 390 min. The results enable further design of the room-temperature production of nanostructured carbon allotropes and/or the corresponding metal-composites by a viable negative CO(2) emission technology

Synthesis of Cu/TiO2 catalysts by reactive magnetron sputtering deposition and its application for photocatalytic reduction of CO2 and H2O to CH4

© 2019 In the present work, a series of Cu/TiO2 catalysts were successfully synthesized by using pulsed direct current (DC) reactive magnetron sputtering of Cu targets under Ar atmosphere onto various TiO2 supports. The physiochemical properties of the catalysts were characterized by using inductive coupled plasma spectroscopy (ICP), X-ray diffraction (XRD), UV–Vis spectroscopy, N2 physisorption, transmission electron microscopy (TEM), PL spectroscopy, and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of all the catalysts were studied via the photocatalytic reduction of CO2 and H2O to CH4 under UV light irradiation. The Cu/TiO2 catalysts exhibited higher photocatalytic activity than the uncoated TiO2 supports and the ones made using an impregnation technique. The electron trapping of copper species, which prolonged the electron-hole recombination process, promoted photocatalytic activity of the Cu-doped catalysts. Moreover, the specific morphologies of the Cu species deposited on TiO2 supports and the smaller change of bandgap energy of the sputter coated catalysts also resulted in an improvement of photocatalytic activity under UV light irradiation

Effect of Dispersion of the Active Phase on the Activity and Coke Formation over WO3/SiO2 Catalysts in the Metathesis of Ethylene and 2-Butene

SSCI-VIDE+ATARI+NPO:FCAInternational audienceWO3/SiO2 catalysts with various tungsten loadings were prepared by the incipient wetness impregnation method and studied in the metathesis of ethylene and trans-2-butene as feed to produce propylene. Two different calcination methods were used to modify the dispersion of the tungsten active phase. The catalysts were characterized by X-ray diffraction, transmission electron microscopy, nitrogen physisorption, ion-exchange titration, FT-Raman, ammonia temperature programmed desorption and temperature programmed oxidation. Better dispersion is obtained from low heating rate calcination. The dispersion of tungsten showed a direct effect on coke formation and was the key factor to improve the stability of the catalysts

Effect of reduction temperature on the characteristics and catalytic properties of TiO2 supported AuPd alloy particles prepared by one-step flame spray pyrolysis in the selective hydrogenation of 1-heptyne

SSCI-VIDE+ATARI+BPO:NSP:EEHInternational audienceThe bimetallic flame spray-synthesized AuPd/TiO2 catalysts (Au:Pd weight ratio 1:1) were reduced for 2 h under H-2 at two different temperatures (40 degrees C and 500 degrees C) and tested in the liquid phase selective hydrogenation of 1-heptyne under mild conditions (30 degrees C and 4 bar H-2). Based on TEM-EDX analysis of individual nanoparticles, reduction at 500 degrees C tends to homogenize the composition of the individual AuPd nanoparticles without significant changes of their average particle size and bulk composition. Higher reaction rate (245 mu mol s(-1) g cat.(-1)) was obtained on the AuPd/TiO2 R40 than on the AuPd/TiO2 R500 (223 mu mol s(-1) g cat.(-1)). Upon reduction at 500 degrees C, the bimetallic AuPd/TiO2 exhibited a similar degree of the strong-metal support interaction (SMSI) effect as the monometallic one. As revealed by XPS results, the ratios of Pd/Ti on both catalysts decreased by ca. 23%, due probably to the migration of TiOx species onto the metals. The highest yield of 1-heptene (similar to 93%) was obtained over the bimetallic AuPd/TiO2 reduced at 40 degrees C in 20 min reaction time under the reaction conditions used. The high temperature reduction is unnecessary for the improvement of catalyst performances when using supported bimetallic AuPd catalysts. (C) 2015 Elsevier B.V. All rights reserved

Nanometer WOx species evidenced by HRTEM/EDX in WO3/SiO2 catalysts for the metathesis reaction

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Influence of surface Sn species and hydrogen interactions on the OH group formation over spherical silica-supported tin oxide catalysts

Silica-supported tin oxide catalysts are currently used in chemical processes involving hydrogen. A deeper understanding of the interactions of molecular hydrogen with the catalyst surface is crucial, to gain insights into structure-activity relationships that control the catalytic performance. This work aims to explore the influence of Sn species on silica-supported tin oxide catalysts and in particular the role of OH groups formed during hydrogen exposure. Tin oxide supported on spherical silica nanoparticle (SSP) catalysts was investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The catalysts were synthesized using two different methods, incipient wetness impregnation (IWI-Sn) and incorporation (Inc-Sn) of Sn species to the SSP support with the sol-gel method. In situ DRIFTS showed that new OH groups on the silica surface are formed over SSP-supported tin oxide catalysts during the hydrogen exposure. The Sn-O-Si species play a key role in the formation of new OH groups on the silica surface over the catalysts. These Sn-O-Si species were predominant on the Inc-Sn catalysts, while the IWI-Sn catalyst presented various types of Sn species. Moreover, the Sn-O-Si species increased with the increase of Sn contents in both samples. The analytical results indicate that the newly generated OH groups appeared mostly on the silica surface surrounding the Sn-O-Si species. This journal i

Bimetallic Pd-Sn and Pd-Ga Catalysts for the Hydrogenation of 1,3-Butadiene

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