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WIREs Comput Mol Sci
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Toward computational design of chemical reactions with reaction phase diagram

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Abstract Density functional theory (DFT) was rapidly developed and achieved a great success in the last decades. As the advancement of general concepts in heterogeneous catalysis, theoretical study of chemical reactions based on DFT calculations has become more and more feasible, which provides a guideline for the rational design of novel catalysts toward higher reaction activity and specific selectivity. Here, we review an innovate scheme, namely reaction phase diagram (RPD), which can offer not only an in‐depth understanding of reaction mechanisms, but also the prediction of catalytic activity and selectivity trend over a collection of catalysts. The RPD analysis was successfully applied to understand the activity variation of CO2 electroreduction to CO and formic acid, as well as thermochemical hydrogenation and dehydrogenation. Meanwhile, the RPD analysis also exhibits a success of studying the product selectivity in syngas conversion to methane, ethanol, and methanol with complicated reaction pathways. At the end, we review a successful case of catalyst rational design with a target of NO selective electroreduction to ammonia. The foundation of RPD analysis is based on the scaling relation of adsorption energies and the correlation between kinetic barriers and reaction energies at elementary steps. Therefore, microkinetic modeling is complementary to the RPD analysis. A few of limitations and the prospect of the development regarding the RPD analysis are addressed in this review. This article is categorized under: Structure and Mechanism > Reaction Mechanisms and Catalysis
Illustration of traditional strategy (black arrow) and innovate reaction phase diagram (red arrow). (a) The linear correlation, namely scaling relations, between adsorption energies of different adsorbates on a set of catalysts. (b) The linear correlation between activation barriers and adsorption energies for all possible elementary steps. (c) Activity (reaction rate) volcano curve, obtained by microkinetic modeling. (d) Rational design based on theoretical reaction rate. (e) Complete reaction pathway construction. (f) ΔG‐limiting steps and the limiting energies (dashed lines) obtained based on the reaction phase diagram. (g) Kinetic barriers for key steps (solid lines), indicating GRPD‐energies. (h) Rational design based on theoretical GRPD
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(a) Comparisons of the GRPD‐limiting steps between NORR, NRR, and HER. (b) A two‐dimensional activity map for ammonia production based on NORR. The adsorption energies of N* and NOH* are applied to be two independent descriptors. (c) Free energy diagrams for HER and NORR producing NH3, N2O, and N2 at 0 V versus RHE. Numbers show the activation barriers in eV. (d) Geometries of the IS, TS, and FS for NOH* + (H+ + e) → N* + H2O and (e) N* + (H++e) → NH*; the light red, red, blue, and white atoms refer to Cu, O, N, and H, respectively; the green atoms represent the hydrogen participating in the proton transfer. (f) Projected density of states (PDOS) and electron localization function (ELF) analysis for the transition state of NO + (H++e) → NOH*. (g) The experimental ammonia production rates over cu foam plotted as theoretical TOF based on microkinetic modeling at different potentials. Figure reprinted from ref. 3, copyright 2020 Wiley‐VCH Verlag GmbH & Co. KGaA
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The prediction of activity trend for electrocatalytic ORR with the scheme of reaction phase diagram (RPD) at 0.2 (a) and 0.7 (b) V versus RHE. The red and blue solid lines show the GRPD‐limiting steps based on electrochemical or thermochemical steps. (c) A comparison of the theoretically activity trend at 0.2 V versus RHE (insert figure for activity trend at 0.7 V vs. RHE) with the experimental activity trend. Potential dependent one‐dimension RPDs at 0.5 (d) and 0.9 (g) V versus RHE. Two‐dimension RPDs with the descriptor of O* and OH* adsorption energies at 0.5 (e) and 0.9 (h) V versus RHE. GRPD‐limiting steps for two‐dimension RPDs at 0.5 (f) and 0.9 (i) V versus RHE. Figure reprinted from ref. 64, copyright 2020 American Chemical Society
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(a) Two‐dimensional reaction phase diagram displaying theoretical selectivity producing CH4, CH3OH and CH3CH2OH. A 0.1 eV error bar is applied considering the system error from DFT calculations. The color refers to the GRPD‐limiting energy for protential determining steps (ΔGPDS). (b) The projected density of states Rh atoms in Rh‐rich (red line) site and interfacial site (black line). The calculated d‐band centers of two kinds of Rh atoms are indicated by red and black arrows. The insert structures show the configuration of Rh‐rich site and interfacial site. (c) The most feasible pathway along syngas conversion into ethanol with configurations of some important intermediates. Figure reprinted from ref. 63, copyright 2019 Elsevier Inc
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(a) Reaction phase diagram with the reaction free energy changes of involved elementary reactions, plotted versus Gad(*HCOO). A‐p, B‐p, C‐p shows different active sites on hydrocerussite perfect surface and A‐d, B‐d, C‐d refer to the active sites on defect surface. (b) Two‐dimensional reaction phase diagram displaying an activity and selectivity map for CO2RR producing formate. A second descriptor of COOH* adsorption energies were applied with an independent consideration. The black lines separate the areas with different favored products. The color shows a negative value of GRPD. (c) Potential dependent free energy diagram for CO2RR producing formate. (d) Comparisons between calculated rate of charge transfer (k, 10−17 C∙s−1∙site−1) and experimental current density (jexp). Figure reprinted from ref. 49, copyright 2020 Springer Nature Limited
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(a) The two‐dimension reaction phase diagrams for the EDH reaction on transition metal surfaces, based on two independent descriptors of Gad(H*) and Gad(CH2CH2*). (b) The separated areas with different limiting steps on metal surfaces. (c) Predicted activity on isolated metal sites of metal‐S‐1 catalysts. The descriptor Gad(CH2CH2*‐a) represents the interactions between ethene and the two Bronsted acids on the metal sites. (d) GRPD‐limiting steps for the EDH reaction over isolated metal sites of metal‐S‐1 catalysts. Rn (n = 1–4) is an abbreviation for R4‐3‐n. (e) Activation barriers for key elementary steps. (f) Comparisons between theoretically calculated selectivity based on microkinetic models over all studied catalysts with experimental yields of CH2CH2. Figure reprinted from ref. 34, copyright 2020 American Chemical Society
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(a) Flow chart of complete pathway construction. (b) The complicated reaction network considering all possible pathways. (c) Optimal pathway (red line) with global energy optimization, compared with other pathways (black dashed line). (d) The optimal pathway determined by GRPD‐limiting energy
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(a) The change of reaction energies (Er) (black line), barrier (blue line), and desorption free energy (red line) of elementary steps with respect to the descriptor of Ead(CH3). Triangle and circle points refer to the calculated energies on Pt(111) and [email protected], respectively. R4‐2‐4′ displays the reaction of further hydrogenation based on C8H8*. (b) Free energy diagram of phenylacetylene hydrogenation on Pt(111) (red line) and [email protected] (black line) with insert structures. Figure reprinted from ref. 54, copyright 2019 Elsevier
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(a) Reaction phase diagram with thermodynamic trend for CO2 reduction reaction. The black lines indicate the GRPD‐limiting steps of CO* desorption and CO2 protonation (determined by metal surfaces), respectively. The red circles with the fitted black dashed line represent the specific reaction free energy of CO2 protonation on different surfaces in the work. The blue lines show the changing of adsorption energies of CO* and H*. (b) Free energy diagram for CO2 reduction reaction on different Ag surfaces. (c) Optimized structures in CO2 reduction reaction on Ag(111) and Ag(111) with subsurface O. Figure reprinted from ref. 51, copyright 2020 Elsevier B.V
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Scaling relations for adsorption energies of (a) CH2OH*, (c) H* and (e) CH3* on transition metals, and (b) CH3OH*, (d) H*, and (f) CH3* on zeolites, plotted against the descriptor of Ead(CH2*). Adsorption energies on metal surfaces of Ni(211), Pd(211), Cu(211), Ag(211), and zeolites (DNL‐6, MOR12, MOR8, MOR12&8, ZSM‐5straight, SAPO‐18, SSZ‐13, ZSM‐5sinusoidal, SAPO‐34, ZSM‐22, and RUB‐50) were applied in the establishment of scaling relations. Adsorption energies were calculated either with (red points) or without (blue points) van der Waals correction. All the adsorption energies were calculated reference to the gas molecule energies of CH3OH, H2, and H2O. The data was adopted from ref. 47, copyright 2020 Royal Society of Chemistry
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