Electrical conductivity of a MoVTeNbO catalyst in propene oxidation measured in operando conditions

[EN] A complex ac electrical conductivity study was performed on a Te(0.33)MO(3.33) (M = Mo + V + Nb) pure phase (M2-type phase) in operando conditions, using the differential step technique (DST). The aim is to obtain new information about the influence of the oxidation and moisture on the catalytic behaviour of this phase in propene oxidation to acrylic acid. Three successive series of experiments were performed on the same batch of sample: (i) cycles of heating (up to 300, 350 and 400 degrees C, respectively)-cooling (to room temperature) in inert and in the catalytic test mixture, without intermediate oxidation; (ii) the same, but intercalating heating-cooling oxidation cycles (up to 300, 350 and 400 degrees C, respectively) before the corresponding catalytic test runs; and (iii) catalytic testing runs performed by heating up to 400 degrees C in the presence of pre-absorbed or co-adsorbed humidity. Based on the electrical conductivity results, it appears that 350 degrees C is a critical temperature in terms of surface reduction/re-oxidation: below this temperature no major surface changes of the relative oxidation level occur on flushing in dry helium or in the catalytic test mixture, while above it, an important reduction occurs in the same atmospheres. Re-oxidation in oxygen is not efficient if performed below 350 degrees C, but if done above (up to 400 degrees C) the surface recovers almost the initial behaviour. These results suggest the reversibility of the oxidation state of the catalyst surface, which is important in the practical use of this material. The activity and selectivity of acrylic acid formation are discussed in relation with the relative levels of oxidation/reduction of the surface. (C) 2010 Elsevier B.V. All rights reserved.T.B. and J.M.L.N thank for the financial support from DGICYT in Spain through Project CTQ2006-09358/BQU).Caldararu, M.; Scurtu, M.; Hornoiu, C.; Munteanu, C.; Blasco Lanzuela, T.; López Nieto, JM. (2010). Electrical conductivity of a MoVTeNbO catalyst in propene oxidation measured in operando conditions. Catalysis Today. 155(3-4):311-318. doi:10.1016/j.cattod.2010.01.045S3113181553-

Influence of the reactant gas on the electrical properties of alumina-supported tin dioxide catalysts

ENERGIE+GPONon

Possible dual-charge-carrier mechanism of surface conduction on gamma-alumina

We cast a dual-charge-carrier model of surface conductance on gamma-alumina in mathematical form. We then carry out first-principles calculations for various possible atomic-scale structures of the low- and high-temperature charge-carrier interactions with the gamma-alumina surface to estimate the values of the energy parameters in the dual-charge-carrier model. By comparing the values of these energy parameters as determined by first-principles calculations to those obtained by fitting the mathematical form of the dual-charge-carrier model to experimental data, new insight is gained into the nature of the charge-carrier species. The results support the hypothesis that the intrinsic hydrogen content and surface moisture of gamma-alumina provide a possible explanation of the observed thermal dependence of surface conductance

Study of Pt/Sn-Al catalyst for environmental applications

internationa

CO sensing properties of SnO2-CeO2 mixed oxides

SSCI-VIDE+ATARI+GPOInternational audienc

In situ electrical conductivity study of Pt-impregnated VOx/gamma-Al2O3 catalysts in propene deep oxidation

A series of Pt-VOx/gamma-Al2O3 catalysts with vanadium loading corresponding to 5 and 20 wt% V2O5 was prepared by impregnation method. The catalytic performance of the obtained materials was investigated in propene deep oxidation reaction. The catalysts were characterized by N-2 physisorption, chemical analysis, X-ray diffraction (XRD), temperature-programmed reduction (TPR), electron paramagnetic resonance (EPR) spectroscopy, and UV-Vis diffuse reflectance spectroscopy. Alternating current (AC) electrical conductivity measurements (differential steps technique) were performed in situ during propene oxidation, using an own design reactivity cell. The variation in the measured electrical conductance brings information about the relative oxidation state of the catalyst's surface during reaction. It was found by TPR, EPR, and UV-Vis that the presence of platinum facilitates the reduction of V5+ to V4+ species. The catalytic performance of the investigated catalysts was discussed in relation to their structure, reducibility, and conductance