Adsorbate interactions of paramagnetic palladium(I) species in Pd(II)-exchanged Na-MCM-22 zeolite are studied by electron spin resonance (ESR) and electron spin-echo modulation (ESEM) spectroscopies. Oxidation and subsequent evacuation at 825 K of Na-MCM-22 zeolite exchanged with Pd(NH3)(4)Cl-2 results in the formation of a Pd(I) species. Monovalent palladium can be produced in PdNa-MCM-22 material by room temperature hydrogen reduction after dehydration and O-2 treatment at high temperature. Addition of hydrogen to PdNa-MCM-22 after dehydration, O-2 treatment, and evacuation (activation) is found to increase the concentration of Pd(I) at room temperature and at higher temperature is found to reduce Pd(I) to Pd(0)(n) (palladium clusters). Adsorption of O-2 and H2O to an activated sample containing Pd(I) generates a Pd(II)-O-2(-) species with g(perpendicular to) > g(parallel to). Adsorption of CO on an activated sample results in a Pd(I)-(CO)(2) complex which partially transforms to Pd(I)-CO on evacuation. Adsorption of ethylene on an activated sample produces Pd(I)-C2H4 and Pd(I)-C4H8 complexes, suggesting that Pd(I) catalyzes dimerization of ethylene. Methanol and ethanol behave differently when adsorbed on an activated sample. While methanol reduces Pd(I) to Pd(0)(n) at room temperature, ethanol forms a palladium complex suggested to be Pd(I)-CH3CH2OD. Adsorption of ammonia on activated PdNa-MCM-22 leads to two Pd(I)-(ND3)(1) complexes, probably in different environments. On the other hand, adsorption of pyridine results only in a single species, perhaps due to steric effects. The kinetic size of the adsorbates plays a major role in forming complexes with Pd(I) in MCM-22 zeolite. A significant amount of Pd(I) formed during activation is located in sites inaccessible to relatively large molecules while it reacts immediately with smaller adsorbates.