Carbon nanotube-supported Ni–CeO2 catalysts. Effect of the support on the catalytic performance in the low-temperature WGS reaction

The low temperature water-gas shift (WGS) reaction has been studied over two commercial multiwall carbon nanotubes-supported nickel catalysts promoted by ceria. For comparison purposes, activated carbon-supported catalysts have also been studied. The catalytic performance and the characterization by N2 adsorption analysis, powder X-ray diffraction (XRD), temperature-programmed reduction with H2 (TPR-H2), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analysis showed that the surface chemistry has an important effect on the dispersion of ceria. As a result, ceria was successfully dispersed over the carbon nanotubes (CNTs) with less graphitic character, and the catalyst afforded better activity in WGS than the catalyst prepared over massive ceria. Moreover, a 20 wt.% CeO2 loading over this support was more active than the analogous catalyst with a 40 wt.% loading. The ceria nanoparticles were smaller when the support was previously oxidized, however this resulted in a decrease of the activity.

Role of the interfacial water structure on electrocatalysis: Oxygen reduction on Pt(1 1 1) in methanesulfonic acid

Most of electrocatalytic reactions occur in an aqueous environment. Understanding the influence of water structure on reaction dynamics is fundamental in electrocatalysis. In this work, the role of liquid water structure on the oxygen reduction at Pt(1 1 1) electrode is analyzed in methanesulfonic (MTSA) and perchloric acids. This is because these different anions can exert a different influence on liquid water structure. Results reveal a lower ORR electrode activity in MTSA than in HClO4 solutions and they are discussed in light of anion's influence on water structural ordering. From them, the existence of an outer-sphere, rate determining, step in the ORR mechanism is suggested.

CeO2-promoted Ni/activated carbon catalysts for the water–gas shift (WGS) reaction

The low temperature water–gas shift (WGS) reaction has been studied over carbon-supported nickel catalysts promoted by ceria. To this end, cerium oxide has been dispersed (at different loadings: 10, 20, 30 and 40 wt.%) on the activated carbon surface with the aim of obtaining small ceria particles and a highly available surface area. Furthermore, carbon- and ceria-supported nickel catalysts have also been studied as references. A combination of N2 adsorption analysis, powder X-ray diffraction, temperature-programmed reduction with H2, X-ray photoelectron spectroscopy and TEM analysis were used to characterize the Ni–CeO2 interactions and the CeO2 dispersion over the activated carbon support. Catalysts were tested in the low temperature WGS reaction with two different feed gas mixtures: the idealized one (with only CO and H2O) and a slightly harder one (with CO, CO2, H2, and H2O). The obtained results show that there is a clear effect of the ceria loading on the catalytic activity. In both cases, catalysts with 20 and 10 wt.% CeO2 were the most active materials at low temperature. On the other hand, Ni/C shows a lower activity, this assessing the determinant role of ceria in this reaction. Methane, a product of side reactions, was observed in very low amounts, when CO2 and H2 were included in the WGS feed. Nevertheless, our data indicate that the methanation process is mainly due to CO2, and no CO consumption via methanation takes place at the relevant WGS temperatures. Finally, a stability test was carried out, obtaining CO conversions greater than 40% after 150 h of reaction.

Evaluation of the multi-element capabilities of collision/reaction cell inductively coupled plasma - mass spectrometry in wine analysis

This work explores the multi-element capabilities of inductively coupled plasma - mass spectrometry with collision/reaction cell technology (CCT-ICP-MS) for the simultaneous determination of both spectrally interfered and non-interfered nuclides in wine samples using a single set of experimental conditions. The influence of the cell gas type (i.e. He, He+H2 and He+NH3), cell gas flow rate and sample pre-treatment (i.e. water dilution or acid digestion) on the background-equivalent concentration (BEC) of several nuclides covering the mass range from 7 to 238 u has been studied. Results obtained in this work show that, operating the collision/reaction cell with a compromise cell gas flow rate (i.e. 4 mL min−1) improves BEC values for interfered nuclides without a significant effect on the BECs for non-interfered nuclides, with the exception of the light elements Li and Be. Among the different cell gas mixtures tested, the use of He or He+H2 is preferred over He+NH3 because NH3 generates new spectral interferences. No significant influence of the sample pre-treatment methodology (i.e. dilution or digestion) on the multi-element capabilities of CCT-ICP-MS in the context of simultaneous analysis of interfered and non-interfered nuclides was observed. Nonetheless, sample dilution should be kept at minimum to ensure that light nuclides (e.g. Li and Be) could be quantified in wine. Finally, a direct 5-fold aqueous dilution is recommended for the simultaneous trace and ultra-trace determination of spectrally interfered and non-interfered elements in wine by means of CCT-ICP-MS. The use of the CCT is mandatory for interference-free ultra-trace determination of Ti and Cr. Only Be could not be determined when using the CCT due to a deteriorated limit of detection when compared to conventional ICP-MS.