III International Conference

PP-II-49synthesis methods such as sol-gel (SG), Pechini (Pch) and mild mechanochemical activation(MA) followed by sintering. The synthesized samples have been characterized by XRD, IRand 29 Si NMR spectroscopy, TG/TGA.According to the thermal analysis of gels synthesized by Ph method, organic precursorsare exothermally decomposed at 200-600 ºC to give carbonates as shown by XRD and IR.The formation of the apatite structure accompanied by a broad exothermal effect starts above830 ºC. In fact, after sintering at 900 ºC during 2 h, the samples synthesized by both the Pchand SG methods are mainly composed of an apatite-type lanthanum silicate. For the systemsprepared by Pch method, the effect of the heating rate and MA of the precursors on apatitephase formation was revealed. The samples obtained via MA followed by annealing for 6-8 hat 1200 ºC contain pure lanthanum silicate of the apatite type.For Ba and Mg-doped lanthanum silicates synthesized by MA method, the conductivitywas measured in the temperature range from 300 to 750 ºC. The electrical measurements forsamples with a residual porosity reveal a low activation energy and rather high ionicconductivity (6.9·10 -4 -1.1·10 -4 S/cm at 500 ºC) of the systems in agreement with the literature[4]. The data of oxygen isotopic exchange revealed that these systems possess a high latticeoxygen ion mobility as well as a high rate of heteroexchange.Ni/lanthanum silicate based cermets prepared via impregnation, modified Pch and ballmixing methods were tested in methane steam reforming (SR). Catalytic activity wasmeasured using a flow reactor at 600-800 ºC. The flow rate of the 7%CH 4 -7%H 2 O in Hereaction mixture was 10 l/h, contact time was 0.77 s. The SR activity of the sample obtainedby the impregnation was shown to be poor due to severe coking. Cermets synthesized bymodified Pch method and ones doped with the complex oxides of perovskite structure insure asufficiently high activity in SR. Moreover, promoted systems have a higher stability to cokingas compared with unpromoted samples. A higher activity and stability of cermets could beprovided by a high Ni dispersion (helps to hinder the carbon formation) and the presence ofoxide promoters with a high lattice oxygen mobility which promote elimination of thedeposited surface carbon.This research is in part supported by European Commission Framework 6 Program(MATSILC Program).References1. O. Yamamoto // Electrochim. Acta 45 (2000) 2423–24352. A.K. Demin, F.Y. Gulbis // Solid State Ion. 135 (2000) 451–4563. H. Yoshioka // J. Alloys and Comp. 408–412 (2006) 649–6524. A. Najib, J. E. H. Sansom, J. R. Tolchard, etc. // DaltonTrans. (2004) 3106–3109253