Relationship between bulk phase, near surface and outermost atomic layer of VPO catalysts and their catalytic performance in the oxidative dehydrogenation of ethane

A set of vanadium phosphorous oxide (VPO) catalysts, mainly consisting of (VO)₂P₂O₇, VO(PO₃)₂ or VOPO₄∙2H₂O bulk crystalline phases, has been investigated for the oxidative dehydrogenation (ODH) of ethane to ethylene, a key potential reaction for a sustainable industrial and socioeconomic development. The catalytic performance on these VPO catalysts has been explained on the basis of the main crystalline phases and the corresponding suface features found by XPS and LEISS at 400 ˚C, i.e. within the temperature range used for ODH reaction. The catalysts based on (VO)₂P₂O₇ phase presented the highest catalytic activity and productivity to ethylene. Nevertheless, the catalysts consisting of VO(PO₃)₂ structure showed higher selectivity to ethylene, reaching 90% selectivity at ca. 10% ethane conversion. To the best of our knowledge, this is the highest selectivity reported on a vanadium phosphorous oxide at similar conversions for the ethane ODH. In general, catalysts consisting of crystalline phases with vanadium present as V⁴⁺, i.e. (VO)₂P₂O₇ and VO(PO₃)₂, were found to be significantly more selective to ethylene than those containing V⁵⁺ phases. The surface analysis by XPS showed an inverse correlation between the mean oxidation state of vanadium near surface and the selectivity to ethylene. The lower averaged oxidation states of vanadium appear to be favoured by the presence of V³⁺ species near the surface, which was only found in the catalysts containing V⁴⁺ phases. Among those catalysts the one based on VO(PO₃)₂ phase shows the highest selectivity, which could be related to the most isolated scenario of V species (the lowest V content relative to P) found at the outermost surface by low energy ion scattering spectroscopy (LEISS), a "true" surface technique only sensitive to the outermost atomic layer

Enhanced NiO Dispersion on a High Surface Area Pillared Heterostructure Covered by Niobium Leads to Optimal Behaviour in the Oxidative Dehydrogenation of Ethane

This is the peer reviewed version of the following article: E. Rodríguez-Castellón, D. Delgado, A. Dejoz, I. Vázquez, S. Agouram, J. A. Cecilia, B. Solsona, J. M. López Nieto, Chem. Eur. J. 2020, 26, 9371, which has been published in final form at https://doi.org/10.1002/chem.202000832. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.[EN] A Nb-containing siliceous porous clay heterostructure (PCH) with Nb contents from 0 to 30 wt %) was prepared from a bentonite and used as support in the preparation of supported NiO catalysts with NiO loading from 15 to 80 wt %. Supports and NiO-containing catalysts were characterised by several physicochemical techniques and tested in the oxidative dehydrogenation (ODH) of ethane. The characterisation studies on Nb-containing supports showed the presence of well-anchored Nb(5+)species without the formation of Nb(2)O(5)crystals. High dispersion of nickel oxide with low crystallinity was observed for the Nb-containing PCH supports. In addition, when NiO is supported on these Nb-containing porous clays, it is more effective in the ODH of ethane (ethylene selectivity of ca. 90 %) than NiO supported on the corresponding Nb-free siliceous PCH or on Nb2O5(ethylene selectivities of ca. 30 and 60 %, respectively). Factors such as the NiO-Nb(5+)interaction, the NiO particle size and the properties of surface Ni(n+)species were shown to determine the catalytic performance.The authors would like to acknowledge the Ministerio de Ciencia, Innovacion y Universidades of Spain (CRTl2018-099668-B-C21, RTl2018-099668-B-C22 and MAT2017-84118-C2-1-R projects). Authors from ITQ also thank Project SEV-2016-0683 for supporting this research. D.D. thanks MINECO and Severo Ochoa Excellence Program for his fellowship (SVP-2014-068669).Rodríguez-Castellón, E.; Delgado-Muñoz, D.; Dejoz, A.; Vázquez, I.; Agouram, S.; Cecilia, JA.; Solsona, B.... (2020). Enhanced NiO Dispersion on a High Surface Area Pillared Heterostructure Covered by Niobium Leads to Optimal Behaviour in the Oxidative Dehydrogenation of Ethane. Chemistry - A European Journal. 26(42):9371-9381. https://doi.org/10.1002/chem.202000832S937193812642L. Nichols Industry Perspectives: Global petrochemical sector to see robust growth to 2020 Hydrocarbon Processing 2017.Hermabessiere, L., Dehaut, A., Paul-Pont, I., Lacroix, C., Jezequel, R., Soudant, P., & Duflos, G. (2017). Occurrence and effects of plastic additives on marine environments and organisms: A review. Chemosphere, 182, 781-793. doi:10.1016/j.chemosphere.2017.05.096Jia, L., Evans, S., & Linden, S. van der. (2019). Motivating actions to mitigate plastic pollution. 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Applied Catalysis A: General, 550, 151-159. doi:10.1016/j.apcata.2017.11.005Zhang, Z., Zhao, G., Chai, R., Zhu, J., Liu, Y., & Lu, Y. (2018). Low-temperature, highly selective, highly stable Nb2O5–NiO/Ni-foam catalyst for the oxidative dehydrogenation of ethane. Catalysis Science & Technology, 8(17), 4383-4389. doi:10.1039/c8cy01041bSkoufa, Z., Heracleous, E., & Lemonidou, A. A. (2015). On ethane ODH mechanism and nature of active sites over NiO-based catalysts via isotopic labeling and methanol sorption studies. Journal of Catalysis, 322, 118-129. doi:10.1016/j.jcat.2014.11.014Solsona, B., Concepción, P., López Nieto, J. M., Dejoz, A., Cecilia, J. A., Agouram, S., … Rodríguez Castellón, E. (2016). Nickel oxide supported on porous clay heterostructures as selective catalysts for the oxidative dehydrogenation of ethane. Catalysis Science & Technology, 6(10), 3419-3429. doi:10.1039/c5cy01811kPopescu, I., Heracleous, E., Skoufa, Z., Lemonidou, A., & Marcu, I.-C. (2014). Study by electrical conductivity measurements of semiconductive and redox properties of M-doped NiO (M = Li, Mg, Al, Ga, Ti, Nb) catalysts for the oxidative dehydrogenation of ethane. Physical Chemistry Chemical Physics, 16(10), 4962. doi:10.1039/c3cp54817aPopescu, I., Skoufa, Z., Heracleous, E., Lemonidou, A., & Marcu, I.-C. (2015). A study by electrical conductivity measurements of the semiconductive and redox properties of Nb-doped NiO catalysts in correlation with the oxidative dehydrogenation of ethane. Physical Chemistry Chemical Physics, 17(12), 8138-8147. doi:10.1039/c5cp00392jLópez Nieto, J. M., Solsona, B., Grasselli, R. K., & Concepción, P. (2014). Promoted NiO Catalysts for the Oxidative Dehydrogenation of Ethane. Topics in Catalysis, 57(14-16), 1248-1255. doi:10.1007/s11244-014-0288-2Delgado, D., Solsona, B., Ykrelef, A., Rodríguez-Gómez, A., Caballero, A., Rodríguez-Aguado, E., … López Nieto, J. M. (2017). Redox and Catalytic Properties of Promoted NiO Catalysts for the Oxidative Dehydrogenation of Ethane. The Journal of Physical Chemistry C, 121(45), 25132-25142. doi:10.1021/acs.jpcc.7b07066Delgado, D., Sanchís, R., Cecilia, J. A., Rodríguez-Castellón, E., Caballero, A., Solsona, B., & Nieto, J. M. L. (2019). Support effects on NiO-based catalysts for the oxidative dehydrogenation (ODH) of ethane. Catalysis Today, 333, 10-16. doi:10.1016/j.cattod.2018.07.010Ko, E. I., & Weissman, J. G. (1990). Structures of niobium pentoxide and their implications on chemical behavior. Catalysis Today, 8(1), 27-36. doi:10.1016/0920-5861(90)87005-nTauc, J. (1968). Optical properties and electronic structure of amorphous Ge and Si. Materials Research Bulletin, 3(1), 37-46. doi:10.1016/0025-5408(68)90023-8Viezbicke, B. D., Patel, S., Davis, B. E., & Birnie, D. P. (2015). 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Ferric sludge derived from the process of water purification as an efficient catalyst and/or support for the removal of volatile organic compounds

[EN] Ferric chloride solutions are used as coagulants or flocculants in water treatment operations for human consumption. This treatment produces large amounts of clay-type solids formed mainly of montmorillonite with iron oxides and humic substances. This ferric sludge can be used as an efficient catalyst for the removal of volatile organic compounds (VOCs) by total oxidation. This waste isolated in the purification process has been activated by calcinations in air, characterized by several physicochemical techniques and employed as a catalyst for the removal by total oxidation of representative VOCs: toluene, propane and mixtures of toluene/propane with or without water. This ferric sludge has shown a catalytic activity one order of magnitude higher than that of a commercial iron oxide. This high activity has been related to the composition of the sludge (as it contains active metal oxides such as oxides of iron and manganese) and to the porous structure (leading to a reasonably high surface area). Moreover, it can be also used as a support for platinum, showing comparable (or even higher) catalytic activity than a similar platinum catalyst supported on conventional gamma-alumina.The authors would like to acknowledge the DGICYT in Spain CTQ2012-37925-C03-2, CTQ2015-68951-C3-1-R and CTQ2015-68951-C3-3-R. Authors from UV thank the University of Valencia (UV-INV-AE16-484416 project) and MINECO (MAT2017-84118-C2-1-R project) for funding. Finally, authors thank the Electron Microscopy Service of SCSIE of Universitat de Valencia for their support.Sanchis, R.; Dejoz, A.; Vázquez, I.; Vilarrasa-García, E.; Jiménez-Jiménez, J.; Rodríguez-Castellón, E.; López Nieto, JM.... (2019). Ferric sludge derived from the process of water purification as an efficient catalyst and/or support for the removal of volatile organic compounds. Chemosphere. 219:286-295. https://doi.org/10.1016/j.chemosphere.2018.12.002S28629521

Assessing the Electrochemical Performance of Different Nanostructured CeO2 Samples as Anodes for Lithium-Ion Batteries

In this work, six samples of CeO2 are successfully prepared by diverse synthesis routes leading to different microstructures regarding both morphology and particle size. The structural and microstructural characteristics presented by the samples and their influence on the electrochemical response of the prepared anodes are analyzed. In particular, the Ce-CMK3 sample, synthesized from a mesoporous carbon obtained through a CMK3 silica template, displays an enhanced electrochemical response. Thus, capacity values of ~220 mA h g−1 are obtained at a current rate of 0.155 A g−1 after 50 cycles and an excellent cyclability at intermediate current densities. On the other hand, it is observed that the capacity values are satisfactorily recovered at 0.31 A g−1, displaying ~100 mA h g−1 after 550 cycles and efficiencies close to 100%. The electrochemical performance is interpreted considering the microstructural peculiarities of this anode, which are deeply analyzed.Depto. de Química InorgánicaFac. de Ciencias QuímicasTRUEMINECOpu

Tungsten-titanium mixed oxide bronzes: Synthesis, characterization and catalytic behavior in methanol transformation

[EN] Tungsten oxide bronze-based materials show extremely adaptive structural and compositional features that make them suitable for functional properties modulation. Herein we report the preparation of a series of Ti-containing tungsten oxide catalysts presenting a hexagonal tungsten bronze-type structure. The insertion of Ti4+ within the structure (likely in the octahedral framework of the hexagonal tungsten bronze) leads to an increase in the number of strong acid sites, and the disappearance of W5+ surface species found in the undoped tungsten oxide. With the aim of studying the acid-redox properties of the titled catalysts, the catalytic transformation of methanol has been carried out in the presence and the absence of O-2 in the feed. Both catalytic activity and the acid-redox properties of these catalysts are highly dependent on catalyst composition and reaction conditions applied (i.e. in the presence or in the absence O-2 in the feed). Aerobic experiments show the depletion of the redox functionality (i.e. no formaldehyde detected in the products) when Ti4+ is incorporated in the framework (i.e. 100% selectivity to dimethyl ether). On the other hand, all the catalysts show the loss of the redox function and a decrease in the catalytic activity when anaerobic conditions are used. In the absence of oxygen, the catalysts are still active in the dehydration of methanol to dimethyl ether, i.e. they maintain their acid functionality even when oxygen is not present in the feed. The results are discussed in terms of the available surface active sites present in each case.Authors would like to thank DGICYT in Spain for RTI2018-099668-B-C21, CTQ2015-68951-C3-1-R and MAT2017-84118-C2-1-R projects. Authors from ITQ also thank Project SEV-2016-0683 for supporting this research. D.D. thanks MINECO and Severo Ochoa Excellence Program for his fellowship (SVP-2014-068669). Finally, authors thank the Electron Microscopy Service of SCSIE of Universitat de Valencia for their support.Delgado-Muñoz, D.; Soriano Rodríguez, MD.; Solsona Espriu, BE.; Zamora Blanco, S.; Agouram, S.; Concepción Heydorn, P.; López Nieto, JM. (2019). Tungsten-titanium mixed oxide bronzes: Synthesis, characterization and catalytic behavior in methanol transformation. Applied Catalysis A General. 582:1-10. https://doi.org/10.1016/j.apcata.2019.05.026S11058

The prevalence of surface oxygen vacancies over the mobility of bulk oxygen in nanostructured ceria for the total toluene oxidation

AbstractThis paper reveals the key importance of surface oxygen defects in the oxidation catalytic activity of nanostructured ceria. A series of nanostructured rods and cubes with different physico–chemical properties have been synthesized, characterized and tested in the total toluene oxidation. The variation of the temperature and base concentration during the hydrothermal syntheses of nanostructured ceria leads not only to different ceria morphologies with high shape purity, but also to structures with tuneable surface areas and defect concentrations. Ceria nanorods present a higher surface area and a higher concentration of bulk and surface defects than nanocubes associated with their exposed crystal planes, leading to high oxidation activities. However, for a given morphology, the catalytic activity for toluene oxidation is directly related to the concentration of surface oxygen defects and not the overall concentration of oxygen vacancies as previously believed

The key role of nanocasting in gold-based Fe2 O3 nanocasted catalysts for oxygen activation at the metal-support interface

The total oxidation of propane, a representative Volatile Organic Compound, has been studied using gold-based α-Fe2O3 catalysts. Catalysts consisting of gold nanoparticles confined in nanostructured Fe2O3 prepared by a nanocasting route present the highest catalytic activity for propane total oxidation, and the activity is significantly greater than those of gold-based catalysts where iron oxide supports are prepared by other conventional methods, such as calcination. Detailed characterization and Density-functional theory (DFT) studies have been undertaken in order to explain the enhancement in catalytic properties. The presence of confined gold nanoparticles on the nanocast Fe2O3 facilitates the production of highly reactive oxygen vacancies at the metal-support interface, increasing the catalyst performance. Both the development of a microporous/mesoporous structure in the iron oxide support and the presence of a mixed surface phase of Si and Fe oxides, seem to be key parameters, being both features inherent in the nanocasting process from silica templates. Additionally, the catalytic activity is enhanced due to other positive effects, which are closely related to the nanocasting preparation method: i) a higher contact surface area between partially confined small gold nanoparticles in the internal mesoporosity of the nanostructured support and the metal oxide and; ii) a more reducible support due to the presence of more active surface lattice oxygen

Understanding the role of Ti-rich domains in the stabilization of gold nanoparticles on mesoporous silica-based catalysts

The preparation and stabilization of gold nanoparticles with a precise control of size and dispersion is highly attractive for a variety of applications, and a key aspect is thermal stability of the nanoparticles. This paper focuses on understanding the effect of TiO2-based nanodomains, dispersed on mesoporous silicas, and how they control gold nanoparticle stability. The anatase domains have been incorporated through two different strategies: co-hydrolysis of Si and Ti reagents that directly form the mesoporous material through self-assembling with surfactant micelles, or the post-impregnation of the mesosporous silica with Ti(acac)2. Both strategies lead to different incorporation of the anatase domains: partially embedded inside the silica walls, or occupying the mesopores. We have observed that the inclusion in the pores favors the stability of the final material due to a more favorable gold-support interaction and also due to a stabilizing effect associated with a scaffold effect of the anatase crystals, which hinders the collapse of the mesostructure

Zr supported on non-acidic sepiolite for the efficient one-pot transformation of furfural into γ-valerolactone

10 figures y 4 tables.-- Supplementary information available.The growing demand of energy needs the search for alternative energy sources different to fossil fuels. The use of biomass as energy source is one of the most studied, because there are high value products that can be produced from biomass. One of these products is γ-valerolactone, that can be obtained from furfural, which is a biomass derived product. To transform furfural into γ-valerolactone is necessary a bifunctional catalyst and a hydrogen source. In this work, γ-valerolactone was obtained from furfural using 2-propanol as solvent and as hydrogen donor on Zr supported on sepiolite catalysts. It was demonstrated that sepiolite, which is a cheap material, can be used to develop efficient catalysts to produce high yields to γ-valerolactone from furfural in one-pot. The catalysts that presented the highest yield to γ-valerolactone were the ones with intermediate Zr-content (9–17 wt% ZrO2). The highest TOFs have been obtained by those catalysts with Zr-loading up to 9 wt% ZrO2, in which the ZrO2 nanoparticles are well dispersed on the support and no formation of large clusters of ZrO2 has been observed. Lewis and Brønsted acid sites are essential in the catalysts to produce the reactions to transform furfural into γ-valerolactone in one-pot, although in the present work, low concentration of Brønsted acid sites were observed in the catalysts. A possible positive role of basic sites to promote some intermediate steps has been also proposed. The catalytic results obtained are in the order of catalysts with Zr supported on zeolitic supports.A.G. thanks MINECO for the pre-doctoral grant (PRE2018-085211). This work was funded by the MAT2017-84118-C2-1-R, MAT2017-84118-C2-2-R, MCIN/AEI/10.13039/501100011033/projects and FEDER Una manera de hacer Europa. Authors thank the electron microscopy CAI center of UCM. Authors also thank the Generalitat Valenciana for CIAICO/2021/094.Peer reviewe