Catalysis Surveys from Asia最新文献

Selective hydrogenation of anthraquinone is critical in producing H₂O₂, the strong oxidant widely used in most industrial areas. More efforts were made on the selective hydrogenation of C=O in the anthraquinone process because the sides-product will negatively affect continuous H₂O₂ production and significantly reduce the project economics. A crucial step toward high H₂O₂ yield is the rational design of heterogeneous catalysts. In this review, the metal-based catalyst design for the selective anthraquinone hydrogenation is cataloged into two significant strategies: active metal regulation and support property regulation. Research accomplished in the past decade on the catalyst design for selective anthraquinone hydrogenation is systematically reviewed. The focus is on the catalytic performance-enhancing mechanism and the factors that influence the mechanism. In addition, the limitations and barriers encountered for supported catalysts in the current study, as well as potential research trends, are discussed.

Co-based catalysts were derived from CoAl-layered double hydroxide (LDH), LDH/melamine, LDH/activated carbon, and LDH/g-C₃N₄. The use of these catalysts for the hydrogenation of γ-valerolactone into 1,4-pentanediol was investigated. The catalyst derived from CoAl-LDH/g-C₃N₄ contained higher concentrations of strong Brønsted acid, Lewis acid (Co^δ+, δ > 2), and Lewis base (N with a lone pair of electrons) sites, resulting in improved turnover frequency.

Nitrogen-doped carbon with and without Fe additives is a promising alternative for commercial Pt/C catalysts for the oxygen reduction reaction (ORR) in proton and anion exchange membrane fuel cells. To understand the nature of the rate-determining steps (RDSs) of the ORR over newly developed catalysts, the analysis of the Tafel slopes of ORR voltammograms is beneficial for elucidating the number of electrons involved in the RDS. Conventionally, the Tafel slope is evaluated from the measured total current, which involves several different reaction pathways: the four-electron pathway from O₂ to H₂O described with a kinetic constant k₁, the two-electron pathway from O₂ to H₂O₂ with k₂, and the two-electron pathway from H₂O₂ to H₂O with k₃. This method provides reasonable Tafel slopes as long as the measured ORR is selective to a particular reaction pathway, such as the four-electron pathway over a Pt/C catalyst; however, typical Fe/N/C and N/C catalysts have mixed reaction pathways and analyzing the Tafel slopes from the total current does not provide meaningful information. To address this, we propose a new methodology for analyzing Tafel slopes. In this study, the measured ORR currents were converted into inherent kinetic constants (k₁⁰, k₂⁰, and k₃⁰) using the Nabae model, which was previously developed by our group, and the Tafel plots for k₁⁰, k₂⁰, and k₃⁰ were analyzed to determine the Tafel slopes of each reaction pathway. Four ORR systems (Fe/N/C and N/C catalysts in acid and base) were analyzed using the proposed method, and the differences in the reaction mechanisms were successfully reflected in the determined parameters.

New organic-inorganic mesoporous hybrid materials containing terbium complexes covalently attached to mesoporous silica SBA-15 have been successfully prepared. The mesoporous silica SBA-15 was modified with 3,4,5-tri hydroxyphenyl acetic acid ligand and then used to fabricate the lanthanide-based mesoporous material SBA-15@3,4,5-tri hydroxyphenyl acetic@ Tb. The mesoporous material was characterized by Fourier transforms infrared (FTIR) spectra, powder X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results show that the 3,4,5-tri hydroxyphenyl acetic acid ligand and Tb ions are attached to the SBA-15 host. The catalysts were tested in the synthesis of 5-substituted 1H-tetrazoles. This catalyst is an efficient catalyst for [3 + 2] cycloaddition with NaN₃ to prepare 5-substituted 1H-tetrazoles. The catalyst was recycled for up to six cycles without significant loss of activity.

CO₂ (dry) reforming of methane (DRM) is a significant and useful reaction from the standpoint of effective utilization and conversion of two main greenhouse gases to value-added synthesis gas. To achieve highly efficient and stable DRM reaction, a Silicalite-1-encapsulated ultrafine Ni nanoparticle catalyst (Ni@S-1)by using Ni phyllosilicate (Ni-PS) as precursor was newly developed. This Ni@S-1 catalyst exhibited negligible coke deposition (0.5 wt.%) evaluated at 600 °C for 5 h. Additionally, this Ni@S-1 catalyst presented high and stable catalytic performances and maintained the Ni nanoparticles with ultrafine size (< 7 nm) at 850 °C for 24 h. Therefore, this Ni@S-1 catalyst showed good suppression of coke formation and high resistance to nickel sintering and thus was promising for DRM reaction.

Thermal treatment of MgO-loaded Ir nanoparticles or Ir(OAc)₃ formed Ir–MgO solid solutions. The valence of Ir in the Ir–MgO solid solution was 3 +, as evidenced by Ir L₃-edge XANES combined with XPS analysis. A slight contraction of the Ir–O bond distance was observed compared to that of the nearest neighboring Mg–O bond in MgO. Ir–MgO dispersion exhibited a two-spike pattern depending on the treatment temperature owing to the formation and successive segregation of the solid solutions.

Hydrogenation of xylose to xylitol with carbon-supported Cu catalyst (Cu@C) at a hydrogen pressure value below 1.1 MPa was performed. The Cu@C catalyst exhibited high xylitol selectivity and catalyst stability because of the inertness of the carbon support and the embedded structure of the small Cu particles in the carbon.

Solid acid catalysts of MgO–Al₂O₃ mixed oxides containing B₄O₇²⁻, HPO₄²⁻, Mo₇O₂₄⁶⁻, MoO₄²⁻, WO₄²⁻, and SO₄²⁻ were synthesized by anion exchange with Cl⁻ located in the space between anionic layers of hydrotalcite, followed by heat treatment at 773 K. The distance between the hydroxide layers was expanded by the intercalation of oxyanions larger than Cl⁻. The exchange of oxyanions in the interlayer space was confirmed by IR spectroscopy. Acid sites were generated on the obtained mixed oxides of MgO–Al₂O₃ by the electron withdrawing effect of the oxyanions. The acid catalyzed ethanol dehydration into ethylene and diethyl ether took place on the obtained catalysts. The effect of exchanged anions in the generation of acid sites was the largest in SO₄²⁻.

A combination of two base-metal oxides in tandem configuration can realize three-way reaction without platinum group metals. For this purpose, catalysts for hydrocarbon preferential oxidation (HC-PROX) and for NO reduction by CO are required. For the design of HC-PROX catalysts, competitive oxidation of propene and CO on spinel-type MFe₂O₄ (M = Co, Cu, Mg, Mn, Ni, Zn) was investigated. MnFe₂O₄ preferentially oxidized propene in the co-presence of CO showing the best propene oxidation activity. Among the series of MFe₂O₄, the activity controlling factor was correlated to the M-O bond energy of the second metal oxides, and the preference for HC oxidation was dependent on the electronegativity of the second ion. A tandem catalyst using MnFe₂O₄ for HC-PROX and CuCo₂O₄ for NO-CO reaction showed TWC activity comparable to a Rh/CeO₂.

One-pot synthesis of menthol from citronellal or citral was summarized. Both batch and continuous reactors have been recently applied. This reaction is very complex and a bifunctional catalyst exhibiting especially Lewis acid sites for cyclisation of citronellal to isopulegol are needed, while metal particles are required for its hydrogenation to menthols. Typically, too mild acidity of the catalyst and small particles do not catalyze menthol formation. Furthermore, too high acidity causes catalyst deactivation and dehydration of menthol. Very high menthol yields have been obtained in batch reactor over nobel and transition metal supported bifunctional catalysts. Shape selectivity was demonstrated for Ni-supported on Zr-modified beta zeolite, which gave high diastereoselectivity to the desired L-menthol. Recently one-pot synthesis of menthol in a trickle bed reactor has been investigated. Catalyst suffers only minor deactivation in transformation of citronellal to menthol, while more severe catalyst deactivation occurred in transforming citral to menthols. Noteworthy from the industrial point of view is that the product distribution obtained with the same catalyst under kinetic regime or under diffusional limitations differs from each other. The metal location and synthesis method of extrudates can have a major effect on the catalyst performance. Kinetic modelling of the data obtained from the trickle bed reactor considering the effectiveness factor is discussed.

Graphical Abstract

The results from one-pot synthesis of menthol finding applications in pharmaceuticals and fragrances from citral and its hydrogenated product, citronellal over bifunctional catalysts metal–acid are summarized. The relationship between the catalyst properties and the performance is discussed. In the continuous mode catalyst deactivation becomes apparent and in such mode of operation the product distribution might differ from those obtained in a batch reactor.