Ni based mixed oxide materials for CH4 oxidation under redox cycle conditions

✍ Scribed by Raffaella Villa; Cinzia Cristiani; Gianpiero Groppi; Luca Lietti; Pio Forzatti; Ugo Cornaro; Stefano Rossini

• Publisher: Elsevier Science
• Year: 2003
• Tongue: English
• Weight: 154 KB
• Volume: 204-205
• Category: Article
• ISSN: 1381-1169
• DOI: 10.1016/s1381-1169(03)00346-7

✦ Synopsis

The preparation, characterization and redox properties of Ni-Al-O and Ni-Mg-Al-O mixed oxides for CH 4 chemical looping combustion (CLC) is addressed in this study. Ni-Al-O samples having different Ni/Al ratios (0.5-2.25), prepared by coprecipitation, consist after calcination at 1000 • C of cubic NiO and NiAl 2 O 4 spinel. A similar phase composition is obtained for Ni-Mg-Al-O, with Mg partitioned in the two phases. The presence of NiAl 2 O 4 prevents the crystal size growth of NiO with respect to pure NiO; further limit of the sintering of the cubic oxide was observed in presence of Mg. Reduction of the samples by H 2 occurs in two steps, associated with reduction of Ni 2+ in NiO and NiAl 2 O 4 . Mg stabilizes Ni 2+ in both the cubic oxide and the spinel phase and improves regenerability upon repeated redox cycles. Temperature programmed reduction with CH 4 (CH 4 -TPR) experiments showed poor selectivity to CO 2 and H 2 O, being CO and H 2 the most abundant products. Also, formation of coke is observed over the samples. The same behavior is observed in CH 4 /O 2 pulse experiments; however, in the case of the Mg-containing system, coke formation can be avoided by co-feeding H 2 O along with CH 4 .