Or just chemically changed to a point of being depleted during reaction?
In LENR reactions there is only a small reduction in mass of the lattice host metal, sometimes attributed to nuclear collisions and transmutations.
By using nanoscale material, the adsorption of Hydrogen is faster and there is more hydrogen per surface area. These reactions occur in the bulk relatively close to the surface, so at nanoscale there is much better chance of hydrogen reactions running into each oTHER when the particle is that small.
No...it is the hydrogen isotope that is consumed. Some very infinitesimal amount may be transmuted by side processes. Most likely effect on the metal substrate is that its "crystal" structure is changed to the extent that it no longer functions to hold the deuterium "correctly" for the hydrogen reaction to occur.