Tuning the compositions and structures of Pdbased nanomaterials and their supports has shown great potentials in facilitating the sluggish ethanol oxidation reaction (EOR) in alkaline direct ethanol fuel cells. Accordingly, a facile solvothermal method involving Cu and Pd composition migrations is developed in this study, to synthesize highly uniform and small-sized nanospheres (NSs) possessing the special structures of composition-graded (CG) Cu 1 Pd 1 and surface-doped (SD) Ir 0.03 , which are evenly anchored onto N-doped porous graphene (NPG) as a highperformance EOR electrocatalyst ( CG Cu 1 Pd 1 / SD Ir 0.03 NSs/ NPG). Comprehensive physicochemical characterizations, electrochemical analyses, and first-principles calculations reveal that, benefiting from the NPG-imparted mass-transfer and oxygen-reduction effects, the CG−SD structural and sizemorphology effects of the NS, as well as the Cu-and Ir-induced bifunctional, geometric, and ligand effects, CG Cu 1 Pd 1 / SD Ir 0.03 NSs/NPG exhibits not only ultrahigh electrocatalytic activity and highly efficient noble-metal (NM) utilization, showing 7105 and 6685 mA mg −1 in Pd-and NM-mass-specific activity (MSA), respectively, which are 15.8 and 14.9 times those of commercial Pd/C, but also satisfactory electrocatalytic durability, retaining respective 28.1-and 19.2-fold enhancements in Pd-MSA compared to the commercial Pd/C, after 1 h chronoamperometric and 500-cycle potential cycling degradation tests. This study not only provides an effective and versatile synthetic strategy to prepare the NM-efficient metal-based nanomaterials with the special CG and SD structures for various electrocatalytic and energy-conversion applications, but also proposes some insights into the composition-and structure-function relations in EOR electrocatalytic mechanism for rationally designing highly active and durable EOR electrocatalysts.

The selective oxidation of propylene with O2 to propylene oxide and acrolein is of great interest and importance. We report the crystal-plane-controlled selectivity of uniform capping-ligand-free Cu2 O octahedra, cubes, and rhombic dodecahedra in catalyzing propylene oxidation with O2 : Cu2 O octahedra exposing {111} crystal planes are most selective for acrolein; Cu2 O cubes exposing {100} crystal planes are most selective for CO2 ; Cu2 O rhombic dodecahedra exposing {110} crystal planes are most selective for propylene oxide. One-coordinated Cu on Cu2 O(111), three-coordinated O on Cu2 O(110), and two-coordinated O on Cu2 O(100) were identified as the catalytically active sites for the production of acrolein, propylene oxide, and CO2 , respectively. These results reveal that crystal-plane engineering of oxide catalysts could be a useful strategy for developing selective catalysts and for gaining fundamental understanding of complex heterogeneous catalytic reactions at the molecular level.

Identification of the active site is important in developing rational design strategies for solid catalysts but is seriously blocked by their structural complexity. Here, we use uniform Cu nanocrystals synthesized by a morphology-preserved reduction of corresponding uniform Cu2O nanocrystals in order to identify the most active Cu facet for low-temperature water gas shift (WGS) reaction. Cu cubes enclosed with {100} facets are very active in catalyzing the WGS reaction up to 548 K while Cu octahedra enclosed with {111} facets are inactive. The Cu–Cu suboxide (CuxO, x ≥ 10) interface of Cu(100) surface is the active site on which all elementary surface reactions within the catalytic cycle proceed smoothly. However, the formate intermediate was found stable at the Cu–CuxO interface of Cu(111) surface with consequent accumulation and poisoning of the surface at low temperatures. Thereafter, Cu cubes-supported ZnO catalysts are successfully developed with extremely high activity in low-temperature WGS reaction.

Via a comprehensive time-resolved Operando-DRIFTS study of the evolutions of various surface species on Au/CeO 2 catalysts with Au particle sizes ranging from 1.7±0.6 to 3.7±0.9 nm during CO oxidation at room temperature, we have successfully demonstrated size-dependent reaction pathways and their contributions to the catalytic activity. The types and concentrations of chemisorbed CO(a), carbonate, bicarbonate and formate species formed upon CO adsorption,their intrinsic oxidation/decomposition reactivity and roles in CO oxidation vary with the size of supported Au particles. The intrinsic oxidation reactivity of CO(a) does not depend much on the Au particle size whereas the intrinsic decomposition reactivity of carbonate, bicarbonate and formate species strongly depend on the Au particle size and are facilitated over Au/CeO 2 catalysts with large Au particles. These results greatly advances the fundamental understanding of the size effect of Au/CeO 2 catalysts for low-temperature CO oxidation.

A gas-phase reaction network involving reactive intermediates such as alkyl and alkyl peroxide radicals and alkyl hydroperoxides have long remained a mystery in oxidative coupling of methane (OCM) and oxidative dehydrogenation of ethane (ODHE) reactions. Herein we report direct observations of gas-phase reactive intermediates including CH2, CH3•, C2H5•, CH3OO•, C2H5OO•, CH3OOH, and C2H5OOH during OCM and ODHE reactions over Li/MgO catalysts with an online synchrotron VUV photoionization mass spectrometer connected to a catalytic reactor with adjustable distances between the catalyst bed and the sampling nozzle of the mass spectrometer. Secondary reactions of these reactive intermediates in the gas phase are elucidated, and the reaction network of OCM and ODHE reactions is established. These results greatly deepen the mechanistic understanding of OCM and ODHE reactions necessary for developing efficient catalysts and designing proper reactors.

The PdO/Ce1–x Pd x O2−δ catalyst prepared by a solution-combustion method contained free surface PdO species and PdO species in Ce1–x Pd x O2−δ solid solution, whereas the PdO/CeO2 catalyst prepared by an impregnation method contained only free surface PdO species. The free surface PdO species could be removed by nitric acid. Contributions of the PdO species to catalytic CO oxidation were quantitatively evaluated. The free surface PdO species in the PdO/Ce1–x Pd x O2−δ catalyst had the highest activity (969.3 μmolCO gPd –1 s–1), those in the PdO/CeO2 catalyst had medium activity (109.0 μmolCO gPd –1 s–1), and the PdO species in the Ce1–x Pd x O2−δ solid solution had the lowest activity (13.2 μmolCO gPd –1 s–1). Synergetic effects of PdO species were responsible for the enhanced reactivity of the PdO/Ce1–x Pd x O2−δ catalyst, as the free surface PdO species provided CO chemisorption sites and the Ce1–x Pd x O2−δ solid solution generated more oxygen vacancies for oxygen activation.

Gas-phase methyl radicals have been long proposed as the key intermediate in catalytic oxidative coupling of methane, but the direct experimental evidence still lacks. Here, employing synchrotron VUV photoionization mass spectroscopy, we have directly observed the formation of gas-phase methyl radicals during oxidative coupling of methane catalyzed by Li/MgO catalysts. The concentration of gas-phase methyl radicals correlates well with the yield of ethylene and ethane products. These results lead to an enhanced fundamental understanding of oxidative coupling of methane that will facilitate the exploration of new catalysts with improved performance.

Summary Green synthesis of ammonia by electrochemical nitrogen reduction reaction (NRR) shows great potential as an alternative to the Haber-Bosch process but is hampered by sluggish production rate and low Faradaic efficiency. Recently, lithium-mediated electrochemical NRR has received renewed attention due to its reproducibility. However, further improvement of the system is restricted by limited recognition of its mechanism. Herein, we demonstrate that lithium-mediated NRR began with electrochemical deposition of lithium, followed by two chemical processes of dinitrogen splitting and protonation to ammonia. Furthermore, we quantified the extent to which the freshly deposited active lithium lost its activity toward NRR due to a parasitic reaction between lithium and electrolyte. A high ammonia yield of 0.410 ± 0.038 μg s −1 cm −2 geo and Faradaic efficiency of 39.5 ± 1.7% were achieved at 20 mA cm −2 geo and 10 mA cm −2 geo, respectively, which can be attributed to fresher lithium obtained at high current density.