Influence of surface strain on activity and selectivity of Pd-based catalysts for the hydrogenation of acetylene: A DFT study

On the nature of Cu-carbon interaction through N-modification for enhanced ethanol synthesis from syngas and methanol

Direct conversion of syngas into ethanol is an attractive process because of its short route and high-added value, but remains an enormous challenge due to the low selectivity caused by unclear active sites. Here, the Cu(111) supported N-modified graphene fragments C13-mNm/Cu(111) (m = 0-2) are demonstrated to be an efficient catalyst for fabricating ethanol from syngas and methanol. Our results suggest that the Cu-carbon interaction not only facilitates CO activation, but also significantly affects the adsorption stability of C2 intermediates and finally changes the fundamental reaction mechanism. The impeded hydrogenation performance of C13/Cu(111) due to the introduced Cu-carbon interaction is dramatically improved by N-doping. Multiple analyses reveal that the promoted electron transfer and the enhanced electron endowing ability of C13-mNm/Cu(111) (m = 1-2) to the co-adsorbed CH3CHxOH (x = 0-1) and H are deemed to be mainly responsible for the remarkable enhancement in hydrogenation ability. From the standpoint of the frontier molecular orbital, the decreased HOMO-LUMO gap and the increased overlap extent of HOMO and LUMO with the doping of N atoms also further verify the more facile hydrogenation reactions. Clearly, the Cu-carbon interaction through N-modification is of critical importance in ethanol formation. The final hydrogenation reaction during ethanol formation is deemed to be the rate-controlling step. The insights gained here could shed new light on the nature of Cu-carbon interaction in carbon material modified Cu-based catalysts for ethanol synthesis, which could be extended to design and modify other metal-carbon catalysts.

Strain Effect on Adsorption and Reactions of AHx (A = C, N, O, X £ 3) on In2O3(110), TiO2(110) and ZrO2(101) Surfaces

More and more attention has been paid to strain-based regulation of catalytic activity. To guide regulation of catalytic performance via strain engineering, adsorption and reactions of AHx (A = C, N, O, x £ 3) were investigated on uniformly strained In2O3 (110), rutile TiO2 (110) and tetragonal ZrO2 (101) from -2% to 4%. The results show that adsorption energies vary linearly with strain; expansive strain enhances adsorption of most adsorbates. Unlike the adsorbate scaling relations which are central atom dependent, the adsorbate scaling relations on strained surfaces are central atom independent. C-H/O-H bonds are elongated/shortened with expansive strain, and adsorption energies of CHx generally change more than those of OHx and NHx, which can be rationalized with effective medium theory and pertinent bond energies. Thermodynamically In2O3(110)/ZrO2(101) is most active/inactive. The estimated variation of rate constants at 300K from 0% to 2% strain based on Brønsted−Evans−Polanyi relationship demonstrates great strain regulation potential of catalytic performance on these oxide surfaces. Finally it is demonstrated that strain tends to facilitate the reactions whose sum of stoichiometric number is positive, which can be used as a rule to guide strain engineering for heterogeneous catalysis.

Rationalization of Nonlinear Adsorption Energy-Strain Relations and Brønsted-Evans-Polanyi and Transition State Scaling Relationships under Strain

Scaling relations play a vital role in high-throughput screening of catalytic materials, and more and more attention is being paid to strain-based regulation of catalytic performance. Here we investigated the variation of several energetics, including adsorption energies in the initial state, transition state, and final state, reaction energies, and energy barriers with strain, by studying CO, BH, NH, CH, and NO adsorption and dissociation on M(111) (M = Cu, Ag, Ni, Pd, or Pt) surfaces. We show that energy barriers, reaction energies, and adsorption energies can vary either linearly or nonlinearly (quadratically) with strain. Systems with stronger adsorbate-substrate interaction and weaker atom-atom interaction in substrates are more likely to exhibit nonlinear relations. The well-known Brønsted-Evans-Polanyi relationships and transition state scaling relationships under strain were also examined, and both of them can be nonlinear under strain, in principle. The observed nonlinear relationships were satisfactorily rationalized with the equations derived from Mechanics of Solids.

Strong Metal-Support Interactions between Pt Single Atoms and TiO2

Strong metal-support interaction (SMSI) has gained great attention in the field of heterogeneous catalysis. However, whether single-atom catalysts can exhibit SMSI remains unknown. Here, we demonstrate that SMSI can occur on TiO₂ -supported Pt single atoms but at a much higher reduction temperature than that for Pt nanoparticles (NPs). Pt single atoms involved in SMSI are not covered by the TiO₂ support nor do they sink into its subsurface. The suppression of CO adsorption on Pt single atoms stems from coordination saturation (18-electron rule) rather than the physical coverage of Pt atoms by the support. Based on the new finding it is revealed that single atoms are the true active sites in the hydrogenation of 3-nitrostyrene, while Pt NPs barely contribute to the activity since the NP sites are selectively encapsulated. The findings in this work provide a new approach to study the active sites by tuning SMSI.

Origin of CO2 as the main carbon source in syngas-to-methanol process over Cu: theoretical evidence from a combined DFT and microkinetic modeling study

A theoretical study combining DFT and microkinetic modeling provides evidence that CO₂ is the main carbon source in methanol synthesis from syngas (CO, CO₂ and H₂) over Cu.

Computational insights into the strain effect on the electrocatalytic reduction of CO2 to CO on Pd surfaces

Electrochemical CO2 reduction reaction (CO2RR) provides a promising scenario to achieve carbon renewable energy storage and alleviate energy depletion. It was found experimentally in the literature that strain over Pd surfaces can adjust the activity and selectivity of electrocatalytic CO2RR. Here, using density functional theory (DFT) calculations and the Sabatier analysis method, we investigated the electrochemical reduction of CO2 to CO at different electric potentials over Pd surfaces with lattice strains of -2%, -1%, 1% and 2%. Four types of Pd surfaces with different structures and co-ordination numbers were considered, namely Pd(111), (100), (110) and (211). We obtained the differential adsorption energy of key intermediates in CO2RR, i.e. COOH and CO, with DFT as a function of CO coverage on these Pd surfaces. Further analysis showed that the adsorption energy at high coverage might be correlated with the Coulomb interaction energy between surface species. With the adsorbate-adsorbate interactions included in the analyses, we found that the strained Pd(111) surface shows the highest CO2RR activity among the four surfaces considered, which is consistent with previous experimental observations. These results highlight the significance of surface strain effects on the reactivity of CO2RR and provide guidance for practical catalyst development.

Intrinsic effects of strain on low-index surfaces of platinum: roles of the five 5d orbitals

The inconsistent change in five 5d orbitals on strained Pt low-index induces abnormal species adsorption behaviours.

Intermetallic PdIn catalyst for CO2 hydrogenation to methanol: mechanistic studies with a combined DFT and microkinetic modeling method

Reaction pathways of methanol and carbon monoxide formation from CO₂ hydrogenation over PdIn(110) and (211) with a combined density functional theory and microkinetic modeling approach.