This study has designed and implemented a library of hetero‐nanostructured catalysts, denoted as Pd@Nb2O5, comprised of size‐controlled Pd nanocrystals interfaced with Nb2O5 nanorods. This study also demonstrates that the catalytic activity and selectivity of CO2 reduction to CO and CH4 products can be systematically tailored by varying the size of the Pd nanocrystals supported on the Nb2O5 nanorods. Using large Pd nanocrystals, this study achieves CO and CH4 production rates as high as 0.75 and 0.11 mol h−1 gPd −1, respectively. By contrast, using small Pd nanocrystals, a CO production rate surpassing 18.8 mol h−1 gPd −1 is observed with 99.5% CO selectivity. These performance metrics establish a new milestone in the champion league of catalytic nanomaterials that can enable solar‐powered gas‐phase heterogeneous CO2 reduction. The remarkable control over the catalytic performance of Pd@Nb2O5 is demonstrated to stem from a combination of photothermal, electronic and size effects, which is rationally tunable through nanochemistry.

More than 20 gigatonnes of carbon dioxide are released into the atmosphere every year. The conversion of CO2 into value‐added chemicals and fuels by solar energy is an immediate solution to mitigate CO2 emissions, while providing global energy security. In this work, boron‐ and phosphorus‐doped silicon nanocrystals (ncSi), comprised of three earth‐abundant elements, are investigated for gas‐phase heterogeneous photoreduction of CO2 for the first time. Surface dopants are demonstrated to induce CO2 adsorption capacity. Remarkably, phosphorus‐doped ncSi is found to be the best performer among the singly doped and co‐doped ncSi samples, doubling the rate of pristine ncSi. The enhancement of activity is attributed to the combination of the number of surface hydrides, its surface hydrophobicity, the addition of electronegative surface atoms, and perhaps an enhanced hydridic character of the SiH induced by the n‐doping effect. Significantly, boron and phosphorus dopants are shown to provide increased stability of CO2 reduction activity compared to pristine ncSi after storing the samples in air for 2 weeks. These noteworthy findings open up a pathway to develop sustainable alternatives for existing photocatalysts for CO2 conversion.

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The size dependence of the photothermal effect of palladium nanocrystals enables the selectivity of the solar powered heterogeneous catalytic hydrogenation of carbon dioxide to be finely tailored towards producing either carbon monoxide through the reverse water gas shift reaction, CO 2 + H 2 → CO + H 2 O, favored for small nanocrystals or to methane, via the Sabatier methanation reaction, CO 2 + 4H 2 → CH 4 + 2H 2 O, preferred for larger nanocrystals. This is described by Geoffrey A. Ozin and co‐workers in article number 1700252 .

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