Journal of Catalysis 209, 355–364 (2002) doi:10.1006/jcat.2002.3637 Properties of Carbon-Supported Platinum Catalysts: Role of Carbon Surface Sites M. A. Fraga, ∗,1 E. Jord ˜ ao, ∗ M. J. Mendes, ∗,2 M. M. A. Freitas,† J. L. Faria,† and J. L. Figueiredo† ,2 ∗ Laborat ´ orio de Desenvolvimento de Processos Catal´ ıticos, UNICAMP/FEQ/DESQ, C.P. 6066, 13083-970 Campinas, S.P., Brazil; and †Laborat ´ orio de Cat ´ alise e Materiais, Departamento de Engenharia Qu´ ımica, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal Received October 30, 2001; revised April 8, 2002; accepted April 11, 2002 The effect of oxidation treatments of the support on the prop- erties of carbon-supported platinum catalysts has been analyzed. A set of activated carbon carriers has been prepared by oxidative treatments of a commercial carbon in liquid as well as in gas phase. The carbons obtained had largely identical pore structures but dif- fered considerably in their surface chemistry as shown, for example, by their point of zero charge (PZC) values. The catalysts were pre- pared by equilibrium impregnation of the supports with an aqueous solution of hexachloroplatinic acid. N 2 adsorption, TPD, XPS, TPR, and H 2 chemisorption were used to characterize the supports and the catalysts. The Pt load of the catalysts was found to depend on the PZC of the supports. However, the Pt dispersion was found to depend on the total surface oxygen content of the supports. These results were rationalized by the assumption that the surface basic groups of the supports are anchoring sites for the strong adsorption of platinum. c  2002 Elsevier Science (USA) Key Words: activated carbon; oxidative treatments; platinum catalysts; strong adsorption; surface basic sites. INTRODUCTION Activated carbons are frequently used as catalyst sup- ports in the fine chemical industry owing to their specific features: they are stable in both acid and basic media and carbon can be burnt off, allowing an economical and eco- logical effective recovery of the precious catalytic metal (1, 2). It is well known that the interaction of the active phase with the support can be modified by pretreatment of the support. There is consequently in the published lit- erature a growing awareness of the need to consider the surface chemistry of carbon supports to achieve adequate catalyst performance (1, 2). The catalytic behavior of acti- vated carbon-supported noble metal catalysts can be mod- ified by oxidation treatments of the support prior to metal loading (2). Different oxidizing treatments, both in the gas and in the liquid phase, can be used to perform chemical 1 Now at INT, Rio de Janeiro, R.J., Brazil. 2 To whom correspondence should be addressed. E-mail: mendes@ desq.feq.unicamp.br and jlfig@fe.up.pt. surface modifications of activated carbons. There is an ex- haustive literature dealing with the nature of the oxygen groups thus formed on the surface of carbon and with their influence upon the properties of carbon-supported catalysts (1). It is now generally accepted that the presence of surface oxygen groups decreases the hydrophobicity of the carbon, thus making its surface more accessible to the metal pre- cursor during the impregnation with aqueous solution (1). On the other hand, the presence of such surface oxygen groups alters the pH values of aqueous carbon slurries and can thus have a considerable influence on the impregnation step of the catalyst preparation (3, 4). Furthermore, these oxygen surface groups are frequently credited with acting as nucleation centers for the generation of highly dispersed metallic crystallites (2). In the near future, the use of carbon materials as cata- lyst supports for precious metals may increase, due to the rapidly advancing development of fuel cells (5). In addi- tion, the use of new carbon materials as industrial catalyst supports may develop rapidly with new interesting carbon materials emerging and becoming available on a commer- cial scale. It is thus important to achieve better basic under- standing of the carbon support material and of the catalysts made there from (2). The present work aims at contributing to the further un- derstanding of the role of carbon oxygen surface groups on the properties of the carbons themselves and of the carbon- supported platinum catalysts prepared by impregnation. EXPERIMENTAL Pretreatment of carbon. A commercial activated carbon (NORIT ROW 0.8s) was used as the starting material. To eliminate some mineral impurities commonly found in ac- tivated carbons, such as Mg, Al, K, Ca, and Fe, the commer- cial sample was extracted for 14 h with 2 mol/L hydrochloric acid at boiling temperature. Subsequently, the sample was washed with distilled water until it reached constant pH and was dried in an oven at 383 K overnight. This sample is denoted as C1. 355 0021-9517/02 $35.00 c  2002 Elsevier Science (USA) All rights reserved.