[Pd(NH3)(4)](2+)-exchanged sepiolite clay (Pd-sepiolite) has been applied to the catalytic Suzuki-type carbon-carbon coupling reactions of 4-bromophenol with phenylboronic acid or sodium tetraphenylborate in water. The Pd-sepiolite effectively catalyzed the reaction under mild reaction conditions (at room temperature in air). The Pd-sepiolite system exhibits higher yield than unsupported Pd(II) salts, [Pd(NH3)(4)]Cl-2-impregnated SiO2 (Pd-SiO2), and a commercially available Pd/C consisting of Pd metal particles. The structure of Pd species in the catalysts before and after the reaction was well characterized by a combination of XRD, TEM, UV-Vis, Pd K -edge XANES/EXAFS, and Pd L-III-edge XANES. XAFS and TEM results confirmed the formation of metal particles after the reaction by unsupported Pd(II) salt and Pd-SiO2. In contrast, for Pd-sepiolite the change in the structure of Pd species after the reaction was not significant; the highly dispersed Pd(II) complex, present before the reaction, was still the main Pd species together with the small Pd clusters (2-7 nm) as minor species. As a result of the high stability, Pd-sepiolite was reused without losing its activity. Significantly high turnover numbers (TON = 940,000) were also attained at reflux temperature. It is suggested that Pd metal precipitation during the reaction is inhibited by a strong electrostatic interaction of sepiolite with Pd(II) species. (C) 2004 Elsevier Inc. All rights reserved.