Photocatalysis shows a great potential for N2 fixation to NH3 under mild conditions, which intrigues increasing research attention in recent decades. To this end, the design of efficient photocatalysts is the key. Herein, we report the synthesis of single atom Ru decorated TiO2 nanosheets rich in oxygen vacancies. Single Ru sites greatly promoted photoreduction of aqueous N2 to NH3, affording an NH3 formation rate of 56.3 μg/h/gcat. We found that isolated Ru atoms likely weakened the hydrogen evolution, promoted absorption of N2, and also improved the charge carrier separation, which led to enhanced N2 photofixation.
The chemical microenvironment modulation of active sites holds promise for facilitating their catalytic performance. Herein, single-atom Ru anchored by ZrSBA-15 modified with diverse organic amine groups has been fabricated and enabled CO2 hydrogenation to produce formic acid (FA) under mild conditions. However, the reaction cannot be achieved without the modification of organic amines. The functional groups as the microenvironment around Ru active sites effectively regulated the activity, in which Ru encapsulated in ZrSBA-15 bearing –NH2 groups exhibited the highest activity, with turnover number (TON) and turnover frequency (TOF) values of 505 and 64 h–1, respectively. Both characterization and experimental results validated that the functional group manipulated the adsorption capacity of the reactant, the electronic state of Ru and hydrophilicity/hydrophobicity of the materials, and thus the catalytic performance.
Lignin-based guaiacol and its derivatives can be hydrogenated to synthesize 2-methoxycyclohexanols (2-MCHs), widely used in the pharmaceutical industry, while the efficient catalytic conversion of guaiacols into 2-MCHs is challenging due to the interference of the side reaction of CAr-OCH3 bond cleavage. In this work, highly selective hydrogenation of various guaiacyl lignin-derived phenols to 2-MCHs (yields of 86%-97%) was realized over a single-atom Ru-based catalyst (Ru1/o-CeO2-ov) that preferentially exposes the CeO2(111) plane and has abundant oxygen vacancies. Control experiments and mechanism studies expounded that Ru-O-Ce is the active site for hydrogenation of aromatic ring in guaiacols, and the exposed (111) plane and abundant oxygen vacancies of ceria can reduce the activation energy of aromatic ring hydrogenation, thereby enabling guaiacols to generate the corresponding hydrogenated products with high selectivity. Response surface optimization experiments indicated that temperature and time have relatively more significant effects on the 2-MCH yield. Moreover, the Ru1/o-CeO2-ov catalyst exhibited excellent reusability, and was extensively applicable to the hydrogenative dearomatization of different types of lignin-derived phenols, providing a unique solution for upgrading biomass feedstock into specific structural chemicals.
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