The use of Pd catalysts on carbon-based structured materials for the catalytic hydrogenation of bromates in different types of water

[EN] The aim of this work is to study the activity of new Pd catalysts, supported on two different nano structured carbon materials, for bromate catalytic hydrogenation. The influence of the support has been studied, obtaining the best results with a palladium catalyst supported on carbon nanofibers (CNF) grown in sintered metal fibers (SMF). The results have shown the importance of the catalyst support in order to minimize the mass-transfer limitations ensuring an efficient catalyst use. In this way the most active catalysts are those with a mesoporous structure containing high dispersed Pd nanoparticles. The activity of this catalyst for bromate reduction has been tested in different types of water, namely, distilled water, natural water and industrial wastewater. It has been shown that the catalyst activity depends on the water matrix and bromate reduction rate depends on the hydrogen partial pressure. The potential use of the catalyst has been studied in a continuous reactor. It has been observed that the catalyst is active without any important deactivation at least during 100 h of reaction, but is necessary to avoid salt precipitation and plugging problems.The authors thank the European Union (European Community's Seventh Framework Programme FP7/2007-2013 under grant agreement no. 226347 Project) for financial support. A.E. Palomares also acknowledges the support from the Spanish Government through the project MAT2012-38567-C02-01.Palomares Gimeno, AE.; Franch Martí, C.; Yuranova, T.; Kiwi-Minsker, L.; Garcia Bordeje, JE.; Derrouiche, S. (2014). The use of Pd catalysts on carbon-based structured materials for the catalytic hydrogenation of bromates in different types of water. Applied Catalysis B: Environmental. 146:186-191. https://doi.org/10.1016/j.apcatb.2013.02.056S18619114

CO Adsorption on Supported Gold Nanoparticle Catalysts: Application of the Temkin Model

The adsorption of CO on the supported gold nanoparticle catalysts Au/TiO2, Au/Fe2O3, and Au/ZrO2 was examined using infrared transmission spectroscopy to quantify the isobaric CO coverage as a function of temperature. The Temkin adsorbate interaction model was then applied to account for the adsorption behavior. To test the general applicability of the Temkin model, this treatment was also applied to three data sets from the literature. This included another real-world catalyst and two model catalysts. All data sets were accurately represented by the Temkin adsorbate interaction model. The resulting thermodynamic metrics are consistent with previous determinations and reflect a particle size-dependence. In particular, the intrinsic adsorption enthalpy at zero CO coverage varies almost linearly with Au particle size, and this trend appears to be correlated with the abundance of low-coordinate Au sites (cf., CN = 6 and 7 for corners and edges, respectively). For very small particles with mostly CN = 6 corner sites, the enthalpy reflects strong binding (cf., −ΔH0 ≈ 78 kJ/mol), while for large particles with mostly CN = 7 edge sites, the enthalpy reflects weaker binding (cf., −ΔH0 ≈ 63 kJ/mol). The results also suggest that these sites are coupled. This study demonstrates that the Temkin adsorbate interaction model accurately represents adsorption data, yields meaningful metrics that are useful for characterizing nanoparticle catalysts, and should be applicable to other adsorption data sets

Impact of potassium on the heats of adsorption of adsorbed CO species on supported Pt particles by using the AEIR method

International audienceThe heats of adsorption at several coverages of the linear and bridged CO species (denoted L and B, respectively) adsorbed on the Pt0 sites of the 2.9 wt% Pt/10% K/Al2O3 catalyst are determined using the Adsorption Equilibrium Infrared spectroscopy method. The addition of K on 2.9% Pt/Al2O3 modifies significantly the adsorption of CO on the Pt particles: (a) the ratio L/B is decreased from 8.4 to 1, (b) a new adsorbed CO species is detected with an IR band at 1763 cm−1, (c) the heats of adsorption of L and B CO species are significantly altered and the positions of their IR bands are shifted. The heats of adsorption of L CO species are decreased: i.e. 206 and 105 kJ/mol at low coverages on Pt/Al2O3 and Pt/K/Al2O3 respectively. Two B CO species denoted B1 and B2, with different heats of adsorption are observed on Pt/K/Al2O3. The heats of adsorption of B2 CO species (major B CO species) are significantly larger than those measured in the absence of K: i.e. 94 and 160 kJ/mol at low coverages on Pt/Al2O3 and Pt/K/Al2O3 respectively, whereas those of B1 CO species (minor species) are similar: 90 kJ/mol at low coverages. These values are consistent with the qualitative High Resolution Electron Energy Loss Spectrometry literature data on Pt(1 1 1) modified by potassium

Heats of adsorption of linear CO species on the Pt sites of a 1.2% Pt-2.7% Sn/Al2O3 catalyst before and after reconstruction and ageing processes

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Heats of Adsorption of Linear and Bridged CO Species Adsorbed on a 3% Ag/Al2O3 Catalyst Using in situ FTIR Spectroscopy under Adsorption Equilibrium

International audienceThe heats of adsorption of linear and bridged CO species adsorbed on Ag0 sites of a reduced 3% Ag/Al2O3 catalyst and of the linear CO species on Ag+ sites of the oxidized catalyst are determined as the function of their respective coverages by using the adsorption equilibrium infrared spectroscopy method previously developed. The evolutions of the intensities of the IR bands of each adsorbed species: 2045 cm-1 and 2000 cm-1 at 300 K, for the linear and bridged CO species, respectively, on Ag0 sites of the reduced solid and 2168 cm-1 for a linear CO species on Ag+ sites of the oxidized solid are determined as a function of the adsorption temperature Ta, at a constant CO adsorption pressure PCO. This provides the evolutions of the coverages of each adsorbed CO species with Ta in isobar conditions that give the individual heats of adsorption of the three adsorbed CO species at several coverages according to an adsorption model. The heats of adsorption of the linear and bridged adsorbed CO species on Ag0 sites vary linearly with their coverages : from E0 = 76 kJ/mol to E1 = 58 kJ/mol for the linear CO species and from E0 = 88 kJ/mol to E1 = 84 kJ/mol for the bridged CO species at coverages 0 and 1, respectively. Volumetric measurements indicate that the total amount of the adsorbed CO species represents a small fraction of the superficial sites of the reduced Ag particles suggesting that they are adsorbed on defect sites. The heat of adsorption of the linear CO species on the Ag+ sites linearly varies with its coverage from E0 = 66 kJ/mol to E1 = 41 kJ/mol at coverages 0 and 1, respectively