Abstract
Photocatalysis has not found widespread industrial adoption, in spite of decades of active research, because the challenges associated with catalyst illumination and turnover outweigh the touted advantages of replacing heat with light. A demonstration that light can control product selectivity in complex chemical reactions could prove to be transformative. Here, we show how the recently demonstrated plasmonic behaviour of rhodium nanoparticles profoundly improves their already excellent catalytic properties by simultaneously reducing the activation energy and selectively producing a desired but kinetically unfavourable product for the important carbon dioxide hydrogenation reaction. Methane is almost exclusively produced when rhodium nanoparticles are mildly illuminated as hot electrons are injected into the anti-bonding orbital of a critical intermediate, while carbon monoxide and methane are equally produced without illumination. The reduced activation energy and super-linear dependence on light intensity cause the unheated photocatalytic methane production rate to exceed the thermocatalytic rate at 350 °C.
Highlights
Photocatalysis has not found widespread industrial adoption, in spite of decades of active research, because the challenges associated with catalyst illumination and turnover outweigh the touted advantages of replacing heat with light
The effects of light-emitting diodes (LEDs) intensity and photon energy on the reaction rates using the Rh photocatalyst were carefully studied by varying the output power and wavelength of the light source
Under ultraviolet illumination near B1 W cm À 2, the photoreaction rate under H2-rich conditions changed from a linear to a super-linear dependence on light intensity (RphotopIn, n 1⁄4 2.1 at 623 K and 2.4 at 573 K, Fig. 2c)
Summary
Photocatalysis has not found widespread industrial adoption, in spite of decades of active research, because the challenges associated with catalyst illumination and turnover outweigh the touted advantages of replacing heat with light. By tuning photon and LSPR energies so that hot carriers are injected into specific anti-bonding orbitals of specific reaction intermediates, product selectivity may be achieved[26,36,37] These early demonstrations of plasmonic photocatalysis either featured intense laser pulses (BkW cm À 2) on nanoparticle clusters to generate high concentrations of hot carriers[14,16,17,18], or they used alloyed or hybrid nanostructures composed of plasmonic (gold, silver, aluminium) and catalytic (platinum, cobalt, palladium) metals[20,21,26,27,28]. We observe that mild illumination of the Rh nanoparticles reduces activation energies for CO2 hydrogenation B35% below thermal activation energies, it purnoddeurciellsuamsintraotniognsferloecmtivliotwy -tionwteanrsdistyC(HB4Wovcemr CÀO2)., continuous wave blue or ultraviolet light-emitting diodes (LEDs), the photocatalytic reactions on unheated Rh nanoparticles produce
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