Search Results
Efficient methylation of anilines with methanol catalysed by cyclometalated ruthenium complexes
Cyclometalated ruthenium complexes4-10allow the effective methylation of anilines with methanol to selectively giveN-methylanilines. This hydrogen autotransfer procedure proceeds under mild conditions (60 °C) in a practical manner (NaOH as base). Mechanistic investigations suggest an active homogenous ruthenium complex and β-hydride elimination of methanol as the rate determining step. © The Royal Society of Chemistry 2021.
Indirect reduction of CO2 and recycling of polymers by manganese-catalyzed transfer hydrogenation of amides, carbamates, urea derivatives, and polyurethanes
The reduction of polar bonds, in particular carbonyl groups, is of fundamental importance in organic chemistry and biology. Herein, we report a manganese pincer complex as a versatile catalyst for the transfer hydrogenation of amides, carbamates, urea derivatives, and even polyurethanes leading to the corresponding alcohols, amines, and methanol as products. Since these compound classes can be prepared using CO2as a C1 building block the reported reaction represents an approach to the indirect reduction of CO2. Notably, these are the first examples on the reduction of carbamates and urea derivatives as well as on the C-N bond cleavage in amides by transfer hydrogenation. The general applicability of this methodology is highlighted by the successful reduction of 12 urea derivatives, 26 carbamates and 11 amides. The corresponding amines, alcohols and methanol were obtained in good to excellent yields up to 97%. Furthermore, polyurethanes were successfully converted which represents a viable strategy towards a circular economy. Based on control experiments and the observed intermediates a feasible mechanism is proposed. © The Royal Society of Chemistry 2021.
Verification of impurity-related photocatalytic activity of insulating oxide supports
Photocatalysts composed of vanadium oxide species supported on commercial MgO and ZrO2 are investigated in selective methanol oxidation. Both support oxides are insulators, so the vanadium oxide species are expected as sole active component in photocatalysis. However, the pure supports showed considerable activity: Bare MgO was more active than MgO-supported vanadia catalysts, and ZrO2 showed intermediate activity. By various characterization methods, the presence of TiO2 (anatase) in the MgO support, and the presence of Zn, possibly as ZnO, in ZrO2 is demonstrated. The present study highlights that photocatalysts containing commercial supports must be carefully checked for impurity-related photocatalytic performance. © 2021 The Authors
Combination of chemo- and biocatalysis: Conversion of biomethane to methanol and formic acid
In the present day, methanol is mainly produced from methane via reforming processes, but research focuses on alternative production routes. Herein, we present a chemo-/biocatalytic oxidation cascade as a novel process to currently available methods. Starting from synthetic biogas, in the first step methane was oxidized to formaldehyde over a mesoporous VOx/SBA-15 catalyst. In the second step, the produced formaldehyde was disproportionated enzymatically towards methanol and formic acid in equimolar ratio by formaldehyde dismutase (FDM) obtained from Pseudomonas putida. Two processing routes were demonstrated: (a) batch wise operation using free formaldehyde dismutase after accumulating formaldehyde from the first step and (b) continuous operation with immobilized enzymes. Remarkably, the chemo-/biocatalytic oxidation cascades generate methanol in much higher productivity compared to methane monooxygenase (MMO) which, however, directly converts methane. Moreover, production steps for the generation of formic acid were reduced from four to two stages. © 2019 by the authors.
Design of a core-shell catalyst : an effective strategy for suppressing side reactions in syngas for direct selective conversion to light olefins
An elegant catalyst is designedviathe encapsulation of metallic oxide Zn-Cr inside of zeolite SAPO34 as a core-shell structure (Zn-Cr@SAPO) to realize the coupling of methanol-synthesis and methanol-to-olefin reactions. It can not only break through the limitation of the Anderson-Schulz-Flory distribution but can also overcome the disadvantages of physical mixture catalysts, such as excessive CO2formation. The confinement effect, hierarchical structure and extremely short distance between the two active components result in the Zn-Cr@SAPO capsule catalyst having better mass transfer and diffusion with a boosted synergistic effect. Due to the difference between the adsorption energies of the Zn-Cr metallic oxide/SAPO zeolite physical mixture and capsule catalysts, the produced water and light olefins are easily removed from the Zn-Cr@SAPO capsule catalyst after formation, suppressing the side reactions. The light olefin space time yield (STY) of the capsule catalyst is more than twice that of the typical physical mixture catalyst. The designed capsule catalyst has superior potential for scale-up in industrial applications while simultaneously extending the capabilities of hybrid catalysts for other tandem catalysis reactions through this strategy. © The Royal Society of Chemistry 2020.