Catalysis Letters Vol. 74, No. 1–2, 2001 31 Highly stable Ni catalyst supported on Ce–ZrO 2 for oxy-steam reforming of methane Hyun-Seog Roh a , Ki-Won Jun a , Wen-Sheng Dong a , Sang-Eon Park a,∗ and Young-Soon Baek b a Catalysis Center for Molecular Engineering, Korea Research Institute of Chemical Technology, PO Box 107, Yusong, Taejon 305-600, Korea b LNG Technology Research Center, Korea Gas Corporation, 973 Dongchun-Dong, Yeonsu-Ku, Incheon 406-130, Korea Received 30 November 2000; accepted 4 April 2001 A novel catalyst, Ni/Ce–ZrO 2 , exhibits very high catalytic activity and stability even in the stoichiometric steam reforming of methane (H 2 O/CH 4 = 1). Furthermore, when it was employed in oxy-steam reforming, it gave enhanced CH 4 conversion (99.1%) at 750 ◦ C and the activity was maintained for 100 h. The high catalyst stability is mainly ascribed to the synergistic effect of the Ce modifier resulting from high capacity to store oxygen and high ability to produce mobile oxygen. KEY WORDS: Ni/Ce–ZrO 2 ; methane; steam reforming; oxy-steam reforming; Ce modifier 1. Introduction Production of hydrogen has received much attention in recent years, due to the importance of hydrogen as a clean source of energy as well as the increased demand in chemi- cal industry [1–3]. Steam reforming of methane (SRM) is a widely practiced technology for hydrogen production. The reaction is highly endothermic. Although stoichiometry for the SRM suggests that only one mole of water is required for one mole of methane (CH 4 + H 2 O → CO + 3H 2 ), usu- ally excess steam is used to reduce carbon formation. Be- cause of the excess steam, the cost of operating an SRM plant increases. Furthermore, the H 2 /CO ratio is over 3 in SRM, which does not fit for methanol synthesis or Fischer– Tropsch synthesis. As an alternative, partial oxidation of methane (POM) has advantages such as mild exothermicity, high conversion, high selectivity, suitable H 2 /CO ratio and very short residence time [3]. However, POM has also dis- advantages such as explosion danger and carbon formation. Due to these demerits, catalytic POM has not been commer- cialized even though it is estimated to be more economical than SRM [1]. As another alternative, oxy-steam reforming (combination of POM and SRM) could be considered. By co-feeding steam and oxygen, one can avoid explosion dan- ger in POM and lessen additional steam cost in SRM, and the H 2 /CO ratio can be controlled by changing the feeding rate of steam or oxygen per methane. Furthermore, one can expect enhanced CH 4 conversion and H 2 yield by combina- tion of these two reforming reactions. Besides these advan- tages, increasing the portion of exothermic POM reaction could reduce required energy for the reforming reaction. In 1991, Green and co-workers [4] reported that 1% Ir/Al 2 O 3 showed high activities with different compositions of CH 4 , O 2 , and CO 2 . In 1994, Choudhary et al. [5] reported syn- ∗ To whom correspondence should be addressed. gas formation by coupled exothermic oxidative conversion and endothermic CO 2 and steam reforming of methane over NiO/CaO catalyst. They suggested that the coupled process can be made mildly exothermic, nearly thermoneutral, or mildly endothermic by manipulating the process conditions. Recently, zirconia as a support was applied to Ni cata- lysts for CO 2 reforming of methane and good results were reported [6,7]. Furthermore, Ni/Ce–ZrO 2 showed high ac- tivity and stability in partial oxidation of methane without catalyst deactivation [8]. Based on the previous results, in the present work, Ce–ZrO 2 -supported Ni catalyst was ap- plied to SRM using a stoichiometric feed mixture (H 2 O/ CH 4 = 1.0) and oxy-steam reforming of methane (OSRM). As a result, it has been found that Ni supported on Ce-doped ZrO 2 is very active and stable in SRM even under severe conditions and exhibits high activity as well as stability in OSRM. 2. Experimental Support materials employed in this study were mon- oclinic ZrO 2 (99%, Strem Chemicals), MgAl 2 O 4 (99%, Johnson Matthey), MgO (99%, Aldrich Chemicals), CeO 2 (99%, Aldrich Chemicals), and Ce-doped ZrO 2 . Ce-doped zirconia support was prepared by the sol–gel method using a mixture of zirconyl chloride and the corresponding salt of Ce [7,8]. The weight ratio of ZrO 2 to CeO 2 was 4 : 1. The modified zirconia support was calcined at 800 ◦ C for 6 h in air. Supported Ni (15 wt%) catalysts were prepared by the molten-salt method using its nitrate source [8,9]. The cata- lyst samples were calcined at 550 ◦ C for 6 h in air. Catalytic activity measurements were conducted in a fixed-bed quartz reactor with inner diameter of 4 mm at atmospheric pres- sure. The reactant gas stream consisted of CH 4 and H 2 O with a molar ratio of 1 : 1 both in SRM and OSRM. The ra- 1011-372X/01/0600-0031$19.50/0  2001 Plenum Publishing Corporation