Catalysis on ruthenium clusters supported on CeO2 or Ni-doped CeO2: Adsorption behavior of H-2 and ammonia synthesis

被引:60
作者
Izumi, Y
Iwata, Y
Aika, K
机构
[1] Department of Environmental Chemistry and Engineering, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku
关键词
D O I
10.1021/jp952602o
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Catalysis on Ru clusters supported on CeO2 or Ni-doped CeO2 was investigated. RU(3)(CO)(12) was reacted with CeO2, followed by heating in vacuum at 673 (i) or 813 K (ii) and then in H-2 at 588-1073 K (T-H2). Activities of both catalysts had the T-H2 dependence, which has a maximum at T-H2 = 873 K for ammonia synthesis. The rates on i were faster than those on ii by a factor of 2.0-1.1 in the range of T-H2 = 588-973 K. On a sample in which Ru-3(CO)(12) was supported on previously reduced Ni/CeO2 (in H-2 at 773 K) iii, the highest synthesis rate was 1.5 x 10(-3) mol h(-1) g(cat)(-1) at T-H2 = 588 K on iii. The activity order iii > i > ii can be understood in terms of two factors: (A) reduction extent of support and (B) number of active Ru sites. The two factors conflicted with each other when the treatment temperature in H-2 increased. By heating the samples in H-2 up to 873 K to satisfy factor A, the aggregation of Ru clusters for i or physical blocking of surface Ru sites by CeO2-x for ii occurred: factor B was not satisfied. The two factors should be optimized in catalyst iii, where the support cerium oxide was thoroughly reduced through the doped Ni. On reduced Ni/CeO2, the Ru cluster implantation can be done at low temperature (588 K). Obtained values of r(Ru-Ru) at 2.62 Angstrom (N = 7.1) and r(RU)-(O(S)) (O(s) is the oxygen atom at surface) at 2.12 Angstrom (N = 1.2) by EXAFS for Ru-3-Ni/CeO2 suggested a flat Ru cluster model comprised of several Ru atoms on reduced Ni/CeO2-x surface. The H(a)/Ru-total ratio exceeded unity for catalysts i and iii, suggesting new H adsorption sites. The temperature-programmed desorption for hydrogen (simultaneous desorption of HD and D-2 for iii at 330-430 K suggested that the H at the new site and H on Ru surface were exchangeable above 330 K. The ''reservoir'' effect of the new site for H on catalysis is discussed in relation to new kinetic design of hydrogenation catalyst.
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页码:9421 / 9428
页数:8
相关论文
共 19 条
[1]   SUPPORT AND PROMOTER EFFECT OF RUTHENIUM CATALYST .3. KINETICS OF AMMONIA-SYNTHESIS OVER VARIOUS RU CATALYSTS [J].
AIKA, K ;
KUMASAKA, M ;
OMA, T ;
KATO, O ;
MATSUDA, H ;
WATANABE, N ;
YAMAZAKI, K ;
OZAKI, A ;
ONISHI, T .
APPLIED CATALYSIS, 1986, 28 (1-2) :57-68
[2]   MICROSTRUCTURAL AND CHEMICAL-PROPERTIES OF CERIA-SUPPORTED RHODIUM CATALYSTS REDUCED AT 773-K [J].
BERNAL, S ;
BOTANA, FJ ;
CALVINO, JJ ;
CAUQUI, MA ;
CIFREDO, GA ;
JOBACHO, A ;
PINTADO, JM ;
RODRIGUEZIZQUIERDO, JM .
JOURNAL OF PHYSICAL CHEMISTRY, 1993, 97 (16) :4118-4123
[3]   INTERACTION OF HYDROGEN WITH SUPPORTED RU CATALYSTS - HIGH-PRESSURE IN-SITU NMR-STUDIES [J].
BHATIA, S ;
ENGELKE, F ;
PRUSKI, M ;
GERSTEIN, BC ;
KING, TS .
JOURNAL OF CATALYSIS, 1994, 147 (02) :455-464
[4]   A SPECTROSCOPIC CHARACTERIZATION OF THE REDUCTION OF CERIA FROM ELECTRONIC-TRANSITIONS OF INTRINSIC POINT-DEFECTS [J].
BINET, C ;
BADRI, A ;
LAVALLEY, JC .
JOURNAL OF PHYSICAL CHEMISTRY, 1994, 98 (25) :6392-6398
[5]   ACCURATE REDETERMINATION OF STRUCTURE OF TRIRUTHENIUM DODECACARBONYL, RU3(CO)12 [J].
CHURCHILL, MR ;
HOLLANDER, FJ ;
HUTCHINSON, JP .
INORGANIC CHEMISTRY, 1977, 16 (10) :2655-2659
[6]   INDUCED CHANGES IN CERIA BY THERMAL TREATMENTS UNDER VACUUM OR HYDROGEN [J].
FIERRO, JLG ;
SORIA, J ;
SANZ, J ;
ROJO, JM .
JOURNAL OF SOLID STATE CHEMISTRY, 1987, 66 (01) :154-162
[7]   A LEED-IV INVESTIGATION OF THE RU(001)-P(2 X 1)-H STRUCTURE [J].
HELD, G ;
PFNUR, H ;
MENZEL, D .
SURFACE SCIENCE, 1992, 271 (1-2) :21-31
[8]  
IZUMI Y, 1994, CHEMTECH, V24, P20
[9]   PROMOTED CATALYSIS BY SUPPORTED [RU6N] CLUSTERS IN N-2 AND/OR H-2 - STRUCTURAL AND CHEMICAL CONTROLS [J].
IZUMI, Y ;
AIKA, K .
JOURNAL OF PHYSICAL CHEMISTRY, 1995, 99 (25) :10346-10353
[10]   ADSORBED HYDROGEN EFFECT ON THE ADSORPTION AND REACTIVITY OF N-2 MOLECULES ON RU/MGO AND RU-CS+/MGO - HYDROGEN DIPOLE EFFECT ENHANCED BY DOPED CS+ [J].
IZUMI, Y ;
HOSHIKAWA, M ;
AIKA, K .
BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN, 1994, 67 (12) :3191-3200