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• S or Si modified Pd-based catalysts can well tune the spatial scale of Pd active site. • Catalytic performance of C 2 H 2 semi-hydrogenation can be tuned by changing Pd active sites spatial scale. • The electronic effect induced by S atoms is stronger than that by Si atoms. • The geometrical effect induced by Si atoms is stronger than that by S atoms. • Sever types of Pd-based catalysts modified by S or Si atoms exhibit better catalytic performance. Modifying the spatial scale of active site has been proven a good strategy for enhancing catalytic performance. In this study, the Pd-based catalysts with different spatial scale of active site were constructed via the modification of non-metallic S or Si atoms over Pd, Cu alloyed Pd SACs, PdAg surface alloy and PdM (M =Au, Ag) IMCs catalysts, then, C 2 H 2 semi-hydrogenation catalytic performance was identified based on DFT calculations. The findings indicate that the catalytic performance of C 2 H 2 semi-hydrogenation is greatly influenced by the spatial extent of active site and the electronic effect modified by the S or Si atoms. Geometric effect caused by S or Si atoms reduces the spatial scale of active site over S/Pd-2 × 2, Si/Pd-3 × 3, S/Pd 6 Ag, S/Pd 1 Au 1 , S/Pd 1 Ag 1 and Si/Pd 1 Ag 1 , thereby preventing green oil generation. Electronic effect caused by S or Si atoms leads to far away from the Fermi level of d -band center over S/Pd-2 × 2, Si/Pd-3 × 3, S/Pd 1 Au 1 , S/Pd 1 Ag 1 and Si/Pd 1 Ag 1 to improve C 2 H 4 production activity and selectivity. Seven catalysts S/Pd-2 × 2, Si/Pd-3 × 3, PdCu-2 × 2, S/Pd 6 Ag, S/Pd 1 Au 1 , S/Pd 1 Ag 1 and Si/Pd 1 Ag 1 are screened out to present high selectivity and activity of C 2 H 4 production, and effectively prevent green oil generation. This study provides valuable structural insights for designing high-performance catalysts by the modification of non-metallic atom in C 2 H 2 semi-hydrogenation. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydrogenation on N -containing ring in quinoline to generate tetrahydroquinoline tends to be more favorable compared to the hydrogenation of benzene ring. • The catalyst's hydrogenation activity correlates positively with the displacement of the d -band center from the Fermi energy level. • A novel C− N bond cleavage mechanism different from E2 an S N 2 is proposed. • Pd ML /Mo 2 C(0 0 1) is an excellent catalyst for quinoline hydrogenation and C− N bond cleavage. Nitrogen-containing compounds such as quinoline in coal-based crude oils cause environmental pollution in the course of application. Consequently, dealing with the nitrogen-containing compounds from coal-based crude oil is of paramount importance. The hydrogenation and C N bond cleavage mechanisms of quinoline on the active Mo-terminated over Mo 2 C(0 0 1) surface, as well as on surfaces doped with W, Pt and Pd monolayers, were examined employing the density functional theory (DFT) method. The Pd and Pt-doped catalysts exhibited higher hydrogenation activity. The catalytic efficiency is enhanced by the loading of different metals, particularly with d -band center further away from the Fermi energy level. Additionally, a novel C N bond cleavage mechanism for quinoline has been proposed. The new proposed mechanism is more conducive for the C N bond cleavage. After a thorough comparison, the Pd-loaded catalyst was identified as the most effective for quinoline hydrogenation and C N bond cleavage. [ABSTRACT FROM AUTHOR]

Effects of surface‐adsorbed O and lattice O for the CeO2(111) surface on Hg removal has been researched. In this work, periodic calculations based on density functional theory (DFT) were performed with the on‐site Coulomb interaction. Hg is oxidized to HgO via the surface‐adsorbed O by overcoming a Gibbs free energy barrier of 114.1 kJ·mol−1 on the CeO2(111) surface. Mn and Fe doping reduce the activation Gibbs free energy for the Hg oxidation, and energies of 70.7 and 49.6 kJ·mol−1 are needed on Ce0.96Mn0.04O2(111) and Ce0.96Fe0.04O2(111) surfaces. Additionally, lattice O also plays an important role in Hg removal. Hg cannot be oxidized leading to the formation of HgO on the un‐doped CeO2(111) surface owing to the inertness of lattice O, which can be easily oxidized to HgO on Ce0.96Mn0.04O2(111) and Ce0.96Fe0.04O2(111) surfaces. It can be seen that both surface‐adsorbed O and lattice O play important roles in removing Hg. The present study will shed light on understanding and developing Hg removal technology on un‐doped and Mn/Fe‐doped CeO2(111) catalysts. © 2019 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: The catalytic activity and selectivity of cost‐effective noble‐metal‐doped common metal materials strongly depend on the doped atom ensemble in specific arrangements to provide active sites. In this study, aiming at insight into the doped atom ensembles as active sites for tuning the selectivity and activity towards the target reaction, different doped noble metal Pd atom ensembles for cost‐effective Pd‐doped Cu catalysts act as active sites to investigate the activity and selectivity towards the efficient removal of acetylene from ethylene by using density functional theory calculations. The results show that an ensemble composed of one surface and its joint sublayer Pd atoms in the Cu catalyst as active sites enhance both the selectivity and activity of C2H4 formation caused by adjusting the catalyst surface electronic structure. Moreover, the surface d‐band center of the Pd‐doped Cu catalyst can act as an effective “descriptor” for the rapid screening of catalytic activity in the design of improved catalysts with the noble‐metal‐doped common metal. Further, the ensemble composed of one surface and its joint sublayer doped Pd atoms as active sites in the cost‐effective Pd‐doped Cu bimetallic catalysts is an efficient approach to finely tune the activity and selectivity towards the efficient removal of acetylene from ethylene. [ABSTRACT FROM AUTHOR]

Understanding the formation mechanism of carbon nanotubes (CNTs) from carbon source is critical for controlled-production of CNTs. In this study, the functions of carbon species were investigated by a thermogravimetric analyzer coupled with a mass spectroscope in using methane as carbon source of CNT growth in chemical vapor deposition (CVD). It was found that a negative peak of C 2 H 2 species and a positive peak of C 2 H 4 species appeared at the CNT growth moment. Accordingly it is deduced that the C 2 H 2 species react on nucleation and C 2 H 4 species react on CNT growth. This deduction is then verified by the computational chemistry results based on density functional theory (DFT). This finding clarifies the different functions of C 2 at growing moment at the first time and makes the controlling of CNT production in such a condition becomes promising. [ABSTRACT FROM AUTHOR]

Highlights: [•] Propose a theoretical basis for catalyst design. [•] The activation energy of CH4 dissociation is predicted without C deposition. [•] Using adsorption energy to instead of the properties of catalyst surfaces. [ABSTRACT FROM AUTHOR]

Abstract: CH4 dehydrogenation on Rh(111), Rh(110) and Rh(100) surfaces has been investigated by using density functional theory (DFT) slab calculations. On the basis of energy analysis, the preferred adsorption sites of CH x (x =0–4) and H species on Rh(111), Rh(110) and Rh(100) surfaces are located, respectively. Then, the stable co-adsorption configurations of CH x (x =0–3) and H are obtained. Further, the kinetic results of CH4 dehydrogenation show that on Rh(111) and Rh(100) surfaces, CH is the most abundant species for CH4 dissociation; on Rh(110) surface, CH2 is the most abundant species, our results suggest that Rh catalyst can resist the carbon deposition in the CH4 dehydrogenation. Finally, results of thermodynamic and kinetic show that CH4 dehydrogenation on Rh(100) surface is the most preferable reaction pathway in comparison with that on Rh(111) and Rh(110) surfaces. [Copyright &y& Elsevier]

Abstract: Interactions of atomic and molecular hydrogen with perfect and deficient Cu2O(111) surfaces have been investigated by density functional theory. Different kinds of possible modes of H and H2 adsorbed on the Cu2O(111) surface and possible dissociation pathways were examined. The calculated results indicate that OSUF, CuCUS and Ovacancy sites are the adsorption active centers for H adsorbed on the Cu2O(111) surface, and for H2 adsorption over perfect surface, CuCUS site is the most advantageous position with the side-on type of H2. For H2 adsorption over deficient surface, two adsorption models of H2, H2 adsorbing perpendicularly over Ovacancy site and H2 lying flatly over singly-coordinate Cu–Cu short bridge, are typical of non-energy-barrier dissociative adsorption leading to one atomic H completely inserted into the crystal lattice and the other bounded to CuCUS atom, suggesting that the dissociative adsorption of H2 is the main dissociation pathway of H2 on the Cu2O(111) surface. Our calculation result is consistent with that of the experimental observation. Therefore, Cu2O(111) surface with oxygen vacancy exhibits a strong chemical reactivity towards the dissociation of H2. [ABSTRACT FROM AUTHOR]

• Pd-Ag surfaces without Pd atoms, with isolated Pd atom or Pd dimer exhibit poor C 2 H 4 selectivity. • Pd-Ag surfaces with the Pd trimer exhibit better C 2 H 4 selectivity. • Pd-doped Ag catalysts with surface Pd trimer are promising based on the cost and catalytic performance. • D-band center of Pd-Ag catalyst with better C 2 H 4 selectivity far from Fermi energy level improves catalytic activity. • More average charges of surface Pd atoms for Pd-Ag catalyst with better C 2 H 4 selectivity enhance catalytic activity. Aiming at identifying the effects of surface composition and ensemble effect for the Pd-Ag bimetallic catalysts on the catalytic performance of C 2 H 2 semi-hydrogenation, the selectivity and activity of C 2 H 4 formation over the Ag-doped Pd, Pd-doped Ag catalysts and PdAg intermetallic compounds with different surface composition and ensemble effect are examined utilizing density functional theory calculations. The results indicated that the Pd-Ag bimetallic catalysts without Pd atoms, with isolated Pd atom or Pd dimer on the surface show poor C 2 H 4 selectivity; while those with surface Pd trimer exhibit better C 2 H 4 selectivity, especially, the Pd-doped Ag catalysts present better catalytic performance and low cost. This study not only helps scientists understand reaction theories associated with the experiment of C 2 H 2 semi-hydrogenation over the Pd-Ag bimetallic catalysts, but also helps them advance the design of high-performance, cost-effective and structure-tunable Pd-Ag bimetallic catalysts for C 2 H 2 removal from C 2 H 4 , which has broad impact on catalyst development. [ABSTRACT FROM AUTHOR]

• The activity and selectivity of HCOOH dissociation depend on the core metal type of M@Pd. • The selectivity of CO 2 reach nearly 99.99% over the M@Pd(M = Au, Ag, Ni and Co) catalysts. • Ag@Pd catalyst exhibits the best activity toward HCOOH dissociation to form CO 2. • The Bader charge and d -band center of shell Pd identify the function of core metal. • Ligand effect caused by charge transfer between the core metal to shell Pd plays a key role. The core-shell bimetallic catalysts have exhibited unique catalytic performance due to the bimetallic synergetic effect. In this work, the catalytic activity and selectivity of HCOOH dissociation on the M core @Pd shell (M = Cu, Au, Co, Ni, Ag, Al) catalysts are investigated to reveal the effect of the core metal on the shell Pd catalytic performance. Density functional theory calculations with microkinetic modeling are used. The results showed that compared to the Pd catalyst, M@Pd(M = Au, Co, Ni, Ag) catalysts are highly selective to CO 2 formation, while Al@Pd is favorable for CO formation. Especially, Ag@Pd catalyst not only presents the best activity and selectivity toward CO 2 generation, but also decreases CO adsorption ability to inhibit its poisoning and reduce noble Pd usage. The analysis of the electronic properties about the average Bader charge and d -band center corresponding to the shell Pd identify the function of the core metal type in adjusting the shell Pd catalytic performance toward HCOOH dissociation, in which the ligand effect caused by charge transfer between the core metal to the shell Pd plays a key role. This study provides valuable information for the improved performance of the core-shell bimetallic catalysts by altering the types of core metal. [ABSTRACT FROM AUTHOR]

Systematic periodic density functional theory computations including dispersion correction (DFT-D) were carried out to determine the preferred location site of Zr atoms in sodalite (SOD) and CHA-type topology frameworks, including alumino-phosphate-34 (AlPO-34) and silico-alumino-phosphate-34 (SAPO-34), and to determine the relative stability and Brönsted acidity of Zr-substituted forms of SOD, AlPO-34, and SAPO-34. Mono and multiple Zr atom substitutions were considered. The Zr substitution causes obvious structural distortion because of the larger atomic radius of Zr than that of Si, however, Zr-substituted forms of zeolites are found to be more stable than pristine zeolites. Our results demonstrate that in the most stable configurations, the preferred favorable substitutions of Zr in substituted SOD have Zr located at the neighboring sites of the Al-substituted site. However, in the AlPO-34 and SAPO-34 frameworks, the Zr atoms are more easily distributed in a dispersed form, rather than being centralized. Brönsted acidity of substituted zeolites strongly depends on Zr content. For SOD, substitution of Zr atoms reduces Brönsted acidity. However, for Zr-substituted forms of AlPO-34 and SAPO-34, Brönsted acidity of the Zr-O(H)-Al acid sites are, at first, reduced and, then, the presence of Zr atoms substantially increased Brönsted acidity of the Zr-O(H)-Al acid site. The results in the SAPO-34-Zr indicate that more Zr atoms substantially increase Brönsted acidity of the Si-O(H)-Al acid site. It is suggested that substituted heteroatoms play an important role in regulating and controlling structural stability and Brönsted acidity of zeolites. [ABSTRACT FROM AUTHOR]

[Display omitted] • Shell structure of Pt 3 M@Pt and Pt@Pt 3 M can tune catalytic performance of ethane dehydrogenation. • kMC simulations obtain catalytic performance and coke formation under the realistic conditions. • The catalyst Pt 3 Ni@Pt is screened out to exhibit excellent performance of ethane dehydrogenation. • Pt 3 Ni@Pt is superior to previously reported Pt, Pt 3 Sn, 1Pt 3 Sn@4Pt, Pd 1 -NDG, Pt 2 /Al 2 O 3 and Rh/ZrO 2 catalysts. • H adsorption energy is proposed as a descriptor to quantitatively evaluate C 2 H 4 (g) formation activity. Ethane direct dehydrogenation (EDH) operated at high temperature easily leads to coke formation. The new core–shell catalysts with monolayer shell exhibited better catalytic performance, and the function of monolayer shell structure is of great importance. This work fully investigated catalytic performance of EDH over six types of core–shell Pt 3 M@Pt and Pt@Pt 3 M (M = Fe, Co, and Ni) catalysts with Pt 3 M and Pt monolayer shell under the experimental conditions. Here, density functional theory (DFT) calculations with kinetic Monte Carlo (kMC) simulations were employed. The results show that the metal M over Pt 3 M@Pt surface decreases coordination number of Pt-Pt and restricts deep dehydrogenation reactions. The Pt 3 M@Pt catalysts with d- band center close to Fermi level exhibit higher C 2 H 4 (g) formation activity than Pt@Pt 3 M catalysts at 873.15 K. H 2 (g) co-feeding significantly decreases the coverage of coking C*+CC* species. The screened Pt 3 Ni@Pt catalyst presents the highest C 2 H 4 (g) formation activity and 100 % selectivity at the H 2 (g) partial pressure of 0.1 bar and reaction temperature 873.15 K, which is superior to previously reported Pt, Pt 3 Sn, 1Pt 3 Sn@4Pt, Pd 1 -NDG, Pt 2 /Al 2 O 3 and Rh/ZrO 2 catalysts. H* adsorption energy is proposed as a descriptor to quickly evaluate C 2 H 4 (g) formation activity. This work provides a useful strategy for designing alkane dehydrogenation catalysts by tuning monolayer shell structure and coordination environment of active site. [ABSTRACT FROM AUTHOR]

Aiming at identifying the effects of Pd ensemble and cluster size on the selectivity and activity of C 2 H 2 selective hydrogenation over Pd-modified Cu nano-cluster catalysts, the catalytic performance of C 2 H 2 selective hydrogenation over different cluster sizes of Pd-modified Cu catalyst with different Pd ensemble are examined using density functional theory calculations. A new evaluation method of the C 2 H 4 selectivity is defined. The results indicate that the promoter Pd cannot improve C 2 H 4 selectivity and activity over the small-sized Cu 13 and the large-sized Cu 55 clusters. Only when Cu catalyst has a moderate size such as Cu 38 cluster, the Pd ensemble composed of outer shell with 6 coordination and its contiguous inner-layer Pd atoms can significantly improve C 2 H 4 selectivity and activity. This study provides a theoretical clue for the design of highly efficient and cost-effective noble promoter-modified Cu-based catalysts by controlling the cluster size and the promoter ensemble for C 2 H 2 selective hydrogenation. Unlabelled Image • Pd ensemble and cluster size of Pd-modified Cu catalyst affect the selectivity of C 2 H 2 hydrogenation. • A new evaluation method of the selectivity toward C 2 H 4 formation is proposed. • Promoter Pd can affect the catalytic performance of moderate-size Cu catalyst. • Pd ensemble is effective for improving the activity and selectivity of Cu catalyst. • The promoter Pd atom as active center should has more negative charges. [ABSTRACT FROM AUTHOR]

The contribution of each fragment of metal-organic frameworks (MOFs) to the adsorption of sulfur compounds were investigated using density functional theory (DFT). The involved sulfur compounds are dimethyl sulfide (CH 3 SCH 3 ), ethyl mercaptan (CH 3 CH 2 SH) and hydrogen sulfide (H 2 S). MOFs with different organic ligands (NH 2 -BDC, BDC and NDC), metal centers structures (M, M-M and M 3 O) and metal ions (Zn, Cu and Fe) were used to study their effects on sulfur species adsorption. The results revealed that, MOFs with coordinatively unsaturated sites (CUS) have the strongest binding strength with sulfur compounds, MOFs with NH 2 -BDC substituent group ligand comes second, followed by that with saturated metal center, and the organic ligands without substituent group has the weakest adsorption strength. Moreover, it was also found that, among different metal ions (Fe, Zn and Cu), MOFs with unsaturated Fe has the strongest adsorption strength for sulfur compounds. These results are consistent with our previous experimental observations, and therefore provide insights on the better design of MOFs for desulfurization application. [ABSTRACT FROM AUTHOR]

The supported Rh-based catalysts exhibit the excellent catalytic performances for syngas conversion to C 2 species. In this study, all possible elementary steps leading to C 2 species from syngas have been explored to identify the role of support and its surface hydroxyls over Rh/γ-Al 2 O 3 catalyst; Here, the results are obtained using density functional theory (DFT) method. Two models: Rh4 cluster supported on the dry γ-Al 2 O 3 (110) surface, D(Rh4), and on the hydroxylated γ-Al 2 O 3 (110) surface, H(Rh4), have been used to model Rh/γ-Al 2 O 3 catalyst. Our results show that CO prefers to be hydrogenated to CHO, subsequently, starting from CHO species, CH and CH 2 species are the dominate monomers among CH x ( x = 1–3) species rather than CH 3 and CH 3 OH on D(Rh4) and H(Rh4) surfaces, suggesting that γ-Al 2 O 3 -supported Rh catalyst exhibits the high selectivity towards CH x formation compared to the pure Rh catalyst. On the other hand, D(Rh4) is more favorable for C 2 hydrocarbon (C 2 H 2 ) formation, whereas H(Rh4) surface easily produces C 2 hydrocarbon (C 2 H 2 ) and C 2 oxygenates (CHCO,CH 2 CHO), indicating that the surface hydroxyls of support can affect the selectivity of C 2 species over Rh/γ-Al 2 O 3 catalyst in syngas conversion. Moreover, compared to the pure Rh(111) surface, Rh/γ-Al 2 O 3 catalyst can achieve the excellent catalytic performances for syngas conversion to C 2 species. [ABSTRACT FROM AUTHOR]

The adsorption of mercury species (Hg 0 , HgCl and HgCl 2 ) and catalytic oxidation of Hg 0 on the metal-loaded activated carbon (AC) with single Fe, Co, Ni, Cu and Zn atom have been studied using the periodic density functional theory (DFT) method. The results indicate that Hg 0 interacts with metal-loaded AC surfaces via a physical adsorption mechanism, while chemisorptions are likely adsorption mechanisms for HgCl and HgCl 2 . The existence forms of HgCl and HgCl 2 on metal-loaded AC surfaces are dissociated or molecular, which greatly depend on initial interaction modes between mercury species and surfaces. Besides, in the presence of Cl 2 , Hg 0 is oxidized to be HgCl 2 molecule on the Fe/AC surface, while dissociatively adsorbed HgCl 2 is predominant on Ni/AC, Cu/AC and Zn/AC surfaces, but both molecular and dissociated HgCl 2 exist on the Co/AC surface. What’s more, the kinetic results show that the oxidation energy barrier of Hg 0 on the Fe/AC surface is the lowest, implying that Fe-loaded AC is a favorable heterogeneous catalyst for Hg 0 oxidation from the point of view of efficiency and cost. [ABSTRACT FROM AUTHOR]

Water adsorption and dissociation on solid surfaces play a key role in a variety of industrial processes, a detailed comprehension of this process and the effect of the surface structure will assist in developing the improved catalysts. In this study, the adsorption and dissociation of H 2 O on three different types of CuO(111) surfaces, including the stoichiometric, oxygen-vacancy and oxygen-rich surfaces, have been systematically investigated and compared using density functional theory methods. All possible initial configurations of H 2 O adsorbed on those surfaces with only one coverage have been identified. Our results show that the adsorption ability of H 2 O is substantially weaker than that of the dissociated species (HO, H and O). H 2 O chemisorbs at the Cu SUB , Cu 2 and Cu SUB sites of the stoichiometric, oxygen-vacancy and oxygen-rich surfaces, respectively; subsequently, the chemisorption H 2 O dissociates into OH and H species. The dissociation mechanisms of chemisorption H 2 O and the single OH group leading to the final O and H species suggest that the dissociation of single OH species occurs at a higher barrier compared to the dissociation of OH in the presence of neighboring H atom (produced from the initial step of H 2 O dissociation), namely, the presence of H is in favor of OH dissociation, which agrees with the results of charge transfer. However, owing to the significantly high barrier of OH dissociation compared to the initial dissociation step of H 2 O, OH species is considered as the dominant product on those surfaces. Oxygen-rich surface is the most favorable for the initial dissociation of H 2 O both thermodynamically and kinetically than other two surfaces. The calculated vibrational frequencies for the adsorbed H 2 O and OH species on CuO(111) surfaces can be applied to guide the experimental research of surface vibrational spectroscopy. In addition, our results may provide a basis for the study of H 2 O interaction with other metal oxide surfaces. [ABSTRACT FROM AUTHOR]

Highlights: [•] CH2 coupling to C2H4 is a spontaneous reaction on Cu(211) in syngas conversion. [•] Cu catalyst favors hydrocarbons formation rather than C2 oxygenates. [•] M-doped Cu(211) (M=Rh, Ni) shows a better catalytic activity to C2 oxygenates. [•] C2 oxygenates is formed via CHO insertion into CH2 on M-doped Cu(211) (M=Rh, Ni). [•] The HOMO–LUMO gap is responsible for the difference between CO and CHO insertion. [ABSTRACT FROM AUTHOR]

Highlights: [•] CO+3H→CHO+2H→CH2O+H→CH3O are the optimal route for initial CO hydrogenation. [•] CH3OH formation is more favorable than CH3 on Cu(211) surface. [•] Cu(211) surface shows a better catalytic activity for C2H5OH rather than CH4. [•] Minimizing CH3OH and/or boosting CH3 can improve the productivity of ethanol. [•] Rh-decorated Cu catalyst can increase the productivity of ethanol from syngas. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hg0 is physically adsorbed on the perfect and oxygen-deficient ZnO surface. [•] HgS is strongly adsorbed on the perfect and oxygen-deficient ZnO surface. [•] The dissociated S by H2S can capture Hg0 to form HgS on the perfect surface. [•] The oxygen defect on the ZnO surface has not positive role in remove Hg0. [ABSTRACT FROM AUTHOR]

Highlights: [•] Both chemisorption and physisorption of molecular H2O exists on perfect surface. [•] Dissociative adsorption of H2O occurs predominantly on oxygen-vacancy surface. [•] H2O exists in the physisorption form on pre-covered oxygen surface. [•] Pre-covered oxygen can facilitate the dissociation of H2O into OH species. [•] OH species is energetically dominant product on these Cu2O(111) surfaces. [Copyright &y& Elsevier]

Abstract: The regeneration mechanisms of the sulfurized and oxygen-deficient ZnO(100) surfaces in an oxygen atmosphere have been systematically studied by using the density functional theory (DFT) method. An activation energy of 36.79kJ·mol−1 is needed for the regeneration of the sulfurized ZnO(100) surface at the GGA–PW91 functional level. The formed SO2 lies on the ZnO(100) surface horizontally, S in SO2 bonds to a surface oxygen atom to form an analogical SO3 structure. Two regeneration mechanisms are studied for the oxygen-deficient ZnO(100) surface. One is that O2 dissociatively adsorbs on the oxygen-deficient ZnO(100) surface leading to the regeneration of the surface. The other is that O2 molecularly adsorbs on the oxygen-deficient ZnO(100) surface, then a little activation energy of 29.43kJ·mol−1 is needed to make the surface regenerate. It can be concluded that the sulfurized and oxygen-deficient ZnO(100) surfaces are easy to be regenerated in an atmosphere containing O2. [Copyright &y& Elsevier]

Abstract: The interaction of Cu n (n =1–4) cluster with the dehydrated γ-Al2O3(110), hydrated γ-Al2O3(110) and dehydrated γ-Al2O3(100) surfaces has been systematically investigated to illustrate the influence of the hydroxylation of γ-Al2O3 surfaces on the stability and growth of Cu for Cu/γ-Al2O3 catalyst. Here, we present the main results obtained by the density functional theory together with slab model calculations. Our results show that the adsorption of Cu n (n =2–4) cluster on the γ-Al2O3(110) surface is more stable than that on the γ-Al2O3(100) surface, for the single Cu atom, the reverse becomes true. For the γ-Al2O3(110) surface, the adsorption of Cu n (n =2–4) cluster on the dehydrated surface is more stable than that on the hydrated surface due to the presence of the surface hydroxyls, however, the adsorption of the single Cu atom on the hydrated surface is more stable than that on the dehydrated surface due to the larger Cu–support interaction energy. On the other hand, compared to the γ-Al2O3(100) surface, the γ-Al2O3(110) surface is more favorable for the growth of Cu n clusters, in which the presence of surface hydroxyls reduces the growth ability of Cu n clusters. [Copyright &y& Elsevier]

Abstract: The mechanisms of CH x (x =1-3) formation from CO hydrogenation on Cu(111) surface have been systematically investigated using periodic density functional calculations. The activation barriers and reaction energies for all the elementary steps involved in CH x (x =1-3) formation is presented here. CO hydrogenation and its dissociation have been discussed. Our results show that the CO dissociation route is less energetically favored on Cu(111) surface than CO hydrogenation to form CHO and COH, in which CO mainly goes through hydrogenation to form CHO, meanwhile, the formation of CHO is more favorable both kinetically and thermodynamically than that of COH. Starting from CHO, we further investigate the formation of CH x (x =1-3), two conditions, without H-assisted and with H-assisted, are considered. As a result, we seek out the optimal paths of CH x (x =1-3) formation and the corresponding activation barrier of rate-controlled step on Cu(111) surface, moreover, among all CH x (x =1-3) species, CH2 and CH3 are the most favored monomer for CO hydrogenation on Cu(111). In addition, our results show that CH3OH is also easily formed by CO hydrogenation, and the formations of CH2, CH3 and CH3OH by CO hydrogenation compete with each other on Cu(111) surface. [Copyright &y& Elsevier]

Abstract: The elementary steps leading to the formation of HCOO and CO via CO2 hydrogenation, two important intermediates contributing to methanol and methane formation, respectively, have been explored to identify hydroxylation effect of the oxide support on the selectivity in CO2 hydrogenation on Pd/γ-Al2O3 catalyst by the density functional theory together with slab model calculations. Two models: tetramer Pd4 cluster supported on the dry γ-Al2O3(110) surface, D(Pd4), and on the hydroxylated γ-Al2O3(110) surface, H(Pd4), have been employed to model Pd/γ-Al2O3 catalyst. Meanwhile, Pd(111) surface is used to model the unsupported large Pd particle sizes. On D(Pd4), the formation of CO is preferred both kinetically and thermodynamically. On H(Pd4), HCOO formation becomes more favorable kinetically while CO formation is more facile thermodynamically. However, Pd(111) surface has not shown strong selectivity and activity for CO2 hydrogenation to HCOO or CO. These results show that varying the properties of γ-Al2O3 support can alter the selectivity of CO2 hydrogenation, moreover, the presence and number of low-coordinated Pd particles is of great importance to improve the overall activity and selectivity of CO2 hydrogenation. Our results also show that to achieve high selectivity of CO2 hydrogenation, Pd/γ-Al2O3 catalyst has to get help from additives, which should be able to improve its dispersion or to control the hydroxylation. The present study provides the basis and one of the directions to the design of improved catalysts in CO2 hydrogenation for methanol, methane and other products. [Copyright &y& Elsevier]

Abstract: The adsorption and dissociation of O2 on CuCl(111) surface have been systematically studied by the density functional theory (DFT) slab calculations. Different kinds of possible modes of atomic O and molecular O2 adsorbed on CuCl(111) surface and possible dissociation pathways are identified, and the optimized geometry, adsorption energy, vibrational frequency and Mulliken charge are obtained. The calculated results show that the favorable adsorption occurs at hollow site for O atom, and molecular O2 lying flatly on the surface with one O atom binding with top Cu atom is the most stable adsorption configuration. The O–O stretching vibrational frequencies are significantly red-shifted, and the charges transferred from CuCl to oxygen. Upon O2 adsorption, the oxygen species adsorbed on CuCl(111) surface mainly shows the characteristic of the superoxo (O2 −), which primarily contributes to improving the catalytic activity of CuCl, meanwhile, a small quantity of O2 dissociation into atomic O also occur, which need to overcome very large activation barrier. Our results can provide some microscopic information for the catalytic mechanism of DMC synthesis over CuCl catalyst from oxidative carbonylation of methanol. [Copyright &y& Elsevier]

Abstract: DFT calculations have been performed to investigate the effect of dielectric responses of the solvent environment on the CO adsorption over CuCl(111) surface by using COSMO (conductor-like solvent model) model in Dmol3. Different dielectric constants, including vacuum, liquid paraffin, methylene chloride, methanol and water solution, are considered. The effects of solvent model on the structural parameters, adsorption energies and vibrational frequency of CO adsorption over CuCl(111) surface have been investigated. The calculation results suggest that solvent effects can improve the stability of CO adsorption and reduce the intensity of C–O bond, which might mean that solvent is in favor of C–O bond activation and improve the reaction activity of oxidative carbonylation in a slurry reactor. [Copyright &y& Elsevier]

• The support type and cluster size affect catalytic performance of C 2 H 2 semi-hydrogenation over the catalysts with carbon material supported metal clusters. • Pd 1 /GDY catalyst exhibits the best C 2 H 4 selectivity and activity. • The average Mulliken charge of metal atoms affects C 2 H 4 selectivity and activity. • Pd 1 /GDY with excellent performance is attributed to the moderate Mulliken charge of metal Pd. • The valuable clues for the design of carbon material supported metal cluster catalysts are provided. The support type and cluster size of the supported catalysts strongly affect their catalytic performance toward the targeted reaction. This study is designed to investigate the influences of support type and cluster size on C 2 H 4 selectivity and activity of C 2 H 2 semi-hydrogenation; density functional theory calculations were utilized to illustrate C 2 H 2 semi-hydrogenation mechanism on the catalysts with the different carbon material supported different sizes of metal clusters. The results show that for the different carbon material supported single-atom Cu or Pd catalysts, the support types greatly affect C 2 H 4 selectivity and activity, among them, GDY support shows excellent catalytic performance. On the other side, as to the M n /GDY (M=Cu, Pd) catalysts with different cluster sizes, the activity of Pd n /GDY is generally better than that of Cu n /GDY; while the selectivity of Cu n /GDY is better than that of Pd n /GDY. Interestingly, Pd 1 /GDY presents excellent C 2 H 4 selectivity and activity for C 2 H 2 semi-hydrogenation, attributing to its moderate Mulliken charge of metal atoms. This study could provide valuable structure clue for the obtaining of highly-efficient supported catalysts with suitable carbon material support and cluster size. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The Zn2+/HZSM-5 catalyst with Zn2+ at T5-T3 site exhibits excellent dehydrogenation performance. • Brønsted acid site shows higher activity for cyclization than Lewis acid site. • The Lewis acid enhances the strength of Brønsted acid. • The stronger Brønsted acid strength, the cyclization easier occur. • The favorable route for the benzene formation on Zn2+/HZSM-5 with the highest TOF base on the microkinetic analysis. The Zn modified HZSM-5 (Zn2+/HZSM-5) has emerged as effective catalysts for the methanol to aromatics (MTA) reaction, owing to its superior activity and selectivity in producing the desired target products. The intricacies of the internal environment within Zn2+/HZSM-5, have led to uncertainties regarding active centers responsible for dehydrogenation and cyclization reactions. In this study, we investigate the active centers involved in the dehydrogenation and cyclization reactions during the aromatization of long-chain C6 mono-olefins over the Zn2+/HZSM-5 catalyst using density functional theory (DFT) method. Our findings reveal that for dehydrogenation, the Lewis acid site (Zn2+) serves as the active center. Specifically, Zn2+ located at the T5-T3 site exhibits optimal dehydrogenation activity due to its lower energy barrier, more Mulliken charge transfer, and a smaller energy barrier gap between the high occupied molecular orbit and the low occupied molecular orbit. In addition, for cyclization, the active center is identified as the Brønsted acid site. Remarkably, the Zn2+/H-Al-ZSM-5 (Zn2+ at T5-T3 site) catalyst exhibits superior cyclization activity with the strongest Brønsted acid strength. The dehydrogenation and 1,6 ring closure process of n -hexene for benzene formation on Zn2+/HZSM-5 possesses the highest TOF based on the microkinetic analysis. This study offers valuable theoretical insights that can guide the exploration and development of catalysts for the aromatization of long-chain C6 olefins. [ABSTRACT FROM AUTHOR]

The effect of Zr on the framework structure and acid strength of doped H-SAPO-34 and H-ZSM-5 was studied using the density functional theory considering dispersive interactions (DFT-D2). The activity and selectivity in methanol-to-olefins (MTO; in this work, olefins refer to ethylene and propylene) conversion over Zr doped H-SAPO-34 and H-ZSM-5 were systematically evaluated as a function of frameworks' structure and acid strength. The results were compared with those of their non-doped counterparts. The results indicated that doping of Zr into H-SAPO-34 exhibited larger pore volume, whereas the doping of Zr into H-ZSM-5 had little effect on pore volume. The acid strengths of both the Zr doped were reduced. It was found that doping of Zr into H-SAPO-34 led to enhanced activity, whereas doping of Zr into H-ZSM-5 had either little or no effect on activity. It can be concluded that the steric constraints, exerted by the larger cavity, are favorable for the MTO conversion. Both Zr doped H-SAPO-34 and H-ZSM-5 exhibited relatively higher ethylene selectivity. The acid strength of is closely related to the product selectivity during MTO conversion. The catalysts with weaker acid strengths displayed a higher selectivity towards ethylene. The activity and selectivity for MTO conversion to ethylene and propylene over altered topological molecular sieve structure are studied. Unlabelled Image • The Zr incorporation in molecular sieve framework can be used to modify the acid properties of molecular sieve. • Different cavity-structured molecular sieves present different catalytic activity for MTO conversion. • The weak acid strength of molecular sieves presents higher selectivity towards ethylene. [ABSTRACT FROM AUTHOR]

The mechanisms of dehydrogenation reactions as important processes in methanol to aromatics (MTA) have been controversial. Recent work on the active center for dehydrogenation at either Lewis acid site (LAS) or Brønsted−Lewis (B−L) acid synergistic site is a matter. The dehydrogenation processes on L−acid site (GaO+) or B−L acid site (H+ − GaO+) over GaO+/HZSM-5 with different Lewis acid locations for n -hexene to 1,5-hexadiene, as well as cyclohexene to benzene have been researched by applying the density functional theory (DFT) method. The results reflect that active center of dehydrogenation reactions is B−L acid synergistic site through B−L acid synergy mechanism. All elementary steps including C−H bond activation, the formation of H 2 , hydrogen transfer as well as the regeneration of B−acid site are easy to proceed. However, the isomerization for carbonium ions from GaO+ to skeleton oxygen of zeolites is relatively difficult. The analysis shows that isomerization is influenced by the structural and electronic properties of carbonium ions chemisorbed on zeolites. Lewis acid strength of GaO+/HZSM-5 and energy gap between HOMO and LUMO on adsorption complexes are appropriate descriptors for the C−H bond activation. The rate constants analysis indicates that increasing temperature is more favorable for C−H bond activation. Further considering that C−H bond activation occurred preferentially than isomerization, it could be a critical initial step to primarily screen catalysts. [Display omitted] • The active center of dehydrogenation is B−L acid (H+−GaO+) synergistic site. • C−H bond activation and isomerization are key processes. • Lewis acid strength and energy gap are descriptors for C−H bond activation. [ABSTRACT FROM AUTHOR]

• Rh 1 Ni 1 (111) is screened out to present excellent catalytic performance. • Introduction of Ni promotes CO conversion and increases CH x concentration. • Ethanol selectivity and generation activity exhibit a volcanic-type relationship with d band center. • 1Rh1Ni/γ-Al 2 O 3 present higher CO conversion rate and ethanol yield. The direct conversion of syngas to ethanol faces challenges due to catalyst inefficiencies and low ethanol yield. Bulk alloys with an appropriate atomic ratio can exhibit excellent catalytic performance. In this work, a series of Rh x Ni y (111) with different Rh/Ni ratios was rationally designed, and the ethanol preparation from syngas was explored based on density functional theory (DFT) calculation and microkinetic analysis. The results show that Rh 1 Ni 1 (111) was screened out to show optimum catalytic performance for ethanol production. This was attributed to a moderate quantity of charge transfer from Ni to Rh atoms, and a medium distance from the d -band center to the Fermi level. Further, to verify the catalytic performance of the catalysts at a Rh: Ni ratio of 1: 1, 1Rh1Ni/γ-Al 2 O 3 catalyst was prepared and its catalytic performance for ethanol preparation from syngas was investigated by comparing it with that of Rh/γ-Al 2 O 3 and Ni/γ-Al 2 O 3. The catalytic performance of 1Rh1Ni/γ-Al 2 O 3 has been further confirmed to be preferred over Rh/γ-Al 2 O 3 and Ni/γ-Al 2 O 3 , achieving a 23.0 % CO conversion rate with 31.2 % ethanol selectivity. [Display omitted] [ABSTRACT FROM AUTHOR]

• The reaction mechanism of generating 2 c ,2 t -dimethyladamantane is validated to be reasonable. • The activity of HAlY zeolite with strong brønsted acid strength is superior. • The weaker lewis acid strength contributes to stronger brønsted acid strength. • The existence of lewis acid with oxoaluminum cations enhances the reactive activity. The adamantane derivatives are promising high-energy-density fuel due to preferable fuel properties, the activity of HY zeolite is key for synthesis adamantane derivatives on account of easy separation from liquid fuels. The effect of acid strength and type of zeolite on activity from DMTCD to 2 c ,2 t -dimethyladamantane is investigated by the DFT method. The activity on HAlY zeolite with stronger Brønsted acid strength is superior compared to HGaY, HFeY, HInY and HBY. Thus, AlO+ / HAlY zeolite is investigated obtaining that smaller gap between LUMO and HOMO leads to the better activity than HAlY. And oxoaluminum cations as Lewis acid improves Brønsted acid strength, in which the activity of AlO+/HAlY with stronger Brønsted/weaker Lewis acid strength is preferable than other HAlY with Lewis acid. Therefore, this work provides guidance for screening of HY zeolite with preferable activity of hydro-isomerization. [Display omitted] [ABSTRACT FROM AUTHOR]

• The CH 2 and CH 3 are the most advantageous monomers on the S-Cu(100) catalyst. • The OHCCHO is also a key intermediate to synthesize ethanol and ethylene glycol. • The charge transfer between Cu and S increases the syngas to C 2 oxygenates. Low-cost catalysts based on Cu have emerged as promising catalysts for synthesizing ethanol from syngas, despite their limited selectivity to ethanol. This study investigates sulfur-modified Cu(100) surface for converting syngas to C 2 oxygenates, and explores the intricate mechanism of C 2 oxygenates formation from CO hydrogenation using density functional theory (DFT) calculations. The findings indicate that the CH 2 and CH 3 are the most advantageous monomers over other CH x (x = 1–3) intermediates, surpassing methanol and methane formation. This result significantly differs from observations on the Cu(100) surface. For C 2 oxygenates formation, the most effective pathway involves the insertion of CHO into CH 3 or CHO via C–C to generate a stable intermediate CH 3 CHO and OHCCHO on the S-Cu(100) surface. Additionally, the examination of electrical and structural characteristics reveals a mild charge transfer between Cu and S, which enhances the catalytic performance for syngas to C 2 oxygenates. Therefore, this work provides valuable insights into the role of sulfur-modified Cu(100) surface in enhancing the selectivity to C 2 oxygenates. [Display omitted] [ABSTRACT FROM AUTHOR]

The hydrogen transfer reaction is one of the main source of byproducts alkanes from methanol to aromatics resulting in reducing the aromatics selectivity. The hydrogen transfer reactions between two linear alkenes were systematically investigated utilizing the density functional theoretical method on clean H-ZSM-5 and [GaH]2+ from Ga modified ZSM-5. The results show that the [GaH]2+ species on Ga-ZSM-5 is favorable for the hydrogen transfer reaction in MTA. In addition, TOF of hydrogen transfer decreases with the increase of temperature on [GaH]2+ from Ga-ZSM-5. The insights in this work will be of great significance to understand the hydrogen transfer mechanism catalyzed by metal modified zeolite. [Display omitted] • [GaH]2+ is favorable for hydrogen transfer reaction. • The mechanisms of hydrogen transfer reactions on clean and Ga modified ZSM-5 are elucidated. • TOF of hydrogen transfer decreases with the increase of temperature on [GaH]2+ from Ga-ZSM-5. [ABSTRACT FROM AUTHOR]

• The heteronuclear DACs (MoX@NC) possesses higher catalytic ability than the homonuclear DACs (2X@NC). • Compared to the homonuclear DACs, the Bader charge indicates that the electronic interaction between Mo atom and other transition metals is enhanced for the heteronuclear DACs. • The synergistic effect of the heteronuclear DACs originates from the enhancement of the intermetallic interaction between Mo atom and other transition metals in dimer. In order to identify the synergistic effect in the heteronuclear double-atom catalysts (DACs) on CO activation, the homonuclear and heteronuclear DACs have been designed based on graphene supporter. And the three CO dissociation pathways have been considered using the density functional theory (DFT) calculation. It reveals that the heteronuclear DACs (MoX@NC) possesses higher catalytic ability than the homonuclear DACs (2X@NC) for CO activation. And the unpaired d -orbital electron plays a significant role on CO activation, which can change the magnetic moment of the DACs. The coordination atoms offer similar local coordination environment for the homonuclear and heteronuclear DACs. However, the Bader charge displays that there is a strong electronic interaction between Mo atom and other transition metals of dimer for the heteronuclear DACs. The synergistic effect of the heteronuclear DACs originates from the enhancement of the intermetallic interaction between the Mo atom and other transition metals. The work offers rational guideline for the synthesis of DACs with excellent catalytic performances, and has great potential for application in various catalytic fields. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • The activity of H 2 dissociation increases with the size increasing of Pd-doped Cu cluster. • Pd ensemble as active center consisted of outermost and its contiguous sub-layer Pd atoms. • The activity of H 2 dissociation increases with the size increasing of doped Pd ensemble. • Pd ensemble forms the electron-rich regions to enhance the activity of H 2 dissociation. • The shell Cu atom replaced by Pd atom should be focused on the higher coordination Cu. Aiming at probing into the effects of cluster size and Pd ensemble as active center on H 2 dissociation over Pd-doped Cu bimetallic cluster, density functional theory calculations are employed to investigate H 2 adsorption and dissociation over the Cu and Pd-doped Cu clusters with different sizes. The results show that compared to Cu cluster, the doped Pd atom and its ensemble composed of outermost layer and its connected sub-layer Pd atoms as active center greatly enhance catalytic activity of H 2 dissociation at the same size of Pd-doped Cu clusters, which is attributed to the interaction enhancement between H 2 and the clusters since d -band centers gradually approach the Fermi level and the electron-rich regions are formed around Pd ensemble. Moreover, among the Pd-doped Cu clusters with different sizes, the Bader charge indicate that when the number of doped-Pd atoms is same, the amount of charge on Pd ensemble increases with the size increasing of Pd-doped Cu catalysts, the cluster with larger size is beneficial for promoting the activity of H 2 dissociation; thus, the size effect of Pd-doped Cu cluster on H 2 dissociation is dominantly attributed to the electronic effect. This work not only provides a valuable clue for evaluating catalytic activity of other promoter metal-doped Cu catalysts for H 2 dissociation, but also gives out the ways that adjusting the cluster size and the promoter ensemble can facilitate the dissociation of H 2 atoms as an initially key step in the heterogeneous hydrogenation. [ABSTRACT FROM AUTHOR]

• A newly so-called CH x self-promoting syngas conversion mechanism has been proposed. • This study revealed for the first time the new role of surface adsorbed CH x intermediates. • CH x (x = 1–3) intermediates itself as a self-promoter facilitate CO conversion to form C 2 oxygenates. • The dominant CH 2 monomer as a self-promoter plays an important role. • CH 2 monomer promotes itself formation and C 2 oxygenates instead of methanol and hydrocarbons. Syngas conversion to C 2 oxygenates includes two crucial steps that CO activation to form CH x (x = 1–3) intermediates, followed by its reaction with CO/CHO to form the C C chain, in which the CH x (x = 1–3) intermediates were widely recognized as the reactive intermediates to yield C 2 oxygenates. Inspired by the reported studies about the role of co-adsorbed OH intermediates that promote CO activation and the C C chain formation in syngas conversion, an idea about the new role of surface adsorbed CH x intermediates in syngas conversion is proposed, that is, whether the surface adsorbed CH x intermediates itself also act as a co-adsorbed promoter to self-promote CO activation and conversion. This study revealed for the first time that in syngas conversion to C 2 oxygenates over Rh-doped Cu catalysts, the surface adsorbed CH x (x = 1–3) intermediates not only act as the reactive intermediates to participate into the reactions with CO/CHO, but also itself act as a self-promoter to facilitate CO activation to form CH x (x = 1–3) intermediates and promote CHO reaction with CH x (x = 1–3) to form C 2 oxygenates. Especially, the dominant CH 2 intermediate acted as a co-adsorbed promoter exhibits higher activity and selectivity towards itself formation and C 2 oxygenates CH 2 CHO instead of methanol and hydrocarbons, respectively. Moreover, the internal mechanism of surface adsorbed CH x intermediate is explained from the electronic property aspect. This newly so-called CH x self-promoting syngas conversion mechanism offers new insights into the fundamental role of surface adsorbed CH x (x = 1–3) intermediates in CO activation and conversion to form C 2 oxygenates, and open a new mechanism that is likely general and involved in the reactions related to CH x (x = 1–3) intermediates formation. [ABSTRACT FROM AUTHOR]

Abstract Developing low amount and high catalytic performance of Pd-based catalysts are vital for the oxidation of CO to dimethyl oxalate (DMO) in industry. In this study, Pd stripe and Pd single atom-doped Cu(111) surfaces are constructed via Pd substituting four striped Cu atoms and single Cu atom of surface layer over the Cu(111) surface, respectively, namely Pd 4 Cu 8 /Cu(111) and Pd 1 -Cu(111) surfaces, and two possible reaction pathways related to DMO synthesis have been studied on two surfaces employing density functional theory (DFT) calculation in combination with microkinetic analysis and subsequently compared with the cases of Pd(111) and Pd ML /Cu(111). The results show that COOCH 3 -COOCH 3 coupling pathway is superior to COOCH 3 -CO on Pd 4 Cu 8 /Cu(111) and Pd 1 -Cu(111). Moreover, the Pd 1 -Cu(111) surface shows highest catalytic activity for DMO generation, followed by the Pd 4 Cu 8 /Cu(111), the Pd(111) and the Pd ML /Cu(111) surface. Additionally, Pd 4 Cu 8 /Cu(111) and Pd 1 -Cu(111) surfaces exhibit high DMO selectivity. Thus, Pd stripe and Pd single atom-doped Cu(111) surfaces are thought to be prospective candidates to improve the catalytic performance of noble Pd and reduce its usage for CO oxidation to DMO. Graphical abstract Unlabelled Image Highlights • The COOCH 3 -COOCH 3 coupling is the optimal route on Pd 4 Cu 8 /Cu(111) and Pd 1 -Cu(111) surfaces. • The activity for DMO formation is in sequence of Pd 1 -Cu(111) > Pd 4 Cu 8 /Cu(111) > Pd(111) > Pd ML /Cu(111). • Pd 4 Cu 8 /Cu(111) and Pd 1 -Cu(111) surfaces are proposed to be prospective candidates for DMO formation. [ABSTRACT FROM AUTHOR]

• CO atmosphere promotes Cu surface diffusion significantly. • H 2 atmosphere influences on Cu surface diffusion weakly. • Ppm H 2 S significantly promotes Cu surface diffusion at different temperature. • Cu surface performs lower H 2 S tolerance, according with the experimental results. • The study provides the microscopic reason that ppm H 2 S lead to Cu sintering. Understanding the diffusion mechanism of Cu cluster over Cu surface is one of the important issues to predict and improve the stability of Cu-based catalyst. The diffusion of Cu adatom, Cu 2 and Cu 3 cluster over Cu(111) surface under different atmospheres (vacuum, CO, H 2 and H 2 S atmosphere) at different temperatures have been investigated using density functional theory calculations. The results suggest that CO accelerates Cu surface diffusion at different temperatures, while H 2 atmosphere has little effect depending on the temperature. Further, under H 2 S atmosphere, the negative formation energy of Cu-S complexes indicate that Cu-S species are more facile to form on Cu(111) surface. The diffusivity of CuS complex increases significantly with the decreasing of temperature and the increasing of H 2 S concentration, which suggests that ppm H 2 S results in the fast sintering of Cu surface significantly. This is consistent with the experimental result. [ABSTRACT FROM AUTHOR]

[Display omitted] • CO at bridge or hollow site participates in the DMO formation on the Pd(100). • Top- and bridge-CO is consumed during CO oxidative coupling on Pd(110) and (211). • Pd(100) exhibits high activity for CO oxidation coupling to DMO. • The favorable path to DMO on Pd(100) surface is COOCH 3 -COOCH 3 pathway. CO oxidative coupling to dimethyl oxalate (DMO) on Pd(100), (110) and (211) surfaces have been investigated through the density functional theory (DFT) method together with periodic slab models. Effect of different surface structures on adsorption, reaction and catalytic activity has been explored. CO at different adsorption sites participated in the oxidative coupling reaction according to the surface structure. CO at bridge or hollow site was consumed for the coupling reaction on the Pd(100) surface, and the favorable route was COOCH 3 -COOCH 3 coupling path. While CO-COOCH 3 coupling route was the optimal on Pd(110) and (211) surfaces, CO at top and bridge site took part in the reaction, respectively. Pd(100) surface exhibited higher catalytic activity and selectivity to DMO than Pd(110) and (211) surfaces. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • PdIn with single-atom Pd sites exhibits better selectivity toward HCOOH oxidation to CO 2. • Pd 3 In with the Pd trimer presents better selectivity toward the formation of CO. • CO poisoning is remarkably reduced on PdIn catalysts with isolated single-atom Pd sites. • PdIn intermetallic exhibits better activity toward CO 2 formation than the pure Pd. Abstract Isolated single-atom Pd sites in intermetallic structures have the higher stability and unique catalytic properties. This study was designed to investigate the properties of isolated single-atom Pd sites in PdIn intermetallic toward formic acid oxidation compared to Pd 3 In and the pure Pd using density functional theory calculation. Unexpectedly, CO adsorption over PdIn catalyst is significantly lower than those over Pd 3 In and the pure Pd catalysts, an indication that CO poisoning is remarkably reduced on PdIn catalysts compared to the Pd 3 In and pure Pd catalysts. More importantly, PdIn catalyst with isolated single-atom Pd sites exhibits higher selectivity for formic acid oxidation to CO 2 and inhibits CO formation, whereas Pd 3 In catalyst with Pd trimer presents better selectivity for formic acid oxidation to CO, which poisons Pd-based catalyst. Moreover, compared to the pure Pd catalyst, PdIn catalyst with isolated single-atom Pd sites not only has the higher activity and stability but also maximize atomic efficiency for noble metal Pd to reduce the catalyst cost. It is expected that the method applied in this research is beneficial to for the design and evaluation of intermetallic catalysts in clean energy technology development. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • CO oxidative coupling on Pd 4 /TiO 2 and Pd 4 /TiO 2 -O v were studied by DFT method. • The stronger interaction between Pd 4 and TiO 2 -O v than Pd 4 and TiO 2. • Pd 4 /TiO 2 -O v exhibits a high activity for CO oxidative coupling to DMO. Abstract The reaction mechanisms for CO oxidative coupling to DMO on Pd 4 supported on TiO 2 (0 0 1) catalysts were studied by using the density functional theory calculations with a Hubbard U correction (DFT + U). Two different supports including perfect TiO 2 (0 0 1) and oxygen vacancy TiO 2 (0 0 1) were investigated. The interaction between Pd 4 and supports showed that the binding energy of Pd 4 cluster with oxygen vacancy TiO 2 (0 0 1) was stronger than that with the perfect TiO 2 (0 0 1), and the relatively weak adsorption energy of CO was obtained on Pd 4 /TiO 2 -O v , implied that it was easier for CO removing and reacting. In addition, reaction mechanisms of CO oxidative coupling to DMO on Pd 4 /TiO 2 and Pd 4 /TiO 2 -O v were studied, and the Pd 4 /TiO 2 -O v catalyst showed higher activity than Pd 4 -TiO 2. Moreover, compared with Pd(1 1 1), Pd 4 /TiO 2 -O v not only reduced the amount of Pd, but also improved the activity of CO oxidative coupling to DMO. However, DMO and DMC were competitive products on Pd 4 /TiO 2 and Pd 4 /TiO 2 -O v , showed that they were with poor selectivity to DMO. [ABSTRACT FROM AUTHOR]

The methylation of toluene with methanol is an important process for the preparation of p-xylene (PX). The modification of Ni-containing species in HZSM-5 can improve the yield of PX. However, the active site existence form of Ni is unclear. The intrinsic reaction mechanisms for methylation of toluene with methanol over HZSM-5 with NiOH+ and Ni2+ as Lewis acid have been investigated. The results indicate that the introduction of Ni2+ decreases the activity for the methanol dissociation, whereas NiOH+ enhances the activity with a reduction in activation energy of 100.7 kJ/mol. Furthermore, the generation of three xylenes, as well as the conversion of PX to 1,2,4-Trimethylbenzene (1,2,4-TMB) have also been studied over NiOH+/HZSM-5. It is shown that PX is most easily formed with the lowest energy barrier of 84.8 kJ/mol in four products, implying the introduction of NiOH+ in HZSM-5 favors the formation of PX. In addition, molecular dynamics simulations show that toluene reacts with methanol to form xylenes mainly at the intersection of channels. PX exhibits a much higher self-diffusion coefficient than MX and OX when the temperature rises from 498 to 698 K. It can be concluded that NiOH+ is the active Ni-containing species and NiOH+/HZSM-5 is an excellent catalyst for the production of PX via the methylation of toluene with methanol. [Display omitted] • NiOH+/HZSM-5 has high activity for methanol dissociation. • The lower activation energy is needed for PX formation than that for MX, OX and 1,2,4-TMB. • The more negative charge methanol receives, the more easily it dissociates. • NiOH+/HZSM-5 (T7-2) exhibits excellent channel shape selectivity to PX. [ABSTRACT FROM AUTHOR]

• C 2 H 2 semi-hydrogenation catalytic performance closely depends on Pd n cluster size. • CO introduction inhibits green oil production over Pd n /TiO 2 catalysts. • The activation barriers of C 2 H 4 hydrogenation can predict C 2 H 4 selectivity. • The activation barriers of C 2 H 3 coupling can predict the selectivity of green oil. • Both Pd 4 /TiO 2 and Pd 2 CO/TiO 2 are screened out to be the most suitable catalysts. The size effect of Pd catalyst and CO as a selective accelerator in C 2 H 2 semi-hydrogenation over Pd catalyst are two main factors to affect catalytic performance. In this work, density functional theory calculations were used to unravel the roles of Pd cluster size and introduced CO over the anatase TiO 2 supported Pd n (n = 2, 3, 4, 7, 13) clusters in tuning catalytic performance of C 2 H 2 semi-hydrogenation. The results show that as the increasing of Pd n cluster size over Pd n /TiO 2 catalysts, C 2 H 4 selectivity generally presents a volcanic-type curve, and the activity of C 2 H 4 and green oil presents an inverted volcanic-type curve. Compared with Pd n /TiO 2 catalysts, the introduction of CO greatly improves C 2 H 4 selectivity over Pd 2 /TiO 2 and Pd 3 /TiO 2 catalysts, enhances C 2 H 4 formation activity over Pd n /TiO 2 (n = 3, 4, 7, 13), and decreases green oil production over Pd 2 /TiO 2 and Pd 13 /TiO 2 catalysts. Meanwhile, the activation free energy of C 2 H 4 hydrogenation and C 2 H 3 coupling reaction can be used as the evaluate index to quantitatively predict the selectivity of C 2 H 4 and green oil, respectively. The different geometric and electronic effects induced by the introduction of CO could tune catalytic performance. The screened Pd 4 /TiO 2 and Pd 2 CO/TiO 2 catalysts are the most suitable catalysts in the Pd n /TiO 2 and Pd n CO/TiO 2 catalysts, respectively. The relationship of Pd n cluster size and CO introduction with C 2 H 4 selectivity and formation activity would provide valuable structural clue for the construction of C 2 H 2 semi-hydrogenation catalyst with highly catalytic performance. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The COOCH 3 -COOCH 3 coupling is the favorable path on Pd ML /Co(1 1 1) and Pd ML /Ni(1 1 1) surfaces. • The catalytic activity of these catalysts follows the trend of Pd ML /Co(1 1 1) > Pd ML /Ni(1 1 1) > Pd(1 1 1). • Pd ML /Ni and Pd ML /Co bimetallic catalysts can enhance the catalytic performance and reduce cost. Abstract Pd ML /Ni(1 1 1) and Pd ML /Co(1 1 1) surfaces were built via Pd atoms substituting the upper one layer atoms of Ni(1 1 1) and Co(1 1 1) surfaces, and have been discussed toward dimethyl oxalate (DMO) synthesis using density functional theory (DFT) calculation and micro-kinetic modeling, which were further compared with the Pd(1 1 1) surface, in order to obtain high cost-efficiency Pd-based bimetallic catalysts. The results suggest that CO + OCH 3 → COOCH 3 + (CO + OCH 3) → 2COOCH 3 → DMO is the favorable route and 2COOCH 3 → DMO is the rate-determining step on Pd ML /Ni(1 1 1) and Pd ML /Co(1 1 1) surfaces, and it is the same as that over the Pd(1 1 1) surface. The energy barriers combining with micro-kinetic modeling analysis show that the catalytic activity toward DMO synthesis follows the trend of Pd ML /Co(1 1 1) > Pd ML /Ni(1 1 1) > Pd(1 1 1). Moreover, DMO generation is superior to the formation of by-product DMC over Pd ML /Ni(1 1 1) and Pd ML /Co(1 1 1) surfaces. Therefore, Pd ML /Ni and Pd ML /Co bimetallic catalysts are proposed to be promising candidates for DMO formation. [ABSTRACT FROM AUTHOR]