Phornphimon Maitarad

Enhanced catalytic performance of V2O5–WO3/Fe2O3/TiO2 microspheres for selective catalytic reduction of NO by NH3

The V2O5–WO3/Fe2O3/TiO2 microsphere catalysts were prepared by an impregnation method. The catalytic test results showed that the Fe2O3 additives in V2O5–WO3/Fe2O3/TiO2 improved the NO decomposition in the temperature range of 200–400 °C. The characterization results indicated that the iron oxides mainly existed in the form of Fe2O3, which was beneficial for the oxidation of NO to NO2. Meanwhile, the superior catalytic performance of V2O5–WO3/Fe2O3/TiO2 for the selective catalytic reduction of NO has been attributed to its highly dispersed active species, and lots of surface adsorbed oxygen. Prominently, the activity of V2O5–WO3/Fe2O3/TiO2 microspheres can be recovered after cutting off SO2, and thus these combination metal oxide catalysts show not only high catalytic activities but also good resistance to SO2.

Excited-State Geometries of Heteroaromatic Compounds: A Comparative TD-DFT and SAC-CI Study

The structures of low-lying singlet excited states of nine π-conjugated heteroaromatic compounds have been investigated by the symmetry-adapted cluster-configuration interaction (SAC-CI) method and the time-dependent density functional theory (TDDFT) using the PBE0 functional (TD-PBE0).In particular, the geometry relaxation in some ππ* and nπ* excited states of furan, pyrrole, pyridine, p-benzoquinone, uracil, adenine, 9,10-anthraquinone, coumarin, and 1,8-naphthalimide as well as the corresponding vertical transitions, including Rydberg excited states, have been analyzed in detail. The basis set and functional dependence of the results was also examined. The SAC-CI and TD-PBE0 calculations showed reasonable agreement in both transition energies and excited-state equilibrium structures for these heteroaromatic compounds.

Fe2O3 nanoparticles anchored in situ on carbon nanotubes via an ethanol-thermal strategy for the selective catalytic reduction of NO with NH3

Fe2O3 nanoparticles were anchored in situ on carbon nanotubes (CNTs) via an ethanol-thermal route, for the selective catalytic reduction (SCR) of NO with NH3. The structure and surface characteristics of the obtained catalysts were measured by transmission electron microscopy, X-ray diffraction, N2 adsorption–desorption isotherms, Raman, X-ray photoelectron spectroscopy, H2-temperature programmed reduction, and NH3-temperature programmed desorption. Compared with catalysts prepared via impregnation or co-precipitation methods, the synthesized catalyst showed better catalytic activity and a more extensive operating-temperature window. The TEM and XRD results suggested that the iron species was uniformly anchored on the surface of the CNTs. The Raman and XPS results indicated that the catalyst has a relatively higher number of defects, a higher atomic concentration of Fe present on the surface of the CNTs and a higher content of chemisorbed oxygen species. The H2-TPR and NH3-TPD results demonstrated that the catalyst possesses a more powerful reducibility and stronger acid strength than the other two catalysts. Based on the above-mentioned physicochemical properties, the obtained catalyst showed an excellent performance in the SCR of NO to N2 with NH3. Additionally, the catalyst also presented outstanding stability, H2O resistance and SO2 tolerance.

Metal–Porphyrin: A Potential Catalyst for Direct Decomposition of N2O by Theoretical Reaction Mechanism Investigation

The adsorption of nitrous oxide (N2O) on metal-porphyrins (metal: Ti, Cr, Fe, Co, Ni, Cu, or Zn) has been theoretically investigated using density functional theory with the M06L functional to explore their use as potential catalysts for the direct decomposition of N2O. Among these metal-porphyrins, Ti-porphyrin is the most active for N2O adsorption in the triplet ground state with the strongest adsorption energy (-13.32 kcal/mol). Ti-porphyrin was then assessed for the direct decomposition of N2O. For the overall reaction mechanism of three N2O molecules on Ti-porphyrin, two plausible catalytic cycles are proposed. Cycle 1 involves the consecutive decomposition of the first two N2O molecules, while cycle 2 is the decomposition of the third N2O molecule. For cycle 1, the activation energies of the first and second N2O decompositions are computed to be 3.77 and 49.99 kcal/mol, respectively. The activation energy for the third N2O decomposition in cycle 2 is 47.79 kcal/mol, which is slightly lower than that of the second activation energy of the first cycle. O2 molecules are released in cycles 1 and 2 as the products of the reaction, which requires endothermic energies of 102.96 and 3.63 kcal/mol, respectively. Therefore, the O2 desorption is mainly released in catalytic cycle 2 of a TiO3-porphyrin intermediate catalyst. In conclusion, regarding the O2 desorption step for the direct decomposition of N2O, the findings would be very useful to guide the search for potential N2O decomposition catalysts in new directions.

Mechanistic insight into the selective catalytic reduction of NO by NH3 over low-valent titanium-porphyrin: a DFT study

In this work, the reaction mechanism of ammonia selective catalytic reduction (NH3-SCR) of nitric oxide over a low-valance Ti-porphyrin catalyst was studied by density functional theory (DFT) calculations for both low- and high-spin states. The reaction proceeds via (i) NH3 complexation with the Ti-porphyrin complex, and its subsequent oxidation to NH2, with a large activation barrier of 32–34 kcal mol−1 because of the difficulty of N–H bond dissociation. (ii) Bonding between NO and the NH2 ligand forms an NH2NO intermediate by an Eley–Rideal-type mechanism. The calculated activation energies for this step are 4.34 and 10.22 kcal mol−1 for the low- and high-spin states, respectively. (iii) Formation of NHNOH by rearrangement of the NH2NO intermediate. Spin crossings in steps (ii) and (iii) play an important role in the overall reaction by providing a mechanism with a smaller activation energy of 17.05 kcal mol−1, compared with 28.02 kcal mol−1 for the un-catalyzed reaction. (iv) In the final step, the decomposition of NHNOH results in the formation of N2 and H2O molecules, with a small energy barrier of approximately 7–9 kcal mol−1. For pairwise pathway comparisons, Ti-porphyrin in the triplet state offers 8.43 kcal mol−1 greater stability than the singlet does, and the reaction is more likely to proceed through a high-spin pathway because of its lower relative energies compared to the low spin. The obtained activation energies for NH3-SCR of NO are comparable with theoretical results for the reduction of NO over V2O5 and Fe-zeolite systems. Thus, Ti-porphyrin has potential as an alternative catalyst for NH3-SCR of nitric oxide.

Particular interaction between pyrimethamine derivatives and quadruple mutant type dihydrofolate reductase of Plasmodium falciparum: CoMFA and quantum chemical calculations studies.

Comparative molecular field analysis (CoMFA) was performed on twenty-three pyrimethamine (pyr) derivatives active against quadruple mutant type (Asn51Ile, Cys59Arg, Ser108Asn, Ile164Leu) dihydrofolate reductase of Plasmodium falcipaarum (PfDHFR). The represented CoMFA models were evaluated based on the various three different probe atoms, Csp3 (+1), Osp3 ( − 1) and H (+1), resulting in the best model with combined three types of probe atoms. The statistical results were = 0.702, Spress = 0.608, = 0.980, s = 0.156, and = 0.698 which can explain steric contribution of about 50%. In addition, an understanding of particular interaction energy between inhibitor and surrounding residues in the binding pocket was performed by using MP2/6-31G(d,p) quantum chemical calculations. The obtained results clearly demonstrate that Asn108 is the cause of pyr resistance with the highest repulsive interaction energy. Therefore, CoMFA and particular interaction energy analyses can be useful for identifying the structural features of potent pyr derivatives active against quadruple mutant type PfDHFR.

The complete reaction mechanism of H2S desulfurization on an anatase TiO2 (001) surface: a density functional theory investigation

The complete reaction mechanism of H2S desulfurization on anatase TiO2 (001) surface was elucidated using the plane-wave based density functional theory (DFT) method. The reaction starts from the dissociative adsorption of H2S on the TiO2 surface. Subsequently, two competitive routes, H2O and H2 formation, were investigated. The activation barriers for H2O formation range from 11 to 13 kcal mol−1, whereas those for H2 formation are extremely high in the range of 67–87 kcal mol−1. On the basis of the activation energy barriers, the results indicate that the anatase TiO2 (001) is very active for H2S desulfurization to produce H2O, resulting in S-substitution at the O2c sites on the TiO2 (001) surface. Electronic charge analyses indicate that S-doping onto the TiO2 surface can enhance the photocatalytic activity of TiO2 by reducing its band gap. In addition, by comparison with other metal oxide catalysts, such as TiO2 (101), CeO2 (111), CeO2 (101), ZnO (1010) and α-Fe2O3 (0001), we found that TiO2 (001) is the most promising catalyst for H2S desulfurization.

Mn–Fe bi-metal oxides in situ created on metal wire mesh as monolith catalysts for selective catalytic reduction of NO with NH3

In this work, we use an Fe wire mesh to provide homogeneous nucleation sites to support a continuous in situ growth of Mn–Fe bi-metal oxides as monolith catalysts for selective catalytic reduction of NO with NH3. The strategy of a “twin iron source” makes the Mn–Fe seeds easily grow on the Fe wire mesh through the surface Fe metal sites rather than free growth. The Fe wire mesh exhibited excellent affinity properties with Mn–Fe hydroxides precursor. Through the calcination treatment, a spinel structure of Mn–Fe bi-metal oxides coated monolithic catalyst was prepared and used for denitrification. By adjusting the ratio of the Mn–Fe precursors, we obtained Mn–Fe bi-metal oxides with various morphologies coated on the surface of Fe wire mesh. Impressively, the cube-like Mn–Fe bi-metal oxides structure on the Fe wire mesh as monolith catalysts exhibited high De-NOx performance, catalytic activity, stability, H2O tolerance, K+ poisoning resistance and regeneration performance. The results showed that the spinel structure of Mn–Fe bi-metal oxides in the coating layer was the critical factor for enhanced adsorption behaviours and reducibilities, which promoted selective catalytic reduction of NO with NH3. The good adhesion between the Mn–Fe spinel and Fe wire mesh contributed to the super stability and the strong adsorption properties of NH3, which made it dominant in the NH3 adsorption process competing with water. The obtained monolith catalysts showed good resistances to K+ poisoning and good regeneration performance, which can be attributed to the structural stability of Mn–Fe spinel and strong synergistic effect between the support and active species. This new kind of monolithic catalyst prepared by an in situ technique can be used as a potential substitute for vanadium based ceramic catalysts.

Improved NOx reduction in the presence of alkali metals by using hollandite Mn–Ti oxide promoted Cu-SAPO-34 catalysts

Improved NOx reduction in the presence of alkali metals is still challenging. In this work, we developed novel hollandite Mn–Ti oxide promoted Cu-SAPO-34 catalysts (HMT@Cu–S) for the selective catalytic reduction (SCR) of NOx with NH3via the isolation of active sites and alkali metal trapping sites. The HMT@Cu–S catalysts exhibited excellent SCR activity and N2 selectivity. More importantly, the HMT@Cu–S catalysts had stronger resistance against alkali metal poisoning compared to Cu-SAPO-34 catalysts. It was found that these newly developed catalysts had superior alkali metal resistance compared to the reported catalysts, making them attractive for environmental application. The hollandite Mn–Ti oxides acted as a protective layer to trap alkali metal ions according to an ion exchange mechanism. From in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) studies of desorption, it could be concluded that after alkali metal poisoning, the NH3 species of the HMT@Cu–S catalysts were more unstable; therefore, they could easily participate in the SCR reactions. Additionally, the NOx species showed no change after introduction of alkali metal ions due to alkali metal trapping effects. Moreover, the in situ DRIFTS of transient reactions indicated that the NH3 species were much more easily adsorbed on K-HMT@Cu–S catalysts and that the formed NH3 species that were unaffected by alkali metal ions were highly reactive. The present investigations provide an effective strategy for the design and the application of catalysts with outstanding catalytic activity and alkali metal resistance.

An Experimental and Theoretical Study on the Aldol Condensation on Zirconium-Based Metal-Organic Framework

The aldol condensation of acetone in zirconium-based metal-organic framework functionalized by a sulfonic acid group (UiO-66-SO3H) has been theoretically investigated using the density functional theory. Acetone adsorbed on the UiO-66-SO3H with the adsorption energy of -17.4 kcal/mol. The catalyzed reaction has been proposed to be a two-step mechanism: the tautomerization of keto form to produce enol form of acetone, and the aldol condensation to produce diacetone alcohol. The activation energies were calculated to be 27.2 and 6.4 kcal/mol, respectively. For the experimental part, UiO-66-SO3H catalyst was synthesized and characterized by X-ray diffraction and IR spectroscopy. The catalytic reaction was carried out in a stirred batch reactor at different temperatures to optimize the reaction conditions. The obtained products were analyzed by 1H-NMR spectroscopy and chromatography techniques. This study demonstrated that UiO-66-SO3H can be used as a solid catalyst for the aldol condensation reaction.