An accurate assessment of the effect of long-term rice cultivation on K-supplying capacity and adsorption characteristics of paddy soils has theoretical and practical significance for rational ...application of K fertilizers. We measured changes in basic soil properties and K adsorption isotherms in a representative subtropical paddy soil chronosequence in Southern China. Results showed that mean water dissolvable K and non-exchangeable K contents of paddy soils (27.0 and 184.8 mg kg
−1
) were higher than those of original soils (15.5 and 169.5 mg kg
−1
), but the mean exchangeable K contents showed the opposite trend (paddy soils, 37.1 mg kg
−1
; original soils, 52.5 mg kg
−1
). Long-term paddy cultivation caused reduced K-supplying capacity and K
+
adsorption capacity of paddy soils in the red soil regions, which was attributed to the rapid loss of sorbents (e.g. Fe
d
and clay) by leaching and the competitive occupation of sorption sites by the accumulated soil organic matter. The promotion of sustainable and balanced K fertilizer inputs and appropriate increase in short-term applications of K fertilizer (K fertilizer input > K output from harvest) during application of N and P fertilizers to paddy soils were necessary to maintain the K-supplying capacity of soils and the crop yield.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
Microkinetic model is developed in the free energy landscape based on density functional theory (DFT) to quantitatively investigate the reaction mechanism of chemoselective partial hydrogenation of ...crotonaldehyde to crotyl alcohol over Pt(1
1
1) at the temperature of 353
K. Three different methods (mobile, immobile and collision theory models) were carried out to obtain free energy barrier of adsorption/desorption processes. The results from mobile and collision theory models are similar. The calculated TOFs from both models are close to the experiment value. However, for the immobile model, in which the free energy barrier of desorption approaches the energy barrier, the calculated TOF is 2 orders of magnitude lower than the other models. The difficulty of adsorption/desorption may be overestimated in the immobile model. In addition, detailed analyses show that for the surface hydrogenation elementary steps, the entropy and internal energy effects are small under the reaction condition, while the zero-point-energy (ZPE) correction is significant, especially for the multi-step hydrogenation reaction. The total energy with the ZPE correction approaches to the full free energy calculation for the surface reaction under the reaction condition.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This study employs density functional theory (DFT) calculations to examine the mechanism by which acetaldehyde is formed on platinum in a typical direct ethanol fuel cell (DEFC). A pathway is found ...involving the formation of a strongly hydrogen-bonded complex between adsorbed ethanol and the surface hydroxyl (OH) species, followed by the facile α-dehydrogenation of ethanol, with spontaneous weakening of the hydrogen bond in favor of adsorbed acetaldehyde and water. This mechanism is found to be comparably viable on both the close-packed surface and the monatomic steps. Comparison of further reactions on these two sites strongly indicates that the steps act as net removers of acetaldehyde from the product stream, while the flat surface acts as a net producer.
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IJS, KILJ, NUK, PNG, UL, UM
Selective hydrogenation of nitroarene compounds is applied in many fields such as agrochemicals, pharmaceuticals, and dyes. Pd-catalyzed hydrogenation of nitrobenzene (PhNO2) and nitrosobenzene ...(PhNO) could exhibit different selectivities. This was regarded as the evidence to challenge the Haber mechanism for PhNO2 hydrogenation in which PhNO is an important intermediate. In this study, we systematically investigate their hydrogenation mechanisms under realistic reaction conditions based on first-principles calculations. It is found that the weak bonding between the nitro group and the Pd(111) surface leads to the flat-lying chemisorption configuration of PhNO2 and the other intermediates during PhNO2 hydrogenation. In contrast, the strong bonding between the nitroso group and the surface makes PhNO switch its chemisorption mode from flat-lying adsorption under the ultrahigh vacuum condition to vertical adsorption under reaction conditions. For the flat-lying PhNO2, the chemisorbed phenyl group makes hydrogenation easier but hinders N–O bond breaking, resulting in the production of PhNH2 via a direct pathway. Conversely, without the hinderance of the chemisorbed phenyl group, N–O bond breaking and N–N coupling become more favorable during the reduction of vertical PhNO* toward the formation of azoxy compound on Pd(111). These results unveil the fact that the difference between the selectivities of PhNO2 and PhNO hydrogenation is independent of the formation of PhNO* but dependent on the phenyl group adsorption mode.
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IJS, KILJ, NUK, PNG, UL, UM
We have performed density functional theory (DFT) calculations to investigate the reaction mechanism of the cleavage of the carbonyl bond in amides on both flat and stepped Ru surfaces. The simplest ...amide molecule, N,N-dimethylacetamide (DMA), was used as the exemplar model molecule. Through the calculations, the most stable transition states (TSs) in all the pathways on both flat and stepped Ru surfaces are identified. Comparing the energy profiles of different reaction pathways, we find that a direct cleavage mechanism is always energetically favored as compared with an alternative hydrogen-induced mechanism on either the flat or stepped Ru surface. It is easier for the dissociation process to occur on the stepped surface than on the flat surface. However, as compared with the terrace, the superiority of step sites boosting the C–O bond dissociation is not as evident as that on CO dissociation.
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IJS, KILJ, NUK, PNG, UL, UM
The efficiency of direct catalytic oxidation of methane to methanol (DMTM) is significantly influenced by oxidants. However, realizing a one-pot DMTM using dioxygen remains challenging. Hydrogen ...peroxide is still the most frequently reported green oxidant for DMTM, with high selectivity for methanol. To gain insight into the influence of oxidants on DMTM performance, we computationally investigated the reaction mechanisms involved in DMTM using H2O2 at mono-copper sites in three types of Cu-exchanged zeolites with different micropore sizes. We identified the advantages and limitations of H2O2 as an oxidant. In contrast to the O–O bond in O2, the O–O bond in H2O2 can be easily broken to produce reactive surface oxygen species, which enable the facile C–H bond activation of methane at a low temperature. However, because of the radical-like process of C–H bond activation at mono-copper sites, actualizing the preferential C–H bond activation of methane is kinetically challenging compared to that of methanol. Moreover, the lower O–H bonding energy of H2O2 would result in self-decomposition of H2O2. Despite these bottlenecks, kinetic analysis shows that improving catalysts to boost the DMTM performance using H2O2 is a promising approach.
Compared with O2, the O–O bond of H2O2 is easily broken to generate surface reactive hydroxyl to activate methane. However, the weaker C–H bond of CH3OH and O–H bond of H2O2 leads to the trade-off between CH4 conversion and CH3OH selectivity and the preferential self-decomposition of hydrogen peroxide.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Comparing the chemical bonding strengths between different functional groups of nitroarenes and metal surfaces.•Obtaining the variation trends of adsorption configurations of ...nitrobenzene and 4-nitrostyrene against their coverage.•Identifying the coverage of nitroarene and hydrogen on Pt(111) and Au(111) under the realistic hydrogenation condition.•Proposing Gibbs free adsorption energy per surface area as a descriptor to roughly evaluate the hydrogenation selectivity.
The adsorption of nitrobenzene and 4-nitrostyrene on the Pt(111) and the Au(111) surfaces under the general reaction condition of nitroarene catalytic hydrogenation is investigated utilizing periodic density functional theory calculations with the Grimme’s empirical three-body dispersion correction to understand the influence of adsorption configurations on chemoselectivity of nitroarene compound hydrogenation. It is found that at the low coverage both nitrobenzene and 4-nitrostyrene tend to adsorb paralleling to the Pt(111) and the Au(111) surfaces. Based on the crystal orbital Hamilton population analysis, it is found that the chemical bonding between nitro group and Pt(111) surface is weak. The adsorption configurations of nitrobenzene and 4-nitrostyrene are determined by the chemisorption strength of phenyl group and vinyl group. Under the reaction condition, the 1/9 ML nitrobenzene and 4/9 ML hydrogen atom can be coadsorbed while the 1/6 ML 4-nitrostyrene and 1/3 ML hydrogen atom can be coadsorbed on Pt(111). With the increase of the coverage, nitrobenzene still remains its paralleled adsorption configuration while the adsorption configuration of 4-nitrostyrene is switched to the tilted adsorption configuration through vinyl group without the chemisorption of phenyl and nitro group on Pt(111). In addition, the competitive adsorption with hydrogen will not change the adsorption configuration of nitrobenzene and 4-nitrostyrene under the reaction condition. On Au(111), the physical adsorption strength determines the adsorption configuration. The paralleled adsorption with the shortest average distance between the adsorbate and Au(111) surface is preferred. At the paralleled adsorption configuration, the chemoselectivities of the hydrogenation on these functional groups are similar if only in terms of geometric configuration. However, the hydrogenation on nitro group encounters the problem of steric hindrance at the tilted adsorption configuration through vinyl group, which makes it unfavorable. Therefore, the catalysts which could form strong chemical bonding with nitro group, leading to the preferential vertical adsorption configuration via nitro group, are expected for the high selectivity towards nitro group hydrogenation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Single-atom catalysts have been applied in many processes recently. The difference of their kinetic behavior compared to the traditional heterogeneous catalysts has not been extensively discussed ...yet. Herein a complete catalytic cycle of CH4 combustion assuming to be confined at isolated single sites of the Co3O4(110) surface is computationally compared with that on multi sites. The macroscopic kinetic behaviors of CH4 combustion on Co3O4(110) is systematically and quantitatively compared between those on the single site and multi sites utilizing kinetic Monte Carlo simulations upon the energetic information from the PBE + U calculation and statistic mechanics. The key factors governing the kinetics of CH4 combustion are disclosed for both the catalytic cycles respectively following the single-site and multi-site mechanisms. It is found that cooperation of multi active sites can promote the activity of complete CH4 combustions substantially in comparison to separated single-site catalyst whereas the confinement of active sites could regulate the selectivity of CH4 oxidation. The quantitative understanding of catalytic mechanism paves the way to improve the activity and selectivity for CH4 oxidation.
Systematical first-principles kinetic Monte Carlo simulations of CH4 combustion on Co3O4(110) show that the cooperation of multi active sites can promote the activity of complete CH4 combustions substantially in comparison to separated single-site catalyst whereas the confinement of active sites could regulate the selectivity of CH4 oxidation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Based on the land cover datasets of Poyang Lake region in 1980, 2005, and 2010, and by using GIS, RS, and landscape ecology approaches, this paper studied the land cover and landscape pattern changes ...in this region from 1980 to 2010, and quantitatively analyzed the land cover types change degree, patch area index, patch shape index, margin density index, and landscape diversity index. In 1980-2010, the main land cover types in this region were paddy field, inland water, evergreen broadleaf forest, and urban built-up area, and their areas and spatial patterns varied dramatically. Overall, the areas of inland water and urban built-up area had a significant increase, while those of paddy field and dry farmland decreased somewhat. Due to the effects of population growth and economic development, the landscape fragmentation degree and landscape diversity index presented a decreasing trend, but the decrement was small, which implied that the previous environmental management of this region had exerted important rol
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