Search

[Display omitted] • MOFs-derived Ni-Co alloy catalysts were used in NCH selective hydrogenation. • Ni-Co alloy effects facilitate CoO x reduction and increase the Co0 amounts. • Ethylenediamine favors the N -CHH formation and reduces the whole energy barriers. • Pyridinic-N favors intermediate N -CHH conversion to CHO. • Ni 1 Co 2 (1 1 1) crystal surface presents the lowest energy barrier of the α-H transfer. High-efficiency Ni-Co alloy encapsulated in N -doped carbon layer (Ni 1 Co 2 @NC-APTES) catalysts were prepared via simple Ni-Co-MOF pyrolyzation and applied in the selective hydrogenation of nitrocyclohexane (NCH) to cyclohexanone oxime (CHO). The results show that the alloy effects between Ni and Co can highly promote catalytic activity. The appropriate Ni addition can facilitate the reduction of CoO x and increase zero-valent Co (Co0) amounts. Moreover, pyridinic-N doping increases the Lewis basicity, which favors the intermediate cyclohexylhydroxylamine (N -CHH) conversion to CHO. Additionally, the in-situ DRIFT and density functional theory (DFT) calculations propose the mechanism for NCH hydrogenation in ethylenediamine (EDA) and the results show that the EDA changes the reaction path of NCH hydrogenation to CHO, prefers to form N -CHH, and significantly reduces the whole reaction energy barrier of NCH to CHO. Moreover, the Ni 1 Co 2 (1 1 1) crystal surface with the lowest d -band center and the strongest Ni-Co alloy effects presents the highest adsorption energies of H 2 and NCH, the lowest adsorption energies of H* and CHO, and the lowest energy barrier of the α -H transfer which is conducive to form the N -CHH. Under the optimum conditions, the Ni 1 Co 2 @NC-APTES gives 93.6% selectivity to CHO at 94.5% NCH conversion in EDA. [ABSTRACT FROM AUTHOR]

Abstract: In this work, hydrophilic property of Ru (0001) with and without H adatoms was theoretically studied to increase the understanding of the partial hydrogenation of benzene to cyclohexene over ruthenium catalysts. Density functional theory based calculations suggest that formation of hydrogen bonding among the adsorbed H2O molecules results in a weakened interaction between the water adlayer and Ru (0001), while the calculated heat of adsorption containing the contribution of hydrogen bonding is no longer suitable for evaluating the hydrophilic property of the metal surface. The presence of H adatoms exerts an electrostatic repulsion on the adsorbed H2O molecules; thereby the latter can be in the state of chemisorption or physisorption on the Ru metal depending on the number of immediately adjacent H adatoms and on the relative distance to the H adatoms. By tuning the coverage of H adatoms, the surface hydrophilic/hydrophobic balance of the Ru metal can be effectively adjusted, which provides an approach to improve the selectivity to cyclohexene in the partial hydrogenation of benzene. [Copyright &y& Elsevier]

Abstract: From the adsorption point of view, partial hydrogenation of benzene to cyclohexene over the metallic Zn modified Ru-based catalyst was experimentally and theoretically investigated. A decreased hydrogenation activity but increased selectivity to cyclohexene over the prepared Ru-Zn/ZrO2 catalyst was observed in the partial hydrogenation of benzene. Theoretical calculations suggest that the above phenomena are mainly resulted from the depression of the chemisorption of benzene and cyclohexene on the modified catalyst, especially for the latter. Undesired deep hydrogenation from cyclohexene to cyclohexane in the middle and late reaction stage therefore is effectively retarded, by which an improved cyclohexene yield is guaranteed. An optimal Zn content of 2.72wt.% in the Ru-based catalyst was proposed by both the experiment and calculation for the partial hydrogenation of benzene, and a cyclohexene yield up to 44% was obtained over Ru-Zn/ZrO2 catalyst. [Copyright &y& Elsevier]

Abstract: In this work, the hydrogenation of cyclohexene over Ru–Zn/Ru(0001) surface alloy was investigated by a DFT study so as to improve the understanding of the catalytic mechanism of the partial hydrogenation of benzene to cyclohexene over Ru–Zn alloy catalyst. Calculation results show that the presence of Zn atoms on the surface alloy results in not only a direct decrease in sites for the chemisorption of cyclohexene but also a depressed adsorption capability of the neighboring surface Ru sites. For an adsorbed cyclohexene molecule, whether the subsequent hydrogenation can be readily performed actually is determined by the relative position among the Zn atom, the H atom, and the adsorbed cyclohexene molecule. In most cases, the hydrogenation is forbidden because of the repulsion from Zn atoms to the nearby H atoms. Only in the specific situations in which the H atom participating in the reaction is not immediately close to the Zn atom, can the hydrogenation be accomplished with a relatively lower activation energy compared with the reactions on the Ru(0001) surface. From the perspectives of adsorption and reaction kinetics, Ru-based catalyst modified by metallic Zn is no longer suitable for the hydrogenation of cyclohexene, which is supposed to be crucial to the improvement of cyclohexene yield in the partial hydrogenation of benzene over Ru–Zn alloy catalyst. [Copyright &y& Elsevier]

Abstract: In this work, the denitrogenation of hydrocarbons under supercritical water oxidation environment was investigated in a rotated bomb reactor at 623–723K and 25–35MPa over sulfided NiMo catalyst. Quinoline was used as a model nitrogen-containing compound. A high reduction of total nitrogen up to about 85% was obtained. The denitrogenation pathway is composed of two consecutive steps: in situ H2 generation and the hydrogenation of quinoline. The hydrogenation mechanism of quinoline varies with reaction temperature because of the participation of supercritical water in HDN step. The strong adsorption of quinoline and its hydrogenation intermediates on catalyst surface has an adverse influence on total nitrogen reduction rate. [Copyright &y& Elsevier]

[Display omitted] • Ni 2 P/Al 2 O 3 with small nanoparticles and pure phase was controllably synthesized. • Ni 2 P/Al 2 O 3 shows excellent hydrogenation and desulfurization activities. • Nanoflower-like structure improves dispersion and accessibility of active sites. • The outstanding performance can be attributed to the rich Niδ+ active sites. The hydrogenation of unsaturated bonds and elimination of sulfur impurities in C 9 petroleum resin (C 9 PR) are crucial for improving its quality and performance. In this study, we prepared a nanoflower-like Ni 2 P/Al 2 O 3 catalyst using an in-situ synthesis combined with liquid-phase phosphidation strategy and applied for the production of value-added hydrogenated C 9 PR. In-situ synthesis of Ni-Al hydrotalcite anchors and disperses Ni nanoparticles, while liquid-phase phosphidation introduces high-content Niδ+ and Pδ− active sites and prevents the formation of inactive AlPO 4 , synergistically enhancing both hydrogenation and desulfurization activities. The synthesized Ni 2 P/Al 2 O 3 catalyst achieves a 99.6 % hydrogenation degree and reduces sulfur content from 137 ppm to 0 ppm, much better than the catalysts prepared by conventional impregnation and metal phosphate reduction methods. These results give valuable insights for designing efficient catalysts and advancing single-step hydrorefining processes to generate high-quality, value-added hydrogenated petroleum resins. [ABSTRACT FROM AUTHOR]

[Display omitted] • A series of Pd/SiO 2 catalysts with graded pore sizes were successfully prepared. • Macroporous catalysts facilitate NBR diffusion and improve metal utilization. • The correlation between D cat /D NBR with HD and Weisz modulus Φ were revealed. • Pd/N-SiO 2 -70 shows excellent activity (96.7%) and selectivity (100 %) to C = C. Pore diffusion effect plays a crucial role in heterogeneous hydrogenation of unsaturated polymers. However, how large pore size can eliminate the pore diffusion limitation remains a controversial issue. Herein, we prepared a series of Pd/SiO 2 catalysts with graded pore sizes and investigated the effect of pore size on hydrogenation activity of nitrile butadiene rubber (NBR). It is found that when the catalyst pore size (D cat) is 7 times of the diameter of NBR chains (D NBR), the Weisz modulus Φ can be reduced to < 0.3 thus the internal mass transfer limitation can be eliminated, making NBR easier to approach the active sites. Consequently, the catalysts with the D cat /D NBR > 7 exhibit excellent catalytic activity (96.7%) and selectivity (100%) to C = C. This work emphasizes that the pore size of catalysts can regulate the pore transfer limitation and the accessibility of internal active sites, providing useful guidance for the design of efficient macromolecular hydrogenation catalysts. [ABSTRACT FROM AUTHOR]

Supported Pd catalyst with an enhanced catalytic performance for polystyrene hydrogenation was successfully prepared by using macroporous silica microspheres (MSM) as the support. In order to eliminate the macromolecular diffusion limitation and improve the metal utilization, MSM was treated with steam at 800 °C first to remove mesopores and then refluxed with aqueous solutions to increase Si OH groups on the surface for Pd immobilization. The optimum support was obtained after the steam treatment for 2 h and using ammonia solution as reflux liquors, and the corresponding catalyst showed superior hydrogenation activity with a high conversion of 95%. [ABSTRACT FROM AUTHOR]

[Display omitted] • The flower-like nickel phosphide catalysts were prepared by a hydrotalcite strategy. • Ni 2 P/Al 2 O 3 catalyst showed excellent catalytic activity and desulfurization ability. • The outstanding performance ascribed to the rich active Niδ+ species. • The enhanced stability was due to strong interaction between active sites and support. The catalytic hydrogenation of petroleum resin (PR) to high value-added hydrogenated PR (HPR) represents a forward-looking technology for upgrading the pyrolysis petroleum by-product. Herein, flower-like and pure-phase supported nickel phosphide catalysts were controllably fabricated through a hydrotalcite strategy with red phosphorous as the P source. The PR hydrogenation activity of the catalysts followed the order of Ni 2 P/Al 2 O 3 > NiP 2 /Al 2 O 3 > Ni/Al 2 O 3 > imp-Ni 2 P/Al 2 O 3 catalysts (prepared by the impregnation method). Such enhanced performance of Ni 2 P/Al 2 O 3 could be ascribed to small nickel phosphide particle size and rich active Niδ+ species. Notably, the sulfur contents of PR were effectively reduced from 55.4 (C 5 PR) and 72.3 ppm (C 9 PR) to 3.8 and 7.9 ppm after hydrogenation by Ni 2 P/Al 2 O 3. Meanwhile, Ni 2 P/Al 2 O 3 also exhibited good stability with the hydrogenation degree of HC 5 PR maintaining at 94.39 % after 100 h. Our work provides a promising nickel phosphide catalyst with outstanding hydrogenation activity, hydrodesulfurization ability, and stability toward PR hydrogenation. [ABSTRACT FROM AUTHOR]

A facile strategy to regulate the structural and electronic state of Pd active sites on silica supports via Zr incorporation with different introduction sequences has been demonstrated. Pd-Zr/N-SiO 2 prepared with Zr incorporation then Pd loading exhibits superior catalytic activity for the hydrogenation of nitrile butadiene rubber. • PdZr/SiO 2 catalysts were prepared via different methods and utilized for NBR hydrogenation. • The geometric and electronic effects of Zr component on Pd active sites were revealed. • Zr can improve the catalytic activity but the sequence of Zr introduction affects the performance. Three PdZr bi-component catalysts supported on modified silica have been successfully synthesized via different Zr introduction methods and utilized for the hydrogenation of nitrile butadiene rubber (NBR) to produce high value-added hydrogenated NBR. It is demonstrated that the introduction of Zr can lead to the formation of small-sized and electron-rich Pd nanoparticles and the order of adding Zr can significantly affect the catalytic activity. In particular, the PdZr bi-component catalyst obtained by introducing Zr followed by adding Pd is found to be more stable on the silica support, which exhibits a high hydrogenation degree of 90.9% with 100% selectivity to C C bond, close to the single Pd catalyst with double Pd contents. The electronic structure and reaction mechanism analysis from density functional theory calculations further reveal that the addition of Zr component leads to negatively charged Pd species with lower energy barrier for the hydrogenation of C C bond. Our findings provide a useful guidance for the design of efficient and low-cost bi-component catalysts for the selective hydrogenation of unsaturated polymers. [ABSTRACT FROM AUTHOR]

Abstract: Hierarchically macro–mesoporous titania was synthesized by the simple dropwise addition of tetrabutyl titanate to an ammonia solution in the absence of surfactant molecules, and then calcined at different temperatures. The as-prepared titania was characterized by X-ray diffraction, N2 adsorption–desorption analysis and scanning electron microscopy. The results showed that the hierarchically marcro–mesoporous structure of the titania was well preserved after calcination at 650°C, indicating high thermal stability. The 500°C calcined titania with the hierarchically bimodal pore network was impregnated with 0.5wt.% of palladium and compared with 0.5wt.% Pd/TiO2 catalyst without such macrochannels. The novel macro–mesostructured Pd/TiO2 catalyst exhibited higher catalytic activity for styrene hydrogenation due to the lower diffusion resistance of species inside the catalyst caused by the hierarchically macro–mesoporous bimodal structure. [Copyright &y& Elsevier]