Thermocatalytic CO2 Conversion over a Nickel-Loaded Ceria Nanostructured Catalyst: A NAP-XPS Study

Despite the increasing economic incentives and environmental advantages associated to their substitution, carbon-rich fossil fuels are expected to remain as the dominant worldwide source of energy through at least the next two decades and perhaps later. Therefore, both the control and reduction of CO2 emissions have become environmental issues of major concern and big challenges for the international scientific community. Among the proposed strategies to achieve these goals, conversion of CO2 by its reduction into high added value products, such as methane or syngas, has been widely agreed to be the most attractive from the environmental and economic points of view. In the present work, thermocatalytic reduction of CO2 with H-2 was studied over a nanostructured ceria-supported nickel catalyst. Ceria nanocubes were employed as support, while the nickel phase was supported by means a surfactant-free controlled chemical precipitation method. The resulting nanocatalyst was characterized in terms of its physicochemical properties, with special attention paid to both surface basicity and reducibility. The nanocatalyst was studied during CO2 reduction by means of Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS). Two different catalytic behaviors were observed depending on the reaction temperature. At low temperature, with both Ce and Ni in an oxidized state, CH4 formation was observed, whereas at high temperature above 500 degrees C, the reverse water gas shift reaction became dominant, with CO and H2O being the main products. NAP-XPS was revealed as a powerful tool to study the behavior of this nanostructured catalyst under reaction conditions

Nanointegracion: obtención controlada de nanoestructuras de óxido de grafeno reducido interconectadas en áreas macroscópicamente extendidas mediante la técnica de Langmuir Blodgett

El objetivo del presente trabajo es obtener películas delgadas de óxido de grafeno (GO) empleando la técnica de Langmuir-Blodgett (L-B) y posteriormente producir la reducción de la película, analizando distintos métodos, para obtener óxido de grafeno reducido (rGO). Con el objetivo de caracterizar als muestras de GO y rGO, las mismas fueron estudiadas por microscopía de fuerza atómica (AFM), micro-Raman y espectroscopía fotoelectrónica de rayos X (XPS) con resolución espacial nanométrica. Se realizaron además medidas de conductividad tanto a escala macro como nanométrica utilizando una estación de prueba y un nanomanipulador acoplado a un equipo de microscopía electrónica de barrido (SEM). Finalmente se correlacionaron el estado químico, la estructura y los defectos presentes en las películas delgadas de rGO con sus propiedades de transporte.El GO fue sintetizado mediante el método de Hummers [1], y se depositó sobre Si(100) empleando la técnica de L-B. El aspecto de los depósitos fue analizado mediante SEM. El espesor de las láminas de GO y rGO se estudió mediante AFM encontrándose para una lámina de rGO un espesor de 1,3±0,1nm, que corresponde al valor esperado para una única lámina de óxido de grafeno. Del análisis de los espectros Raman se puede apreciar una disminución de la banda D asociada a sitios defectuosos de la red [2] mientras que los resultados de XPS realizados in-situ durante un tratamiento térmico en ultra alto vacío permitieron cuantificar la reducción del material e identificar las especies químicas presentes en cada muestra. De acuerdo a las medidas de conductividad, las películas delgadas poseen un comportamiento semiconductor hasta que son reducidas a temperaturas en UHV, alcanzando entonces un carácter óhmico con una elevada conductividad del orden de 105 S/m, la mayor reportada hasta el momento en la literatura [3,4] para compuestos del tipo del rGO.El conjunto de datos experimentales demuestra por una parte la posibilidad de realizar depósitos controlados de GO por L-B y por otro lado, a partir de los resultados de caracterizaciones estructurales y espectroscópicas obtenidos, la eficiencia del proceso de reducción térmico para producir rGO conductor con baja densidad de defectos y una alta relación C/O. Este método de producción tiene gran potencial debido a que abre la posibilidad de sintetizar de forma controlada desde monocapas hasta multicapas de materiales del tipo de los grafenos con propiedades de transporte controladas tanto como aislante o como conductor.Facultad de Ciencias Exacta

Nanointegracion: obtención controlada de nanoestructuras de óxido de grafeno reducido interconectadas en áreas macroscópicamente extendidas mediante la técnica de Langmuir Blodgett

El objetivo del presente trabajo es obtener películas delgadas de óxido de grafeno (GO) empleando la técnica de Langmuir-Blodgett (L-B) y posteriormente producir la reducción de la película, analizando distintos métodos, para obtener óxido de grafeno reducido (rGO). Con el objetivo de caracterizar als muestras de GO y rGO, las mismas fueron estudiadas por microscopía de fuerza atómica (AFM), micro-Raman y espectroscopía fotoelectrónica de rayos X (XPS) con resolución espacial nanométrica. Se realizaron además medidas de conductividad tanto a escala macro como nanométrica utilizando una estación de prueba y un nanomanipulador acoplado a un equipo de microscopía electrónica de barrido (SEM). Finalmente se correlacionaron el estado químico, la estructura y los defectos presentes en las películas delgadas de rGO con sus propiedades de transporte.El GO fue sintetizado mediante el método de Hummers [1], y se depositó sobre Si(100) empleando la técnica de L-B. El aspecto de los depósitos fue analizado mediante SEM. El espesor de las láminas de GO y rGO se estudió mediante AFM encontrándose para una lámina de rGO un espesor de 1,3±0,1nm, que corresponde al valor esperado para una única lámina de óxido de grafeno. Del análisis de los espectros Raman se puede apreciar una disminución de la banda D asociada a sitios defectuosos de la red [2] mientras que los resultados de XPS realizados in-situ durante un tratamiento térmico en ultra alto vacío permitieron cuantificar la reducción del material e identificar las especies químicas presentes en cada muestra. De acuerdo a las medidas de conductividad, las películas delgadas poseen un comportamiento semiconductor hasta que son reducidas a temperaturas en UHV, alcanzando entonces un carácter óhmico con una elevada conductividad del orden de 105 S/m, la mayor reportada hasta el momento en la literatura [3,4] para compuestos del tipo del rGO.El conjunto de datos experimentales demuestra por una parte la posibilidad de realizar depósitos controlados de GO por L-B y por otro lado, a partir de los resultados de caracterizaciones estructurales y espectroscópicas obtenidos, la eficiencia del proceso de reducción térmico para producir rGO conductor con baja densidad de defectos y una alta relación C/O. Este método de producción tiene gran potencial debido a que abre la posibilidad de sintetizar de forma controlada desde monocapas hasta multicapas de materiales del tipo de los grafenos con propiedades de transporte controladas tanto como aislante o como conductor.Facultad de Ciencias Exacta

Inorganically coated colloidal quantum dots in polar solvents using a microemulsion-assisted method

The dielectric nature of organic ligands capping semiconductor colloidal nanocrystals (NCs) makes them incompatible with optoelectronic applications. For this reason, these ligands are regularly substituted through ligand-exchange processes by shorter (even atomic) or inorganic ones. In this work, an alternative path is proposed to obtain inorganically coated NCs. Differently to regular ligand exchange processes, the method reported here produces core-shell NCs and the removal of the original organic shell in a single step. This procedure leads to the formation of connected NCs resembling 1D worm-like networks with improved optical properties and polar solubility, in comparison with the initial CdSe NCs. The nature of the inorganic shell has been elucidated by X-ray Absorption Near Edge Structure (XANES), Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Photoelectron Spectroscopy (XPS). The 1D morphology along with the lack of long insulating organic ligands and the higher solubility in polar media turns these structures very attractive for their further integration into optoelectronic devices

The impact of surgical delay on resectability of colorectal cancer: An international prospective cohort study

AIM: The SARS-CoV-2 pandemic has provided a unique opportunity to explore the impact of surgical delays on cancer resectability. This study aimed to compare resectability for colorectal cancer patients undergoing delayed versus non-delayed surgery. METHODS: This was an international prospective cohort study of consecutive colorectal cancer patients with a decision for curative surgery (January-April 2020). Surgical delay was defined as an operation taking place more than 4 weeks after treatment decision, in a patient who did not receive neoadjuvant therapy. A subgroup analysis explored the effects of delay in elective patients only. The impact of longer delays was explored in a sensitivity analysis. The primary outcome was complete resection, defined as curative resection with an R0 margin. RESULTS: Overall, 5453 patients from 304 hospitals in 47 countries were included, of whom 6.6% (358/5453) did not receive their planned operation. Of the 4304 operated patients without neoadjuvant therapy, 40.5% (1744/4304) were delayed beyond 4 weeks. Delayed patients were more likely to be older, men, more comorbid, have higher body mass index and have rectal cancer and early stage disease. Delayed patients had higher unadjusted rates of complete resection (93.7% vs. 91.9%, P = 0.032) and lower rates of emergency surgery (4.5% vs. 22.5%, P < 0.001). After adjustment, delay was not associated with a lower rate of complete resection (OR 1.18, 95% CI 0.90-1.55, P = 0.224), which was consistent in elective patients only (OR 0.94, 95% CI 0.69-1.27, P = 0.672). Longer delays were not associated with poorer outcomes. CONCLUSION: One in 15 colorectal cancer patients did not receive their planned operation during the first wave of COVID-19. Surgical delay did not appear to compromise resectability, raising the hypothesis that any reduction in long-term survival attributable to delays is likely to be due to micro-metastatic disease

Small Angle Scattering Techniques for the Study of Catalysts and Catalytic Processes

Small-Angle Scattering (SAS) techniques are essential tools for the characterization of catalysts before, during and after catalytic reactions. Either based on X-Rays (SAXS) or neutrons (SANS), they provide unique structural information that helps to understand catalytic processes at the nanoscale level, allowing a rational improvement of the catalysts design. In this review, we present the key aspects involved in the use of these techniques in the catalysis field. Firstly, we introduce some of the fundamentals of the techniques and describe their main features and their impact in the catalyst design. Then, we analyze key examples of the use of SAS to study catalysts’ structure through ex situ analysis, focusing on examples involving different porous materials and metallic nanoparticles. Afterwards, we discuss in situ and operando approaches for studying catalytical processes monitored using SAS. Finally, we present perspectives and challenges for the future use of SAS in the catalysis field

Elucidating the Role of the Metal Catalyst and Oxide Support in the Ru/CeO2-Catalyzed CO2 Methanation Mechanism

This study addresses the yet unresolved CO2 methanation mechanism on a Ru/CeO2 catalyst by means of near-ambient-pressure X-ray photoelectron spectroscopy (NAP–XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) complemented with periodic density functional theory (DFT) calculations. NAP–XPS results show that the switch from H2 to CO2 + H2 mixture oxidizes both the Ru and CeO2 phases at low temperatures, which is explained by the CO2 adsorption modes assessed by means of DFT on each representative surface. CO2 adsorption on Ru is dissociative and moderately endergonic, leading to polybonded Ru-carbonyl groups whose hydrogenation is the rate-determining step in the overall process. Unlike on Ru metal, CO2 can be strongly adsorbed as carbonates on ceria surface oxygen sites or on the reduced ceria at oxygen vacancies as carboxylates (CO2–δ), resulting in the reoxidation of ceria. Carboxylates can then evolve as CO, which is released either via direct splitting at relatively low temperatures or through stable formate species at higher temperatures. DRIFTS confirm the great stability of formates, whose depletion relates with CO2 conversion in the reaction cell, while carbonates remain on the surface up to higher temperatures. CO generation on ceria serves as an additional reservoir of Ru-carbonyls, cooperating to the overall CO2 methanation process. Altogether, this study highlights the noninnocent role of the ceria support in the performance of Ru/CeO2 toward CO2 methanation.The authors thank the financial support of the Spanish Ministry of Economy and Competitiveness (Project CTQ2015-67597-C2-2-R and grant FJCI-2015-23769), the Spanish Ministry of Science and Innovation (PID2019-105960RB-C22), Generalitat Valenciana (Project PROMETEO/2018/076), and the EU (FEDER funding). A.D.-Q. and M.G.-M. acknowledge the financial support from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement no. 713567 and Science Foundation Ireland Research Centre award 12/RC/2278_P2. F.C.H. acknowledges the Argentinian National Research Council (CONICET) for the financial support. C.E. acknowledges funding from the MICINN/FEDER RTI2018-093996-B-32 project. The computational results of this research have been achieved using the DECI resource Salomon based in the Czech Republic at the IT4Innovations National Supercomputing Center with support from the PRACE aisbl. The DJEI/DES/SFI/HEA Irish Centre for High-End Computing (ICHEC) is also acknowledged for the provision of computational facilities

Insights into the Oxygen Vacancy Filling Mechanism in CuO/CeO2 Catalysts: A Key Step Toward High Selectivity in Preferential CO Oxidation

The preferential CO oxidation (CO-PROX) reaction is paramount for the purification of reformate H2-rich streams, where CuO/CeO2 catalysts show promising opportunities. This work sheds light on the lattice oxygen recovery mechanism on CuO/CeO2 catalysts during CO-PROX reaction, which is critical to guarantee both good activity and selectivity, but that is yet to be well understood. Particularly, in situ Raman spectroscopy reveals that oxygen vacancies in the ceria lattice do not form in significant amounts until advanced reaction degrees, whereas pulse O2 isotopic tests confirm the involvement of catalyst oxygen in the CO and H2 oxidation processes occurring at all stages of the CO-PROX reaction (Mars–van Krevelen). Further mechanistic insights are provided by operando near-ambient pressure X-ray photoelectron spectroscopy (NAP–XPS) and near edge X-ray absorption fine structure (NEXAFS) experiments, which prove the gradual CuO reduction and steady oxidized state of Ce ions until the very surface reduction of CeO2 at the point of selectivity loss. Experiments are complemented by density functional theory (DFT) calculations, which reveal a more facile oxygen refill according to the trend CuO > CeO2 > Cu2O. Overall, this work concludes that the oxygen recovery mechanism in CO-PROX switches from a direct mechanism, wherein oxygen restores vacancy sites in the partially reduced CuO particles, to a synergistic mechanism with the participation of ceria once CuxO particles reach a critical reduction state. This mechanistic switch ultimately results in a decrease in CO conversion in favor of the undesired H2 oxidation, which opens-up future research on potential strategies to improve oxygen recovery.The authors thank the financial support of the Spanish Ministry of Economy and Competitiveness (Project CTQ2015-67597-C2-2-R and grant FJCI-2015-23769), the Spanish Ministry of Education, Culture and Sports (grant FPU14/01178), the Generalitat Valenciana (Project PROMETEO/2018/076) and the EU (FEDER funding). F.C.H. acknowledges the Argentinian National Research Council (CONICET) for financial support

Películas de óxidos de grafeno altamente reducido: diseño, síntesis, caracterización y aplicaciones

En este trabajo se presenta la síntesis controlada de películas delgadas de óxido de grafeno (GO) mediante la técnica Langmuir-Blodgett (LB) y su posterior reducción por diferentes vías para obtener películas de óxido de grafeno reducido (rGO). Este método de producción tiene gran potencial debido a que abre la posibilidad de sintetizar de forma controlada desde monocapas hasta multicapas de materiales del tipo de los grafenos, con propiedades de transporte controladas como potencial plataforma para diversas aplicaciones en el área de nanotecnología. En particular se presenta la obtención de un nanocompuesto, incorporando sobre la película de rGO nanohilos de plata (Ag), los cuales ya han mostrado capacidad como biosensores.Facultad de Ciencias Exacta

Películas de óxidos de grafeno altamente reducido: diseño, síntesis, caracterización y aplicaciones

En este trabajo se presenta la síntesis controlada de películas delgadas de óxido de grafeno (GO) mediante la técnica Langmuir-Blodgett (LB) y su posterior reducción por diferentes vías para obtener películas de óxido de grafeno reducido (rGO). Este método de producción tiene gran potencial debido a que abre la posibilidad de sintetizar de forma controlada desde monocapas hasta multicapas de materiales del tipo de los grafenos, con propiedades de transporte controladas como potencial plataforma para diversas aplicaciones en el área de nanotecnología. En particular se presenta la obtención de un nanocompuesto, incorporando sobre la película de rGO nanohilos de plata (Ag), los cuales ya han mostrado capacidad como biosensores.Facultad de Ciencias Exacta