Distinctions between Supported Au and Pt Catalysts for CO Oxidation: Insights from DFT Study

Distinctions between supported Au and Pt catalysts on TiO₂(110) for CO oxidation have been investigated by means of density functional theory calculations. Our study shows that the following factors determine the obvious differences between two kinds of catalysts for CO oxidation: (1) The adsorption strength of Au₁₁ is much weaker than that of Pt₁₁ on TiO₂(110), but both are strongly dependent on the surface properties of TiO₂. The addition of Pt increases the interaction between the alloyed cluster and TiO₂ support. (2) O₂ can adsorb only on the interfacial site between Au and TiO₂(110), whereas O₂ can adsorb on both the interfacial and metal sites of supported Pt nanoparticles. (3) CO is directly activated by the adsorbed molecular oxygen on the interfacial site of Au₁₁/TiO₂(110)<i>_OH</i>. While on Pt₁₁/TiO₂(110)<i>_OH</i>, the main reaction pathway is the dissociated oxygen reacting with CO. Once a Pt ensemble is formed on Au clusters (such as Au₈Pt₃/TiO₂(110)<i>_OH</i>), both of the reaction mechanisms work

First-Principles Thermodynamics Study of Spinel MgAl₂O₄ Surface Stability

The surface stability of all possible terminations for three low-index (100, 110, 111) structures of spinel MgAl₂O₄ was studied using a first-principles-based thermodynamic approach. The surface Gibbs free energy results indicate that the 100_AlO₂ termination is the most stable surface structure under ultrahigh vacuum at <i>T</i> = 1100 K regardless of an Al-poor or Al-rich condition. With increasing oxygen pressure, the 111_O₂(Al) termination becomes the most stable surface in the Al-rich condition. The oxygen vacancy formation is thermodynamically favorable over the 100_AlO₂, 111_O₂(Al), and (111) structures with Mg/O connected terminations. On the basis of the surface Gibbs free energies for both perfect and defective surface terminations, 100_AlO₂ and 111_O₂(Al) are the most dominant surfaces in Al-rich conditions under atmospheric conditions. This is also consistent with our previously reported experimental observation

Promotional Effects of Cesium Promoter on Higher Alcohol Synthesis from Syngas over Cesium-Promoted Cu/ZnO/Al₂O₃ Catalysts

The promotional effects of a cesium promoter on higher alcohol (C₂₊OH) synthesis from syngas over Cs₂O-Cu/ZnO/Al₂O₃ catalysts were investigated using a combined experimental and density functional theory (DFT) calculation method. In the presence of a cesium promoter, the C₂₊OH productivity increases from 77.1 to 157.3 g kg_cat^–1 h^–1 at 583 K due to the enhancement of the initial C–C bond formation. A detailed analysis of chain growth probabilities (CGPs) confirms that initial C–C bond formation is the rate-determining step in the temperature range of 543–583 K. Addition of a cesium promoter significantly increases the productivities of 2-methyl-1-propanol, while the CGP values (C₃* to 2-methyl-C₃*) are almost unaffected. With the assistance of a cesium promoter, the CGPs of the initial C–C bond formation step (C₁* to C₂*) increase from 0.13 to 0.25 at 583 K. DFT calculations indicate that the initial C–C bond formation during syngas synthesis over the ZnCu(211) model surface is mainly due to the HCO + HCO coupling. In the presence of Cs₂O, the stabilities of key intermediates such as HCO and H₂CO are enhanced, which facilitates both HCO + HCO and HCO + H₂CO coupling steps with lower activation barriers. In addition, Bader charge analysis suggests that the presence of cesium ions could facilitate nucleophilic coupling between HCO and H₂CO for the initial C–C bond formation

Strong Sulfur Binding with Conducting Magnéli-Phase Ti_<i>n</i>O_{2<i>n</i>–1} Nanomaterials for Improving Lithium–Sulfur Batteries

Lithium–sulfur batteries show fascinating potential for advanced energy storage systems due to their high specific capacity, low-cost, and environmental benignity. However, the shuttle effect and the uncontrollable deposition of lithium sulfide species result in poor cycling performance and low Coulombic efficiency. Despite the recent success in trapping soluble polysulfides via porous matrix and chemical binding, the important mechanism of such controllable deposition of sulfur species has not been well understood. Herein, we discovered that conductive Magnéli phase Ti₄O₇ is highly effective matrix to bind with sulfur species. Compared with the TiO₂–S, the Ti₄O₇–S cathodes exhibit higher reversible capacity and improved cycling performance. It delivers high specific capacities at various C-rates (1342, 1044, and 623 mAh g^–1 at 0.02, 0.1, and 0.5 C, respectively) and remarkable capacity retention of 99% (100 cycles at 0.1 C). The superior properties of Ti₄O₇–S are attributed to the strong adsorption of sulfur species on the low-coordinated Ti sites of Ti₄O₇ as revealed by density functional theory calculations and confirmed through experimental characterizations. Our study demonstrates the importance of surface coordination environment for strongly influencing the S-species binding. These findings can be also applicable to numerous other metal oxide materials