The development of heterogeneous frustrated-Lewis-pair (FLP) catalysts from homogeneous FLP conception is of great promise in practical applications. While our recent discovery has shown that all-solid FLPs can be created on ceria via surface oxygen vacancy regulation ( Zhang Zhang Nat. Commun.2017815266), a sound understanding of the intrinsic property and reactivity of the solid FLPs is still expected. Here we present a comprehensive theoretical study on the FLPs (Ce···O) constructed on CeO2(110) and (100) surfaces by using density functional theory calculations. We find that the creation of surface oxygen vacancy can enhance both the acidity of FLP-acid site and the basicity of FLP-base site. The enhanced acidity and basicity of Lewis sites together with the elongated distance of Lewis pairs (Ce···O) contribute to the high activity of solid FLPs. The dissociative activation of H2 on FLPs experiences a heterolytic pathway (H2 → Hδ+ + Hδ−) with a low activation energy of 0.07 eV on CeO2(110) and 0.08 eV on CeO2(100). Unlike the phenomenon on stoichiometric CeO2 surfaces that the dissociated hydride (Hδ−) adsorbed at Ce sites is prone to transfer to more stable O sites, the hydride on FLPs can be stabilized at Ce sites and thus benefits the hydrogenation of acetylene via an easier pathway. The rate-determining barriers of acetylene hydrogenation on FLP-CeO2(110) and FLP-CeO2(100) are calculated to be 0.58 and 0.88 eV, respectively. These results could help to understand the nature of solid FLPs and pave the way for rational design of heterogeneous FLP catalysts.

The local coordination structure of metal sites essentially determines the performance of supported metal catalysts. Using a surface defect enrichment strategy, we successfully fabricated Pt atomic single-layer (Pt ASL ) structures with 100% metal dispersion and precisely controlled local coordination environment (embedded vs adsorbed) derived from Pt single-atoms (Pt 1 ) on ceria-alumina supports. The local coordination environment of Pt 1 not only governs its catalytic activity but also determines the Pt 1 structure evolution upon reduction activation. For CO oxidation, the highest turnover frequency can be achieved on the embedded Pt ASL in the CeO 2 lattice, which is 3.5 times of that on the adsorbed Pt ASL on the CeO 2 surface and 10−70 times of that on Pt 1 . The favorable CO adsorption on embedded Pt ASL and improved activation/reactivity of lattice oxygen within CeO 2 effectively facilitate the CO oxidation. This work provides new insights for the precise control of the local coordination structure of active metal sites for achieving 100% atomic utilization efficiency and optimal intrinsic catalytic activity for targeted reactions simultaneously.

No abstract

We present a three-dimensional imaging method using a pulsed laser as a flood illuminating source and an intensified camera as the receiver with exponentially modulated gain. The depth map of a scene is obtained from two intensity images and the depth accuracy is independent of the depth of the target in the scene. We demonstrate a depth-independent depth accuracy of 0.32 m in an indoor experiment and obtain a depth map of an outdoor scene ranging from 150 to 180 m under a lower signal to noise ratio condition.

No abstract

Probing and understanding the local chemical environment of an active site is essential for designing high-performance single-atom catalysts (SACs). Density functional theory (DFT) calculations were performed to investigate the ligand configuration and site geometry of MgAl2O4-supported iridium single atoms (Ir1) toward catalytic carbon monoxide (CO) oxidation. We employed MgAl2O4(111) and MgAl2O4(211) as the model substrates with adsorbed Ir single atoms of different site geometries. DFT calculations revealed that the Mg-site on MgAl2O4(111) and the step site on MgAl2O4(211) are the most stable adsorption sites for Ir single atoms. Irrespective of site choices, CO oxidation on supported Ir single atoms follows the Eley–Rideal (E–R) mechanism, in which the surface oxygen vacancies close to the Ir single atoms activate molecular O2 with a negligible barrier and the rate-limiting step is the gas-phase CO directly attacking the O–Ir species that is modulated by a CO ligand. First-principles X-ray absorption near-edge spectra of reaction intermediates along with in situ/operando X-ray absorption spectroscopy (XAS) suggest that Ir single atoms adsorb primarily on the step sites of MgAl2O4. However, microkinetic modeling predicts that a higher activity can be attained on the equally stable Mg-site, maximizing the population of which in catalyst synthesis might prove fruitful in future studies. Electronic structure analysis indicates that the CO ligand increases the reactivity of adsorbed oxygen atoms bound to Ir single atoms by increasing the antibonding nature of the O–Ir bond.

No abstract

An alias-robust least squares method that produces less errors than established methods is developed to produce reference radial velocities for automatically correcting raw aliased Doppler velocities scanned from hurricanes. This method estimates the maximum tangential velocity V M and its radial distance R M from the hurricane vortex center by fitting a parametric vortex model directly to raw aliased velocities at and around each selected vertical level. In this method, aliasing-caused zigzag discontinuities in the relationship between the observed and true radial velocities are formulated into the cost function by applying an alias operator to the entire analysis-minus-observation term to ensure the cost function to be smooth and concave around the global minimum. Simulated radar velocity observations are used to examine the cost function geometry around the global minimum in the space of control parameters (V M , R M ). The results show that the global minimum point can estimate the true (V M , R M ) approximately if the hurricane vortex center location is approximately known and the hurricane core and vicinity areas are adequately covered by the radar scans, and the global minimum can be found accurately by an efficient descent algorithm as long as the initial guess is in the concave vicinity of the global minimum. The method is used with elaborated refinements for automated dealiasing, and this utility is highlighted by an example applied to severely aliased radial velocities scanned from a hurricane.