296
Ind. Eng. Chem. Prod. Res. Dev. 1981, 20,296-300
McMahon, R. F. J. fharm. Sci. 1966, 55, 457. Pool, 0.L. J . Cancer Res. Clin. Oncol. 1979, 93, 215. Pool, 9. L. J . Cancer Res. Clin. Oncol. 1979, 93, 221. Gescher. A.; Hlckman, J. A.; Simmonds, R. J.; Stevens, M. F. G.; Vaug h n , K. Tetrahedron Lett. 1978, 50, 5041. (88) Axekod, J.; Cochin, J. J . pharm. Exp. Ther. 1957, 121, 107. (89) Leadbeater, L.; Davies, D. R. Biochem. fharmacoi. 1964, 13, 1569. (90) Vaughan, K.; Stevens, M. F. G. Chem. SOC.Rev. 1978, 7 , 377. (84) (85) (86) (87)
(91) Julliard, M.; Vernin, G. work in progress. (92) White, H.; Maskill, H.; Woodcock, D. J.; Shroeder, M. A. Tehahedron Lett. 1969, 21, 1713. (93)Connors, T. A.; Hare, J. R. Biochem. fharmacol. 1975. 24. 2133.
Received for review October 6 , 1980 Accepted January 21, 1981
CATALYST SECTION Nickel-Support Interactions: Their Effects on Particle Morphology, Adsorption, and Activity Selectivity Properties Calvin H. Bartholomew," Rlchard B. Pannell, Jay L. Butler, and Donald G. Mustard Depadmenf of Chemical Engineering, Brigham Young University, Provo, Utah 84602
The adsorption and CO hydrogenation activity/selectivity properties of well-characterized Ni/Si02, Ni/AI2O3,and Ni/Ti02 catalysts were investigated. Electron micrographs reveal evidence of three-dimensional metal clusters in Ni/SiOz and Ni/AI2O3 and twodimensional, raft-like particles in Ni/Ti02. The stoichiometries of H2 and CO adsorptions on nickel are affected by particle size and metal-support effects: for example, hydrogen adsorption on welldispersed Ni/AIz03 and on Ni/Ti02 occurs with less than one hydrogen atom per surface nickel atom, and the CO/M adsorption ratio on Ni/AI2O3increases with decreasing metal loading and metal particle size. The effects of support and crystallie size in the hydrogenation of CO are evident from significant changes in methanation activii and selectivity for methane and C2+ hydrocarbons. Activity and selectivity for production of C2+ hydrocarbons is increased by strong metal support interactions. There is an apparent, welldefined correlation between increasing yield of higher molecular weight hydrocarbons and increasing CO/H adsorption ratio with increasing metal dispersion in both Ni/AIzO3 and Ni/Si02 systems.
Introduction Effects of support and metal crystallite size on adsorption and activity/selectivity properties of nickel were reported nearly two decades ago (O'Neill and Yates, 1961; Taylor et al., 1964). Recent studies provide evidence that crystallite size effects and metal-support interactions markedly influence Hzand CO adsorption on nickel as well as activity/selectivity properties of nickel in CO hydrogenation (Vannice, 1976; Bhatia et al., 1978; Vannice and Garten, 1979; Bartholomew and Pannell, 1980; Bartholomew et al., 1980). The present study was undertaken to determine effects of metal dispersion and support on nickel crystallite morphology, H2and CO adsorption on nickel, and activity/selectivity properties in CO hydrogenation on nickel. Our primary objective was to establish relationships among physical, chemical, and catalytic properties of supported nickel catalysts, especially between crystallite size and support effects. This paper reports the results of a comprehensive investigation of nickel on alumina, silica, and titania by means of transmission electron microscopy (TEM), X-ray diffraction (XRD), Hzand CO adsorption, and CO hydrogenation reaction studies. Experimental Section Materials. Hydrogen and nitrogen gases (99.99%, Whitmore) were simultaneously purified using a Pd Deoxo catalyst (Engelhard) followed by a Molecular Sieve 5A (Linde) trap. CO (99.99%, Matheson) was also passed 0196-4321/81/1220-0296$01.25/0
through a molecular sieve trap to remove iron carbonyl. Alumina, silica, and titania-supported catalaysts (with the exception of four samples described below) were prepared by impregnation with a Ni(N03)2solution to incipient wetness according to procedures described previously (Bartholomew et al., 1980). Two other silica-supported catalysts, a 2.9% Ni/Al2O3and a 2.8% Ni/TiOz, were prepared by means of a controlled pH precipitation technique described by van Dillen at al. (1976) using the same alumina, silica, and titania. All of these samples were also dried 24 h at 373 K and subsequently reduced at 725 K according to procedures previously described (Bartholomew and Farrauto, 1976; Bartholomew et al., 1980). Percent nickel loadings were determined for most of the catalysts by Rocky Mountain Geochemical Corporation using atomic absorption spectroscopy. Apparatus and Procedure. Chemisorption Measurements. Gas adsorption measurements were carried out in a conventional Pyrex glass volumetric adsorption apparatus previously described (Bartholomew, 1977). Measurement of total Hzuptake at 298 K and irreversible CO uptake at 190 and 273 K were also described previously (Pannell et al., 1977); Bartholomew and Pannell, 1980). The accuracy of the adsorption measurements was generally *lo%. Calculations of dispersion and average metal crystallite size for supported nickel were discussed previously (Bartholomew and Pannell, 1980). Extent of reduction to the metal was determined for Ni/Al2O3and Ni/SiOpcatalysts by O2titration at 723 K and for Ni/TiOz 0 1981 American
Chemical Society
Ind. Em. chem.Rod. Res. Dev.. Vd. 20, No. 2. 1981 287
Table I. Average CrJratallite Diametem (nm) for Ni/AI,O,, Ni/SiO, and Ni/TiO, Catalysts TEM~
catalyst 14% Ni/AI,O, 23% 2.7% NilSiO, 3.6% 13.5% 15% 2.8% Ni/TiO, 15% 15%
pretreatment fresh sintered, 7 2 h a t 1023 K i n H, fresh
fresh
freshd freshd fresh fresh fresh sintered, 3 h a t 1023 Kin H,
d,,
H, ads" 5.6 10
ds
dv
3.7
4.6 12
10
6.3 1.9 2.6 2.4 5.1 8.7 23 1000
6.0 2.9 2.7 2.9 8.1 5.5 10 32
6.4
.. -
-
9.4
..
12 35
dv, XRD'
