Density Functional Theory Investigation for Catalytic Mechanism of Gasoline Alkylation Desulfurization over NKC‑9 Ion-Exchange Resin

The molecular level understanding of the mechanism about the 3-methylthiophene (3MT) alkylation with isobutylene (IB) as well as the side reaction of IB dimerization over NKC-9 cation exchange resin has been investigated using the density functional theory (DFT) of quantum chemical method. A model of benzene sulfonic acid was used to represent the cation-exchange resin catalyst. Two different reaction mechanism typesstepwise scheme and concerted scheme have been evaluated. Activation energies of each reaction path which were obtained from the DFT results have been improved by single-point MP2 calculations. In the stepwise mechanism, both 3MT alkylation and IB dimerization proceed by adsorption and protonation of the IB to form a sulfonic ester intermediate, and then by C–C bond formation between the sulfonic ester intermediate and another 3MT or IB to give the reaction products. The second step is rate-determining and has activation barriers of 148.41 kJ/mol for 3MT alkylation and 160.52 kJ/mol for IB dimerization. In the concerted mechanism, the reaction occurs in one step of simultaneous protonation and C–C bond formation. The activation barrier is calculated to be 169.10 kJ/mol for 3MT alkylation, and that for IB dimerization is 174.02 kJ/mol. The results revealed that the reaction mechanism of 3MT alkylation was very similar to that of IB dimerization, and the stepwise mechanism dominated both the 3MT alkylation and IB dimerization. Moreover, 3MT alkylation is more easily occurs than IB dimerization during gasoline alkylation desulfurization

Design, Synthesis, and Analysis of Thermophysical Properties for Imidazolium-Based Geminal Dicationic Ionic Liquids

To enhance the thermal stability of ionic liquids (ILs) and increase the latent heat, the effect of amount of hydrogen bonds for geminal dicationic ionic liquids (DILs) was investigated and compared to that of monocationic analogues. A series of geminal dicationic ionic liquids with alkyl chain or electronegativity functional groups in the imidazolium were synthesized. Thermal stability was determined by TGA; melting point, heat of fusion, and heat capacity were investigated by DSC for synthetic DILs. The effect of molecular structure on the heat of fusion was examined by changes alkyl side-chain, linkage chain, C2–H of imidazole ring, and functional groups. Hydrogen bonding in DILs was studied, in the case of C₂(eim)₂(Br)₂, by single-crystal X-ray diffraction. The thermal analysis results indicate that functionalized geminal dicationic ionic liquids show excellent thermal stability. The decomposition temperatures of geminal dicationic ionic liquids can be up to 603.74 K, and the latent heat can reach 159.35 J g^–1. It is increased on average by 64.5% and 212.5%, respectively, as compared to alkyl chain ionic liquid (C₄mim)­Br. It can be expected that these geminal dicationic ionic liquids are suitable for thermal storage applications

Synthesis and characterization of <i>trans</i>-di(nitrobenzo)- and di(aminobenzo)-18-crown-6 derivatives with high selectivity

<p>The dibenzo-18-crown-6 derivatives such as di(nitrobenzo)-18-crown-6 and di(aminobenzo)-18-crown-6 were synthesized by nitration reaction and catalytic hydrogenation with high selectivity. The chemical structures were determined by FTIR, ¹H NMR, ¹³C NMR, and UV. Regarding the mixture of Ac₂O and HNO₃ as nitrating agent, the reaction exhibited commendable <i>trans</i>-isomer selectivity. Effects of nitrating agent ratio, reaction temperature and reaction time on yield of <i>trans</i>-di(nitrobenzo)-18-crown-6 were investigated. The yield of <i>trans</i>-di(nitrobenzo)-18-crown-6 was 62.9% for nitrating agent ratio of 1/1, reaction temperature of 50 °C and reaction time of 5 h. Moreover, effect of reaction time on <i>trans</i>-di(aminobenzo)-18-crown-6 was also studied.</p

Synthesis and Characterization of Functionalized Ionic Liquids for Thermal Storage

A series of imidazolium-based ionic liquids were synthesized by introducing functional groups in the imidazolium cation to develop new phase change materials. The structures of these ionic liquids were determined by nuclear magnetic resonance; the quantum calculation was performed based on density functional theory by Gaussian 09 to determine the number of hydrogen bonds among the ions. The heat of fusion, heat capacity, and thermal storage density of the ionic liquids were investigated by DSC; in addition, the thermal stability was determined by TGA. The thermal analysis results indicate that new functionalized ionic liquids have excellent thermal stability with decomposition temperatures higher than 475 K. In addition, the heat of fusion, heat capacity, and thermal storage density of the functionalized ionic liquids increased on average by 34, 86.5, and 100%, respectively, compared with alkyl chain ionic liquids with the same carbon numbers. These superior properties are attributed to the additional hydrogen bonds in the functionalized ionic liquids

NiSx Quantum Dots Accelerate Electron Transfer in Cd_0.8Zn_0.2S Photocatalytic System via an rGO Nanosheet “Bridge” toward Visible-Light-Driven Hydrogen Evolution

Minimizing the charge transfer barrier to realize fast spatial separation of photoexcited electron–hole pairs is of crucial importance for strongly enhancing the photocatalytic H₂ generation activity of photocatalysts. Herein, we propose an electron transfer strategy by reasonable design and fabrication of high-density NiSx quantum dots (QDs) as a highly efficient cocatalyst on the surface of Cd_0.8Zn_0.2S/rGO nanosheet composites. Under visible-light irradiation, the formation of a two-dimensional (2D) Cd_0.8Zn_0.2S/rGO nanohybrid system with 2 wt % NiSx loading gave a prominent apparent quantum efficiency (QE) of 20.88% (435 nm) and H₂ evolution rate of 7.84 mmol g^–1 h^–1, which is 1.4 times higher than that of Pt/Cd_0.8Zn_0.2S/rGO. It is believe that the introduced rGO nanosheets and NiSx QDs obviously improved the interfacial conductivity and altered the spatial distribution of electrons in this nanoarchitecture. Thus, the synergistic effects of interfacial junctions result in a regulated electron transportation pathway along the basal planes and ultrafast transfer and spatial separation of photoexcited carriers, which are responsible for the enhanced photocatalytic performance. This work gives a facile and effective strategy to understand and realize rationally designed advanced photocatalysts for high-efficiency, stable, and cost-efficient solar hydrogen evolution applications

Chemical Looping Reforming of Toluene as Volatile Model Compound over LaFe_<i>x</i>M_1–<i>x</i>O₃@SBA via Encapsulation Strategy

Aiming at the problems of large tar influence and low gasification efficiency in traditional biomass gasification, in this paper, a chemical looping reforming (CLR) of volatiles from biomass pyrolysis based on decoupling strategy is proposed to convert macromolecular volatiles into hydrogen-rich syngas. A series of highly active and selective oxygen carrier (OC) SBA-15 encapsulating LaFexM1–xO3 (M = Ni, Cu, Co) for the biomass CLR process was developed. Reaction kinetics and cycling performance of toluene CLR process on LaFe0.6Co0.4O3@SBA-15 OCs were explored. Experimental results showed that the encapsulation effect gave the metal oxide a better dispersion, reduced the sintering, and improved the reaction performance. Compared with LaFeO3, the toluene conversion increased from 52.3% to 79.7%, the CO selectivity improved from 57.0% to 87.4%, and the oxygen release (OR) increased by 100% after encapsulation in SBA-15. Due to the substitution of Ni2+, Cu2+ and Co2+ on Fe3+, more oxygen vacancies in OCs were created, and both conversions of toluene and selectivity of CO were improved. Among them, the incorporation of Co had the best performance, the toluene conversion was 81.6%, and the CO selectivity was 96.8%. The kinetics of the LaFe0.6Co0.4O3@SBA-15 reaction was solved using a gas–solid reaction model with an activation energy of 103.9 kJ mol–1 and a pre-exponential factor of 123.8 s–1. The performance of LaFe0.6Co0.4O3@SBA-15 was tested for 10 cycles, and it was found that conversion of toluene and CO selectivity were well-maintained at 90.0%–92.0% and 93.0%–96.0%, respectively. This study could guide the selection of OCs in reforming macromolecular volatiles from biomass pyrolysis to produce hydrogen-rich syngas

Tailoring Catalytic and Oxygen Release Capability in LaFe_1–<i>x</i>Ni_<i>x</i>O₃ to Intensify Chemical Looping Reactions at Medium Temperatures

Perovskite oxygen carriers in a methane chemical looping partial oxidation process enable high reactivity over 850 °C. Lowering the reaction temperature helps to circumvent energy dissipation and couple the above-mentioned process with energy-efficient systems. This paper demonstrates the attractive oxygen-donating capacity of Fe–Ni-based perovskite oxygen carriers for methane partial oxidation. The aforesaid process exhibits more than 70% methane conversion and 6.71 mmol·g–1 unit syngas yield at 700 °C, using LaFe0.5Ni0.5O3. This impressive high reactivity mainly originates from the lowered lattice oxygen bonding strength and the spontaneously constructed active Ni-rich surface of perovskite oxides by Ni doping. In addition to the outward migration of lattice oxygen, active metal elements, such as Ni, continuously segregate to the surface with the reduction of perovskite oxides, promoting methane partial oxidation. We speculate that the chemical looping reaction pathway consists of consecutive competitive reactions based on analysis of the real-time product distribution and the dynamic evolution of oxygen carriers. Highly selective syngas production can be achieved on LaFe0.5Ni0.5O3 by reducing reaction temperatures or increasing space velocity to balance methane dissociation and lattice oxygen release kinetics. Irreversible Ni segregation and phase-separation-induced inert La2O3 on the surface of perovskite oxides during redox cycles are responsible for the cyclic performance degradation of oxygen carriers. This work offers intriguing references to design perovskite oxygen carriers for intensifying the medium-temperature chemical looping partial oxidation process