The issue of tuning the relative height of the first two dehydrogenation barriers of methane (CH4 -> CH3 + H and CH3 -> CH2 + H) is addressed using density-functional theory. It is shown that the combination of a very active reaction center-such as Rh-with a more inert substrate-such as Cu(111)-may hinder the second dehydrogenation step with respect to the first, thus resulting in the reverse of the natural order of the two barriers' heights.