Tailoring Gold Nanoparticle Characteristics and the Impact on Aqueous-Phase Oxidation of Glycerol

Poly(vinyl alcohol) (PVA)-stabilized Au nanoparticles (NPs) were synthesized by colloidal methods in which temperature variations (−75 to 75 °C) and mixed H2O/EtOH solvent ratios (0, 50, and 100 vol/vol) were used. The resulting Au NPs were immobilized on TiO2 (P25), and their catalytic performance was investigated for the liquid phase oxidation of glycerol. For each unique solvent system, there was a systematic increase in the average Au particle diameter as the temperature of the colloidal preparation increased. Generation of the Au NPs in H2O at 1 °C resulted in a high observed activity compared with current Au/TiO2 catalysts (turnover frequency = 915 h–1). Interestingly, Au catalysts with similar average particle sizes but prepared under different conditions had contrasting catalytic performance. For the most active catalyst, aberration-corrected high angle annular dark field scanning transmission electron microscopy analysis identified the presence of isolated Au clusters (from 1 to 5 atoms) for the first time using a modified colloidal method, which was supported by experimental and computational CO adsorption studies. It is proposed that the variations in the populations of these species, in combination with other solvent/PVA effects, is responsible for the contrasting catalytic properties

Supported metal nanoparticles with tailored catalytic properties through sol-immobilisation: applications for the hydrogenation of nitrophenols

The use of sol-immobilisation to prepare supported metal nanoparticles is an area of growing importance in heterogeneous catalysis; it affords greater control of nanoparticle properties compared to conventional catalytic routes e.g. impregnation. This work, and other recent studies, demonstrate how the properties of the resultant supported metal nanoparticles can be tailored by adjusting the conditions of colloidal synthesis i.e. temperature and solvent. We further demonstrate the applicability of these methods to the hydrogenation of nitrophenols using a series of tailored Pd/TiO2 catalysts, with low Pd loading of 0.2 wt%. Here, the temperature of colloidal synthesis is directly related to the mean particle diameter and the catalytic activity. Smaller Pd particles (2.2 nm, k = 0.632 min−1, TOF = 560 h−1) perform better than their larger counterparts (2.6 nm, k = 0.350 min−1, TOF = 370 h−1) for the hydrogenation of p-nitrophenol, with the catalyst containing smaller NPs found to have increased stability during recyclability studies, with high activity (>90% conversion after 5 minutes) maintained across 5 catalytic cycles

Extracting structural information of Au colloids at ultra-dilute concentrations: Identification of growth during nanoparticle immobilization

Sol-immobilization is increasingly used to achieve supported metal nanoparticles (NPs) with controllable size and shape; it affords a high degree of control of the metal particle size and yields a narrow particle size distribution. Using state-of-the-art beamlines, we demonstrate how X-ray absorption fine structure (XAFS) techniques are now able to provide accurate structural information on nano-sized colloidal Au solutions at mM concentrations. This study demonstrates: (i) the size of Au colloids can be accurately tuned by adjusting the temperature of reduction, (ii) Au concentration, from 50 mM to 1000 mM, has little influence on the average size of colloidal Au NPs in solution and (iii) the immobilization step is responsible for significant growth in Au particle size, which is further exacerbated at increased Au concentrations. The work presented demonstrates that an increased understanding of the primary steps in sol-immobilization allows improved optimization of materials for catalytic application

Combined spatially resolved operando spectroscopy: New insights into kinetic oscillations of CO oxidation on Pd/γ-Al 2O3

Spatially resolved, combined energy dispersive EXAFS (EDE) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements have been performed over a fixed catalyst bed of Pd/γ-Al 2 O 3 during kinetic oscillations of CO oxidation. The kinetic oscillations of CO oxidation over Pd (or for that matter Pt or Rh) catalysts are a complicated phenomenon that require characterisation techniques with high time resolution and spatial resolution in order to make links between catalyst structure and surface reactivity. By measuring the extent of Pd oxidation at the nanoparticle surface, from Pd K-edge EDE, and matching this with the CO coverage, from DRIFTS spectra, at multiple positions of the fixed bed reactor it is found that the majority of the catalyst undergoes a sharp transition from the CO poisoned catalyst to the highly active, oxidised Pd surface. This transition occurs initially at the end of the catalyst bed, nearest the outlet, and propagates upstream with increasing temperature of the reactor. The oscillations in Pd surface oxide formation and CO coverage are observed only in the first ∼1 mm of the bed, which gives rise to oscillations in CO 2 and O 2 concentrations observed by end-pipe mass spectrometry after the light-off temperature. The catalyst initially exists as less active, CO poisoned metallic Pd nanoparticles before light-off which transition to a highly active state after light-off when the Pd nanoparticle surface becomes dominated by chemisorbed oxygen. Kinetic oscillations only occur at the front of the catalyst bed where there is sufficient concentration of CO in the gas phase to compete with O 2 for adsorption sites at the catalyst surface. We demonstrate the complex nature of the evolving catalyst structure and surface reactivity during catalytic operation and the need for spatially resolved operando methods for understanding and optimising catalyst technologies

National institutional systems’ hybridisation through interdependence. The case of EU-Russia gas relations

International audienceThe interdependencies between the EU and its external natural gas suppliers and Russia question the transformative impact of interdependence linked to hybridization processes. Our approach combines theories of institutional change, and French Regulation Theory. These approaches lead to a new look to characterize the way in which the confrontation of two regulatory systems (EU and Russia) is resolved today. The importance of the European market leads however to an adaptation of the Russian governance model for gas exchanges. But it also implies a transformation of the European model. The competitive norm acts as a lever to bring about hybridization of regulations in the Russian gas sector and EU energy policy

Parents’ Promotion of Psychological Autonomy, Psychological Control, and Mexican–American Adolescents’ Adjustment

Mexican–American adolescents are at an elevated risk for adjustment difficulties. In an effort to identify parenting practices that can affect the adjustment of Mexican–American youth, the current study examined parents’ promotion of psychological autonomy and parents’ psychological control as perceived by Mexican–American early adolescents, and explored their associations with adolescents’ adjustment in the context of acculturation. In 5th grade, 134 (54.5% female) Mexican–American adolescents reported on their acculturation level and the parenting practices of their mothers and fathers. In 5th and 7th grade, adolescents also reported on their depressive symptoms, number of delinquent friends, and self-worth. Perceptions of promotion of psychological autonomy and of psychological control were positively correlated. However, perceptions of more promotion of psychological autonomy and of less psychological control predicted fewer depressive symptoms 2 years later. Perceptions of more promotion of psychological autonomy also predicted fewer delinquent friends two years later. Finally, perceptions of more promotion of psychological autonomy predicted higher self-worth only among less acculturated adolescents. The study underscores the roles that promotion of psychological autonomy and psychological control may play in Mexican–American children’s well-being during early adolescence

Supported Metal Nanoparticles with Tailored Catalytic Properties through Sol immobilisation: Applications for the Hydrogenation of Nitrophenols

Colloidal Pd nanoparticles, prepared at different temperatures and supported on TiO2 support via sol immobilisation were studied for their performance in the catalytic hydrogenation of nitrophenols. The physicochemical properties of the catalysts were characterised in depth using a range of techniques, including UV-vis spectroscopy, TEM, IR and XAFS. The dataset contains TEM micrographs, as well as Origin and Athena (XAFS) files relating to the catalyst characterisation. The catalytic performance data for the aforementioned hydrogenation reaction, including conversion profiles and first order kinetics, is also documented.</span