With a hydrogen-sensitive Pd metal-oxide-semiconductor structure we have investigated how Ag overlayers affect the hydrogen adsorption and desorption properties of Pd. By varying the concentration of Ag in the top layer, we have continuously changed the distribution of d states close to the Fermi energy as determined by photoemission. For moderate amounts of Ag, only blocking of active hydrogen sites on the Pd surface occurs and no effects due to the variation in the electronic density of states can be detected.