Finely divided supported palladium particles are used as catalysts in many technical processes. Using MAPS we have recently investigated the interaction of hydrogen with the Lindlar catalyst (PdPb/CaCO3) and commercial carbon supported Pd-based catalysts used for the selective hydrogenation of nitro-arenes to amino-arenes. In addition to the presence of the modes of the (expected) hydrogen-in-metal system β-PdH near 500 cm-1, we observed an additional very weak mode at ~2100 cm-1 on Pd(20 wt%)/C and Pd black. In view of their commercial importance, palladium hydrogenation catalysts have been extensively studied for more than 50 years, so the detection of a new catalytic site is very significant. Our experience is that MERLIN has an approximately tenfold advantage in signal-to-noise ratio over MAPS and we wish to use the greater sensitivity of MERLIN to confirm this novel result.