Isotope heat effect in reactions involving hydrogen evolution on palladium catalyst particles

The heat effect in the reduction of copper(II) by formaldehyde on palladium catalyst particles accompanied by hydrogen evolution depends on the presence of deuterium in the system. In the case of 80% substitution of hydrogen in the system by deuterium the heat effect increases 1·5 times. This fact can not be attributed only to the difference in the energies of the bonds of hydrogen and deuterium in compounds participating in the reaction.