Catalysis Surveys from Asia最新文献

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.

Here we report a strategy to prepare a novel ternary dual Z-scheme PCN/BiOCl/CdS photocatalyst by in-situ introducing bismuth oxychloride (BiOCl) on porous carbon nitride (PCN) and then depositing cadmium sulfide (CdS). The synthesized PCN/BiOCl/CdS not only has the porous structure of PCN and the wide visible-light absorption range of CdS, but a special morphology and abundant oxygen vacancies of BiOCl under the action of the structure-directing agent ethylene glycol. Through the modulation of oxygen vacancies, the BiOCl in the PCN/BiOCl/CdS can be excited under visible light, thereby further improving its optical properties. The PCN/BiOCl/CdS exhibited excellent photocatalytic activity in oxidative coupling reaction of benzylamine under visible light. The excellent catalytic performance of PCN/BiOCl/CdS photocatalyst was due to high charge separation efficiency, oxygen vacancies and visible light absorption. Finally, we proposed a feasible photocatalytic mechanism for the PCN/BiOCl/CdS in oxidative coupling reaction of benzylamine.

Carbon capture and utilization (CCU) technology is the process of capturing and converting CO₂ into useful materials for further usage. The CCU aims to convert the captured CO₂ into more valuable materials while maintaining the carbon neutrality of the production process. In this work, we have demonstrated the acetoacetate production from acetone and NaHCO₃ using acetone carboxylase (AC) in cell extract from photosynthetic bacteria Rhodobacter capsulatus strain SB1003 (Rb. capsulatus SB1003) cultured in a medium containing acetone and bicarbonate under anaerobic photoheterotrophic conditions as a catalyst in the presence of ATP. Steady acetoacetate production due to the carboxylation of acetone with NaHCO₃ was accomplished in the presence of ATP by using cell extract including AC from Rb. capsulatus SB1003. Moreover, steady acetoacetate production from acetone and gaseous CO₂ also was attained by using cell extract.

Fluidized Catalytic Cracking (FCC) is one of the key processes of any petroleum refinery as it produces gasoline, Liquefied Petroleum Gas (LPG) and valuable petrochemical feedstock viz. ethylene and propylene. FCC is a catalytic process where zeolite (USY and ZSM-5) based catalysts are being used, contain a high concentration of acidic sites, which are responsible for cracking heavy hydrocarbon molecules into smaller ones. During these cracking reactions, significant coke formation occurs over the catalyst surface and blocks the pores, thus resulting drop in catalytic activity. To regain the catalyst activity, the coke on the catalyst is burned in the FCC regenerator unit and provides heat demand for the FCC riser bed where the cracking reaction takes place and the cycle continues. The temperature of the FCC regenerator reaches around 700 °C due to the combustion of coke on the catalyst. Due to incomplete combustion of coke on catalyst produces CO which burns above the catalyst bed, which is denoted as a dilute bed. The heat of reaction of CO combustion needs to be realized on catalysts bed and also to avoid the heat loss in the regenerator dilute bed. Higher dilute bed temperature damages the FCC regenerator internals, which is to be avoided. Conventionally, additives named CO Combustion Promoters (COPs) have been used for the promotion of CO to CO₂ in the catalyst bed which helps in improving regeneration of FCC equilibrium catalysts. The present article covers the concept and various types of COP reported in the literature. Different preparation methodologies, physico-chemical properties and evaluation results have been discussed. These insights would be helpful to understand the structure–property–activity relationship of COP. Further, it can also help to select the right COP for the desired commercial applications.

Series of Ti/Cu-SSZ-13 zeolite catalysts with variable Ti content were prepared via convenient in-situ one-pot synthesizing strategy. Systematic evaluations of the NH₃-SCR catalytic performance over the obtained catalysts were conducted. Results show that Ti/Cu-SSZ-13 with appropriate Ti content (in the current work Ti_0.81/Cu_2.15-SSZ-13) could serve as capable candidate for NH₃-SCR application, as it exhibits highly efficient catalytic activity with expanded operation temperature window width from 140 to 540 °C, nearly 100% N₂ selectivity, as well as superior tolerability against water vapor and SO₂. Further structural/physicochemical characterizations demonstrate that the obtained Ti/Cu-SSZ-13 catalysts possess well-crystallized characteristic chabazite (CHA) structure. Isolated Cu²⁺ and monomeric Ti⁴⁺ are recognized as the primary active species, as the former mainly contributes to SCR reaction at low temperatures, while the latter are conducive for improving the high temperature SCR activity. Ti over doping would result in partial destruction of the zeolite structure, occupation of Cu²⁺ cation sites and formation of surface aggregated TiO_x, thus leading to unsatisfactory NH₃-SCR performances. Moreover, formation of agglomerated CuO_x species during hydrothermal ageing and blockage of surface active sites by sulfate species formed during SO₂ pretreatment are considered responsible for activity deterioration in the tolerability tests.