Effect of the Reduction Temperature of PdAg Nanoparticles during the Polyol Process in the Ethanol Electrooxidation Reaction

This work reports the effect of reduction temperature during the synthesis of PdAg catalysts through the polyol process and their evaluation in the ethanol electrooxidation reaction (EOR). The characterization was performed using Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD). The electrochemical evaluation for the ethanol electrooxidation reaction was implemented in alkaline medium using chronoamperometry (CA) and cyclic voltammetry (CV). An important effect of the reduction temperature on electroactivity and catalytic stability was observed: both the maximum current density and the catalytic stability were higher in the catalyst synthesized at the highest temperature (135°C). This performance was associated with the extent of the interaction between Pd and Ag which was measured in terms of the structural expansion of Pd

Variable speed liquid chiller drop-in modeling for predicting energy performance of R1234yf as low-GWP refrigerant

This paper presents a model for a variable-speed liquid chiller integrating a compressor model based on Buckingham π-theorem to accurately predict the system performance when R134a is replaced with R1234yf, using a wide range of data obtained from an experimental setup. Relevant variables such as temperature, pressure, mass and volumetric flow rates, compressor power consumption and rotation speed were measured at several positions along the refrigeration and secondary circuits and were used to validate the developed model. Model results show that cooling capacity and power consumption predicted values are in good agreement with experimental data, within ±5%, being slightly higher for the deviation obtained for R134a than for R1234yf. Moreover, model results indicate that R1234yf has a reduction of coefficient of performance (COP) compared with R134a (between 2 and 11.3%), and that R1234yf COP reduction is diminished at intermediate volumetric flow rate and higher inlet temperature for the evaporator secondary fluid, respectively. On the other hand, an environmental analysis based on TEWI (total equivalent warming impact) method showed that direct emissions are almost negligible for R1234yf. However, there are no environmental benefits in terms of indirect greenhouse gas emissions using R1234yf without system modifications (as for instance the addition of internal heat exchanger or R1234yf new design components), which are required to reduce the liquid chiller climate change contribution using it as low GWP alternative in comparison with the typically used R134a refrigerant

Fast route to obtain Al2O3-based nanocomposites employing graphene oxide: Synthesis and Sintering

A fast approach based on microwave technology was employed for the sintering of novel composites of alumina and using graphene oxide (GO) as susceptor. The thermal stability and structure of GO materials produced by chemical oxidation of graphite were characterized. The morphology, structure and mechanical properties of the composites sintered by microwave approach were reported to the counterparts sintered by conventional method. The results indicated the formation of an interconnecting graphene network promoted the electrical conductivity in the composite having only 2 wt.% GO. Hardness and elastic modulus decreased significantly in samples sintered by conventional method due to lower values of density while microwave technology allowed to achieve a positive effect on the densification and showed a smaller grain size when compared to the one achieved by conventional heating. (C) 2014 Elsevier Ltd. All rights reserved.Financial support from European Commission (project no. NMP3-SL-2010-246073), Universidad Politecnica de Valencia (project SP20120677) and Ministerio de Economia y Competitividad - MINECO (project TEC2012-37532-C02-01, co-funded by ERDF (European Regional Development Funds) is gratefully acknowledged. A.B. acknowledges the Spanish Ministry of Science and Innovation (contract JCI-2011-10498). A.P. acknowledges support from Romanian Authority for Scientific Research - UEFISCDI (project no. PN-II-RU-PD-2012-3-0124).Benavente Martínez, R.; Pruna, AI.; Borrell Tomás, MA.; Salvador Moya, MD.; Pullini, D.; Penaranda-Foix, FL.; Busquets Mataix, DJ. (2015). Fast route to obtain Al2O3-based nanocomposites employing graphene oxide: Synthesis and Sintering. Materials Research Bulletin. 64:245-251. https://doi.org/10.1016/j.materresbull.2014.12.075S2452516

Full factorial design applied to the synthesis of Pd-?Ag nanobars by the polyol method and the perspective for ethanol oxidation

Full factorial design methodology was applied to the synthesis and optimization of Pd–Ag nanobars usingthe polyol process as the reducer. The concentration of Br? ions, the temperature and the reaction timewere selected as factors to study, whereas the yield (% nanobars) was the response to be analyzed. Thenanoparticles were characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy,transmission electron microscopy, high-resolution transmission electron microscopy and X-rayphotoelectron spectroscopy. The nanoparticles were also tested for the ethanol electro-oxidationreaction by cyclic voltammetry in alkaline solution. The three factors had a positive effect onthe response: the nanobar yield increased as the level of the variables changed from ?1 to +1. Thetemperature and reaction time were the most determinant variables (main and interacting) on thenanobar yield, whereas the concentration of Br? influenced the yield to a lesser extent. After designingthree optimum experiments, a maximum nanobar yield of 47.3% was obtained. The more negativeelectro-oxidation onset, higher current density and more negative current peak potential show that theincorporation of Ag into Pd nanobars improves the kinetic and thermodynamic behavior towards theethanol electro-oxidation reaction compared with that obtained with nanometrically pure Pd nanobars.This improvement is the result of surface modification caused by the incorporation of Ag in theformation of Pd–Ag bimetallic nanobars with (200) surfaces