Coaxing unreactive sites Optical excitation of localized surface plasmon resonances can confine light and create electromagnetic (EM) “hotspots” that can increase catalytic reaction rates. Sytwu et al. show how optical excited plasmons can also control the location of the active site. A crossed-bar gold-palladium hydride (Au-PdH _x ) plasmonic antenna-reactor system localized EM radiation away from the more reactive PdH _x tips. Using in situ environmental transmission electron microscopy, the authors show that changing the illumination wavelength and intensity, along with the surrounding hydrogen gas pressure, could shift dehydrogenation away from the sharp PdH _x nanorod tips to the flat middle faces. Science , this issue p. 280