JOURNAL OF CATALYSIS 67, 186-206 (1981) Determination of Metal Crystallite Size and Morphology in Supported Nickel Catalysts DONALD G. MUSTARD AND CALVIN H. BARTHOLOMEW Catalysis Laboratory, Department of Chemical Engineering, Brigham Young University, Provo, Utah 84602 Received May 8, 1980; revised July 7, 1980 The application of H2 chemisorption, X-ray diffraction (XRD) line broadening, and transmission electron microscopy (TEM) to the determination of metal crystallite size and size distribution in Ni/SiO*, Ni/AlZ03, and Ni/TiO, catalysts having wide ranges of nickel loadings and dispersions was investigated. Average crystallite diameters estimated from HZ chemisorption and TEM were found to be in very good agreement over wide ranges of metal dispersion and loading in the Ni/SiO, system and in good agreement for a 15% Ni/Al,O,; poor agreement was evident in the Ni/TiO, system, the results suggesting that H2 adsorption was suppressed. In the few samples where it was possible to obtain information from XRD, the estimates of crystallite diameter were generally in good or fair agreement with those from HZ chemisorption or TEM. The specific limitations of these three techniques in determination of nickel crystallite size and their application to the study of sintering and metal support interactions in supported nickel catalysts are presented and discussed. INTRODUCTION Nickel catalysts find application in a number of important industrial processes, for example, hydrogenation of unsaturated organics, steam reforming, and methana- tion. Therefore, determination of their physical properties is of considerable prac- tical value. Nickel metal particle size is one of the most important properties, since it is a measure of metal dispersion, i.k., the number of surface sites available in the catalyst for promoting the reaction. Since in industrial applications, metal particle size and metal surface area change with time because of catalyst degradation (i.e., sintering, poisoning, and coking), the mea- surement of these properties as a function of time for a real or simulated process during or after catalyst failure reveals the rate, extent, and nature of the degradation process, Accordingly, it is important to know how degradation processes and cata- lyst properties such as metal dispersion, metal concentration, and extent of reduc- tion to the metal might affect the measure- ment of metal particle size. Previous studies of metal particle size and various methods for estimating this property have been summarized and dis- cussed in reviews by Dorling (I), Whyte (2), and Farrauto (3). Farrauto discussed the Group VIII metals individually, indicating what he considered to be the best methods for studying these metals. In the case of nickel, he mentioned that H, chemisorption was most commonly used although X-ray diffraction (XRD) and transmission elec- tron microscopy (TEM) were also consid- ered useful techniques. It is also clear from recent literature that magnetic susceptibil- ity measurements can also be used to mea- sure nickel crystallite size and size distribu- tion (4-6). Farrauto pointed out, however, that a combination of at least two methods is essential for accurate determination of metal particle size for a given catalyst sys- tem and that work defining the limitations of various techniques for measuring metal particle size and metal surface area had not yet been reported in the case of supported nickel. Indeed, a careful search of more recent literature reveals that no such definitive work has yet appeared. Moreover, except for two very recent studies (6, 7) the use of 186 0021-9517/81/010186-21$02.00/O Copyright @ 1981 by Academic Press. Inc. AU rights of reproduction in any form reserved.