JOURNAL OF CATALYSIS 99, 171-183 (1986) Platinum Catalysts Supported on Activated Carbons I. Preparation and Characterization F. RODR~UEZ-REINOSO,’ I. RODRIGUEZ-RAMOS, C. MORENO-CASTILLA,* A. GUERRERO-RUIZ,* AND J. D. LOPEZ-GONZALEZ? Depnrtnmento de Quimica Inorgrinicu, Uniuersidud de Alicunte. Aliconte. ‘Departumento de Quimicu Inorgdnicu, Uniuersidud de Grunudu. Grtrncrdu, and tDepurttimento de Q~imica Inorgdnka, Uniuersidud Nuciomrl de Edrctucirjn u Distuncitr, Mudrid, Spclin Received November 28, 1984; revised November 25, 1985 Several Pt catalysts supported on activated carbons (manufactured from olive stones and almond shells) have been prepared with both H2PtC16 6Hz0 and [Pt(NH&]C12 as metal precursor and using different methods. Once reduced, the supported catalysts were characterized by Hz and CO chemisorption as well as X-ray diffraction and transmission electron microscopy. The effect of reduction conditions on metal dispersion has been studied and correlated with the surface proper- ties of the supports. The results show that porosity with sizes ranging from 9 to 11 nm is decisive for obtaining a high Pt dispersion. To increase the dispersion of the catalysts prepared from [Pt(NH,).JC12 a treatment with He prior to reduction of the catalysts in Hz seems to be essential in order to avoid the formation of an unstable hydride which leads to agglomeration of the Pt parti- CkS. 0 1986 Academic Press, Inc. INTRODUCTION Although most of the supports used in heterogeneous catalysis are oxides such as SiOZand A&O3 there is a growing interest in using carbons, especially activated car- bons, as supports because they are rela- tively inexpensive and have a large surface area and a low intrinsic catalytic activity. However, although carbon is becoming a commercial support of growing interest, es- pecially for Group VIII metals in hydroge- nation reactions (I), most of the carbon- supported catalysts are prepared at the laboratory level (2). Much still needs to be done to explore the preparation of carbons with large textural differences in order for them to be used as supports for new cata- lysts. For instance, by relating the surface properties of the carbon with the supported metal dispersion it will be possible to design ’ Author to whom correspondence should be ad- dressed. catalysts with different catalytic activities (3). In this sense, Walker and co-workers (4-7) have shown that, for Pt supported on a graphitized carbon black, the increase in surface area and heterogeneity of the Cal-- bon leads to a larger Pt dispersion. On the other hand, the pore size distribu- tion of the carbon may condition the diffu- sion of reactants and products, changing the activity and selectivity of the catalyst; thus, certain molecular sieve carbons have been used as catalyst supports to control the product distribution of the reaction (8- 11). One of the problems found when using activated carbons as catalyst supports is their large ash content which, after the acti- vation process, is concentrated on their surface (4); these inorganic constitutents may interact with the metal, affecting its catalytic activity and sintering resistance (f2) and even catalyzing secondary reac- tion. With this in mind, we have been de- veloping in the last few years a series of 171 002 1-95 17186 $3 .OO CopyrIght 0 1986 by Academic Press. Inc. All rights of reproducfwn m any form reserved.