RESUMO
Many highly active electrocatalysts for the reduction of N2 to NH3 (NRR) have been synthesized but suffer from poor selectivity. One crucial reason is that the adsorption of hydrogen often dominates at the active centers at applied voltage, which leads to the competitive hydrogen evolution reaction. This work used density functional theory (DFT) calculations to develop a class of stable polyoxometalate-based electrocatalysts including phosphomolybdic-, phosphotungstic-, silicotungstic-, and silicomolybdic-acid supported Ru single atoms to efficiently catalyze the NRR process with an overpotential lower than 0.25 V. More importantly, phosphomolybdic- and phosphotungstic acid-supported Ru electrocatalysts can achieve high selectivity at applied voltage. This work offers useful insights into designing high-performance polyoxometalate-based electrocatalysts for the NRR.
RESUMO
Since the discovery that ceria is an active catalyst for selective hydrogenation of alkynes, there has been much debate on the catalytic mechanism. In this work, we propose, based on density functional theory (DFT) investigations, a mechanism that involves the heterolytic dissociation of H2 at oxygen vacancies of CeO2(111), facilitated by frustrated Lewis pairs consisting of spatially separated O and Ce sites. The resulting O-H and Ce-H species effectively catalyze the hydrogenation of acetylene, avoiding the overstabilization of the C2H3* intermediate in a previously proposed mechanism. On the basis of our mechanism, we propose the doping of ceria by Ni as a means to create oxygen vacancies. Interestingly, the Ni dopant is not directly involved in the catalytic reaction, but serves as a single-atom promoter. Experimental studies confirm the design principles and demonstrate much higher activity for Ni-doped ceria in selective hydrogenation of acetylene. The combined results from DFT calculations and experiment provide a basis to further develop selective hydrogenation catalysts based on earth-abundant materials.
RESUMO
CO oxidation on phosphomolybdic acid (H3PMo12O40, PMA) supported single-metal atom (M = Pt, Au, Co, Cu, Fe, Ir, Ni, Os, Pd, Ag, Rh, and Ru) (M-PMA) catalysts is studied by density-functional-theory (DFT) calculations. Adsorption of CO and O2 on M-PMA is investigated. Based on electronic structure analysis, O2 is activated by the single-metal-atom active center. The Langmuir-Hinshelwood mechanism is systematically explored for CO oxidation on M-PMA, and it is found that M-PMAs have high reactivity toward CO oxidation. The Mars-van Krevelen mechanism is also investigated and it is shown to be less likely to be responsible. Our DFT findings will provide useful insight for designing stable, highly active heteropolyacid-supported single-metal-atom catalysts.
RESUMO
Single-atom catalysts (SACs) have recently been shown to have high performance in catalyzing the synthesis of NH3 from N2. Here, we systematically investigated a series of single transition metal atoms anchored on stepped CeO2 (CeO2-S) to screen the potential electrocatalysts for a N2 reduction reaction (NRR) via density functional theory computations. We first demonstrated that these SACs are stable via large calculated binding energies. Second, we evaluated the adsorption of *N2 over CeO2-S-supported single atoms. Here, those systems that can activate N2 molecules were selected as candidates. We then showed that CeO2-S-supported single Mo and Ru atoms have high catalytic activity for NRR via low limiting potentials of -0.52 and -0.35 V, respectively. Meanwhile, the competitive hydrogen evolution reaction is highly suppressed over these two SACs because the adsorption of *N2 is prior to *H. Finally, the origin of the NRR activity over these SACs was investigated. This work offers useful insights into designing high-performance CeO2-based electrocatalysts for NRR.