The formation of monovalent palladium in PdNaK-clinoptilolite where Pd(II) is introduced into extraframework sites as [Pd(NH3)(4)](2+) by liquid-state ion exchange at 298 K, is compared to that observed in PdH-clinoptilolite where Pd(II) is incorporated by solid-state ion exchange at 823 K, using electron spin resonance (ESR) and electron spin-echo modulation (ESEM) spectroscopies. Dehydration at 473 K produces one Pd(I) species in PdH-clinoptilolite but no ESR signal in PdNaK-clinoptilolite. This indicates that the stability of Pd(I) between PdH-clinoptilolite and PdNaK-clinoptilolite is different, probably due to the different locations and environments of Pd in these systems. Hydrogen reduction of Pd(II) in these two materials after activation reveals that Pd(II) ions in PdNaK-clinoptilolite occupy relatively accessible sites in comparison to those in PdH-clinoptilolite. The interactions of Pd(I) formed by thermal reduction of PdH-clinoptilolite with various adsorbates are also studied. The ESR studies coupled with ESEM measurements show that Pd(I) in PdH-clinoptilolite interacts rapidly with molecules smaller than methanol, such as hydrogen, water, ammonia, and carbon monoxide, and forms a stable complex with them. However, adsorption of benzene and pyridine on thermally reduced PdH-clinoptilolite produces no ESR signal due to a Pd(I)-benzene complex or a Pd(I)-pyridine complex, suggesting that Pd(I) is located at a site in eight-ring channels where benzene and pyridine are too big to enter.