A Rapid Access to Novel and Known Benzimidazole Derivatives Using Silica Chloride as a Reusable Catalyst

A new application of silica chloride as an easily available and reusable solid acid catalyst for the synthesis of benzimidazole and its derivatives through the condensation of o‐phenylenediamines and orthoesters under thermal and solvent‐free conditions is described. This novel and eco‐friendly method is very cheap and has many advantages including excellent yields, short reaction time, and simple work‐up procedure.     

Quantum-chemical calculations on graphitic carbon nitride (g-C3N4) single-layer nanostructures: polymeric slab vs. quantum dot

Graphitic carbon nitride (g-C₃N₄) has been the focus of enormous attention in recent years for its fantastic in-plane and surface properties. Several periodic and cluster models of g-C₃N₄ including a quantum dot have been investigated using density functional theory (DFT) at the HSE06/Def2-TZVP level. The quantum dot with side triazine rings in nearly perpendicular alignment to the central ring was (by 98.40 kcal/mol) more stable than any other cluster, including its planar analogue—a metastable phase of carbon nitride. The g-C₃N₄ quantum dot showed the largest deviation (3.27 eV, 7.9%) from the bandgap of the polymeric material. On the other hand, the unrelaxed symmetrical cluster had the smallest deviation (+?0.03 eV, 1.0%) from the reference bandgap (and also in terms of global hardness), indicating that it could be taken as a replacement cluster for modeling of a polymeric surface in such explorations. The plots of the density of states (DOS) revealed the inherent instabilities of the planar models compared to the quantum dot. Furthermore, the g-C₃N₄ quantum dot showed the highest chemical hardness among the models investigated. The electronic band structures of the g-C₃N₄ quantum dot implied its relatively better photoabsorption ability referenced to the polymeric surface. However, the structural changes had significant effects on the orbital and charge distributions in the C₃N₄ models.

     

Effect of promoter on selective hydrogenation of furfural over Cu-Cr/TiO2 catalyst

The selective hydrogenation of furfural has been investigated over the titania-supported monometallic (Cu) and bimetallic (Cu–Cr) catalysts. The catalytic performances were assessed over 4 h of run length under atmospheric pressure at the hydrogen-to-hydrocarbon ratio of 10.6 and 453 K. The results represented that the level of furfural conversion over the non-promoted catalyst was very low (below 10%) while the promoted one showed considerable furfural conversion during this period (higher than 70%). However, both catalysts exhibited high durability and selectivity towards furfuryl alcohol.

     

Ethene Protonation Over Silica-Grafted Metal (Cr,Mo, and W) Oxide Catalysts: A Comparative Nanocluster Modeling Study

Fundamental insights into the ethene protonation reaction was obtained over different cluster models of acidic CrO_x/SiO₂, MoO_x/SiO₂, and WO_x/SiO₂ catalysts at the M06/Def2-TZVP level of theory. The clusters varied from MSiO₄H₃ structures (all-fixed, H-optimized, and all-relaxed) to MSi₄O₄H₉ (saturated with H atoms) and further to MSi₄O₁₃H₉ (saturated with OH atoms). The formation of the ethene protonation adducts followed the order of WO_x/SiO₂ < MoO_x/SiO₂ < CrO_x/SiO₂ in terms of the thermodynamic favorability which agreed well with the partial charges and the global softness data. The natural bond orbital analysis revealed a partial flow of electrons from the bridging O atom to the hydrocarbon fragment than to the metal during the initiation. Although the interbond angles were comparably different in the largest cluster, the bond lengths and orbital energy levels did not change significantly from a cluster to another. Concerning the thermochemical properties, any of the cluster models would be utilized within a 2 kcal/mol confidence limit.     

Structural diversity of metallacycle intermediates for ethylene dimerization on heterogeneous NiMCM-41 catalyst: a quantum chemical perspective

Structural Chemistry - Nanocluster models were investigated to explore the diversity of metallacycle intermediates for ethylene dimerization over NiMCM-41 at B3LYP/6-311+G* and M06/Def2-TZVP. The...     

Characterization of extraframework Zn<Superscript>2+</Superscript> cationic sites in silicalite-2: a computational study

Siting and coordination of Zn²⁺ ions at six plausible positions in all-silicate ZSM-11 material known as silicalite-2 have been investigated via hybrid density functional theory method at the B3LYP level employing molecular cluster models to represent the active site. The symmetrical trapping of Zn²⁺ ions in six-membered ring (6MR) sites of the main channels with a fivefold coordination to the framework oxygens was associated with the most stable binding among the investigated sites. On the contrary, the cation was found to be most weakly bound in sites at the intersections where it was twofold coordinated with slightly shorter Zn–O distances. A basket-like position for Zn doping was also recognized that exhibited no clear trends in the electronic and structural properties investigated.     

Adsorption of toxic mercury,lead, cadmium,and arsenic ions on black phosphorous nanosheet: first-principles calculations

Structural Chemistry - The applicability of the black phosphorus monolayer (BPML) material to remove cadmium, lead, mercury, and arsenic ions from contaminated environments was evaluated. The...     

Highly improved carbon dioxide sensitivity and selectivity of black phosphorene sensor by vacancy doping: A quantum chemical perspective

The adsorption and sensing properties of a carbon dioxide (CO₂) molecule on the pristine (BP) and vacancy-doped (DP) black phosphorusmono layers have been investigated using the periodic density functional theory at Heyd-Scuseria-Ernzerhof (HSE06)/triple-zeta valence polarization (TZVP). For both sensors, the most stable structures among the recognized possibilities preferred a linear configuration for carbon dioxide, with a shorter equilibrium distance (2.13 Å) on the defect-containing surface. Although carbon dioxide was weakly physiosorbed on both phosphorene sensors (up to −2.52 kcal/mol), the defect-engineered material presented highly improved sensitivity (by a factor of 6.6) to CO₂ compared to the pristine layer. The former was also a (2.6 times) better work function sensor of carbon dioxide. At the same time, recovery was extremely fast (lasting for 70 ps at most) at room temperature. The selectivity coefficient of carbon dioxide was also strikingly high (64.0). The improved nanosensor would be a step forward in the rational design of highly sensitive and reusable detectors of carbon dioxide.