OP-II-3

PP-III-16H 2consumpition (a.u)(a)391°C550°CH 2consumption (a.u)(b)499°C651°C200 300 400 500Temp (°C)Scanning electron microscopy (SEM) and by the Fourier Transform Infraredspectroscopy (FT-IR). TPR results (Fig. 1) suggest that the addition of Mo shiftedsignificantly the reduction temperature of Fe 3+ to magnetite from 391°C to 499°C andthe further reduction temperature peak from 550°C to 650°C. This observationindicates that Mo hinder the formation of metallic iron increasing the active phasestability. The assignment of the reduction peaks to the individual mechanistic step isnot straightforward in a mixed oxide like Fe 2 O 3 -Ce 0.5 Zr 0.5 O 2 as reduction of Fe 2 O 3 aswell Ce 0.5 Zr 0.5 O 2 by hydrogen is a two step process with considerable overlapping [3].Activity measurements were carried out at atmospheric pressure in a quartz tubemicroreactor at temperatures between 600°C and 750 °C. The iron oxides werereduced by H 2 and oxidized by steam with helium as carrier gas. It was found that Moimproves the stability of 80Fe 2 O 3 -20Ce 0.5 Zr 0.5 O 2 [Fig.2]. A samplemodified with 5 % Mo when testedfor 100 redox cycles, maintain itsactivity nearly unchanged at650°C and retains 90 % of itsactivity at 750°C whereas theamount of produced hydrogenprogressively decreases for theunmodified samples. The resultsindicate that Mo is successful inhindering the sintering.References[1]. Galvita and Sundmacher, Chem. Eng. J., 134 (2007), 168-174.[2]. Galvita et al., Ind. Eng. Chem. Res., 47 (2008), 303-310.[3]. Galvita et al., J. Mater. Sc., 42 (2007), 9300-9307.Normalized amount of produced H 2, n i/n 11,00,90,80,7400 500 600 700750°C650°C650°CTemp (°C)Fig. 1: Experimental H 2 -TPR data for (a) Fe 2 O 3 -Ce 0.5 Zr 0.5 O 2 and(b) Fe 2 O 3 -Ce 0.5 Zr 0.5 O 2 with 2 % Mo promoter.(b)(a)0,60 10 20 30 40 50 60 70 80 90 100Number of redox cyclesFig. 2: Variation of normalized amount of producedH 2 with redox cycles at various temperatures for (a)Fe 2 O 3 -Ce 0.5 Zr 0.5 O 2 , (b) Fe 2 O 3 -Ce 0.5 Zr 0.5 O 2 with 5 %Mo and (c) Fe 2 O 3 -Ce 0.5 Zr 0.5 O 2 with 5 % Mo.(c)469