III International Conference

PP-III-98The comparison of TPR runs proved that reducibility of supported nickel oxide speciesmight be modified by TiO 2 introduction method. The reduction courses of catalysts supportedon SiO 2 -TiO 2 containing 10 wt.% of TiO 2 show that nickel is considerably more weakly boundwith the surface of support prepared by one step hydrolysis of chelated titanium isopropoxide(TiPOT) and tetraethoxysilane (TEOS). Catalyst obtained by this method is completelyreduced in the temperature range 290-580 °C (T max ., 420 °C). The TPR result of catalystprepared by deposition of TiO 2 on the silica surface via hydrolysis of TiCl 4 (Method D)demonstrated that reduction occurs in two, party overlapping stages. The obtained profile showsmaxims at temperature 415 °C and 550 °C. On the TPR profile of catalyst prepared bydeposition of TiO 2 on the silica surface via hydrolysis of TiPOT (Method A) one can observemaximum hydrogen uptake at 470 °C. The results show that increase of TiO 2 content in thesupports obtained by deposition of TiO 2 on silica surface leads to Tmax shift towards highertemperature. In the case of one step hydrolysis method reduction of oxide nickel speciessupported on SiO 2 -TiO 2 containing 50 wt.% of TiO 2 occurs in lower temperature range than onSiO 2 -TiO 2 containing 25 wt.% of TiO 2 . After the first TPR run (TPR up to 900 °C), thecatalysts were subjected to re-oxidation at temperature 400 °C followed by the second TPR run(TPR up to 900 °C). The obtained profiles show maxims in the temperature range 300 – 350 °C.Reducibility of the catalysts was related to the TiO 2 phase composition: anatase > rutile >amorphous TiO 2 . SEM results show an affinity of nickel to titania rather than to silica (Fig. 1).Si content, %353025201510530252015105Ti content, %002 3 4 5 6 7 8 9Ni content, %Fig. 1. Correlation between TiO 2 content and Ni content.References1. B.H. Cooper, B..B.l. Donnis, Appl. Catal., A: General, 137 (1996) 20032. R.G. Tailleur, J. Ravigli, S. Quenza, N. Nalencia, Appl. Catal., 282 (2005), 2273. R.B.Watson, U.S. Ozkan, J. Catal., 191 (2000) 124. V. Santes et al., Appl. Catal, A: General, 281 (2005) 121651