Acetate coverage effect on the reactivity of vinyl acetate synthesis on Pd/Au alloy surfaces

Vinyl acetate （VA） synthesis on Pd/Au（111） and Pd/Au（100） surfaces has been systematically investigated through first-principles density functional theory （DFT） calculations. The DFr results showed that for VA synthesis, the ＇Samanos＇ reaction mechanism （i.e., direct coupling of coadsorbed ethylene and acetate species and subsequent/%hydride elimination to form VA） is more favorable than the ＇Moiseev＇ mechanism （i.e., ethylene first dehydrogenates to form vinyl species which then couple with the coadsorbed acetate species to form VA）. More importantly, it was found the surface coverage of acetate has a significant effect on the reactivity of VA synthesis, and the activation energy of the rate- controlling step on Pd/Au（100） surface is smaller than that on Pd/Au（111） surface （0.88 vs. 0.95 eV）, indicating the former is more active than the latter.

Models to Simulate Effective Coverage of Fire Station Based on Real-Time Travel Times

In recent years,frequent fire disasters have led to enormous damage in China.Effective firefighting rescues can minimize the losses caused by fires.During the rescue processes,the travel time of fire trucks can be severely affected by traffic conditions,changing the effective coverage of fire stations.However,it is still challenging to determine the effective coverage of fire stations considering dynamic traffic conditions.This paper addresses this issue by combining the traveling time calculationmodelwith the effective coverage simulationmodel.In addition,it proposes a new index of total effective coverage area(TECA)based on the time-weighted average of the effective coverage area(ECA)to evaluate the urban fire services.It also selects China as the case study to validate the feasibility of the models,a fire station(FS-JX)in Changsha.FS-JX station and its surrounding 9,117 fire risk points are selected as the fire service supply and demand points,respectively.A total of 196 simulation scenarios throughout a consecutiveweek are analyzed.Eventually,1,933,815 sets of valid sample data are obtained.The results showed that the TECA of FS-JX is 3.27 km^(2),which is far below the standard requirement of 7.00 km^(2) due to the traffic conditions.The visualization results showed that three rivers around FS-JX interrupt the continuity of its effective coverage.The proposed method can provide data support to optimize the locations of fire stations by accurately and dynamically determining the effective coverage of fire stations.

Reveal the nature of particle size effect for CO_(2) reduction over Pd and Au

Small cluster and periodic surface models with low coverages of intermediates are frequently employed to investigate reaction mechanisms and identify active sites on nanoparticles(NPs)in density functional theory(DFT)studies.However,diverse active sites on NPs cannot be sufficiently represented by these simple models,hampering the in-depth insights into the catalytic behavior of NPs.This paper describes the crucial roles of both model and coverage effect on understanding the nature of active sites for CO_(2)reduction over Au and Pd NPs using DFT calculations.Terrace sites exhibit higher selectivity for CO than edge sites on Au NPs,which is opposite to the results on Au periodic surfaces.This contradiction reveals the computational model effect on clarifying active site properties.For Pd catalysts,the coverage effect is more significant.On bare Pd NPs and periodic surfaces,the selectivity for CO at edge sites is nearly identical to that at terrace sites,whereas edge sites display higher selectivity for CO than terrace sites in the case of high CO coverages.Through considering the more realistic models and the coverage effect,we successfully describe the size effect of Au and Pd NPs on CO selectivity.More importantly,this work reminds us of the necessity of reasonable models in DFT calculations.

Multi-agent coverage control design with dynamic sensing regions

A cooperative region reconnaissance problem is considered in this paper where a group of agents are required to reconnoitre a region of interest. Amain challenge of this problem is the sensing region of each agent varies with its altitude within an altitude constraint. Meanwhile, the reconnaissance ability of an agent is determined by its altitude and radial distance. First, the region reconnaissance is formulated as an effective coverage problem, which means that each point in the given region should be surveyed until a preset level is achieved. Then, an effective coverage control law is proposed to minimize coverage performance index by adjusting the altitude of an agent. Finally, the effectiveness of the proposed control law is verified through numerical simulations.

Density Functional Theoretical Studies on the Methanol Adsorption and Decomposition on Ru（0001） Surfaces

Periodic density functional theory（DFT） calculations are presented to describe the adsorption and decomposition of CH3OH on Ru（0001） surfaces with different coverages, including p（3 ×2）, p（2×2）, and p（2× 1） unit cells, corresponding to monolayer（ML） coverages of 1/6, 1/4, and 1/2, respectively. The geometries and energies of all species involved in methanol dissociation were analyzed, and the initial decomposition reactions of methanol and the subsequent dehydrogenations reactions of CH3O and CH2OH were all computed at 1/2, 1/4, and 1/6 ML coverage on the Ru（0001） surface. The results show that coverage exerts some effects on the stable adsorption of CH30, CH2OH, and CH3, that is, the lower the coverage, the stronger the adsorption. Coverage also exerts effects on the initial decomposition of methanol. C-H bond breakage is favored at 1/2 ML, whereas C-H and O--H bond cleavages are preferred at 1/4 and 1/6 ML on the Ru（0001） surface, respectively. At 1/4 ML coverage on the Ru（0001） surface, the overall reaction mechanism can be written as 9CH3OH ,3CH30＋6CH2OH＋9H ,6CH20＋3CHOH＋18H , 7CHO＋COH＋CH＋OH＋26H → 8CO＋C＋O＋36H.