Influence of Si/Al ratios on the properties of copper bearing zeolites with different framework types

Several copper containing zeolite based catalysts with different initial Si/Al and different zeolite support (types MCM-22, FAU, BETA) were synthesized or prepared from commercial precursors in a powdered and pelleted form via a direct hydrothermal synthesis and ion exchange method, and then subsequently characterized for the evaluation of their chemical, surface and catalytic properties. The characterization of the zeolites, which included the analysis of their morphological and acid-base properties, was performed by using various techniques such as the N2 physisorption, Pyridine-FTIR, XRD, SEM-EDAX and TEM. The activity and stability of the prepared catalysts were tested in the catalytic screening in a catalytic wet peroxide oxidation of the model polyphenolic wastewater. The obtained results provided an insight into the cause-and-effect relationship between the silica to alumina ratio and its direct effect on the acidity and basicity of the prepared zeolites, as well as the indirect one on their morphology, textural and surface properties of both the parent zeolite and active metal component. The use of active catalysts resulted in successfully operating the process under mild conditions with low energy consumption. It was found that the copper and iron containing catalysts showed promising activity, while the stability of the active metal component still is and remains a challenge to obtain

Reductive N-methylation of amines using dimethyl carbonate and molecular hydrogen: Mechanistic insights through kinetic modelling

[EN] Kinetic analysis of ruthenium-catalyzed reductive N-methylation of amines using dimethyl carbonate as C1 source and molecular hydrogen as reductant has been performed. Kinetic equations have been derived and kinetic modelling has been performed for experimental data generated previously at a constant hydrogen pressure as well as for additional experiments performed at different hydrogen pressures. The study has revealed interesting kinetic features related to an induction period strongly influenced by temperature. A kinetic model has been proposed based on advanced reaction mechanism featuring transformation between different type of catalytic species and inactivation of them during the reaction. Kinetic modelling was done for all data sets together showing excellent correspondence between calculations and experiments.Cabrero Antonino, JR.; Adam-Ortiz, R.; Wärnå, J.; Murzin, DY.; Beller, M. (2018). Reductive N-methylation of amines using dimethyl carbonate and molecular hydrogen: Mechanistic insights through kinetic modelling. Chemical Engineering Journal. 351:1129-1136. https://doi.org/10.1016/j.cej.2018.06.174S1129113635

Non-thermal plasma for process and energy intensification in dry reforming of methane

Plasma-assisted dry reforming of methane (DRM) is considered as a potential way to convert natural gas into fuels and chemicals under near ambient temperature and pressure; particularly for distributed processes based on renewable energy. Both catalytic and photocatalytic technologies have been applied for DRM to investigate the CH4 conversion and the energy efficiency of the process. For conventional catalysis; metaldoped Ni-based catalysts are proposed as a leading vector for further development. However; coke deposition leads to fast deactivation of catalysts which limits the catalyst lifetime. Photocatalysis in combination with non-thermal plasma (NTP), on the other hand; is an enabling technology to convert CH4 to more reactive intermediates. Placing the catalyst directly in the plasma zone or using post-plasma photocatalysis could generate a synergistic effect to increase the formation of the desired products. In this review; the recent progress in the area of NTP-(photo)catalysis applications for DRM has been described; with an in-depth discussion of novel plasma reactor types and operational conditions including employment of ferroelectric materials and nanosecond-pulse discharges. Finally, recent developments in the area of optical diagnostic tools for NTP, such as optical emission spectroscopy (OES), in-situ FTIR, and tunable diode laser absorption spectroscopy (TDLAS), are reviewed

Selectivity of the Lindlar catalyst in alkyne semi-hydrogenation: a direct liquid-phase adsorption study

We study the alkyne semi-hydrogenation selectivity over Pd and Lindlar catalyst with liquid phase adsorption. The results indicate that there are strongly-adsorbing alkyne and alkene sites; alkenes react non-selectively over the alkene adsorption sites. DFT studies indicate that the non-selective sites are low-coordination Pd atoms in the nanoparticles

On the performance of Ag/Al2O3 as a HC-SCR catalyst – influence of silver loading, morphology and nature of the reductant

This study focuses on the performance of Ag/Al2O3 catalysts for hydrocarbon selective catalytic reduction (HC-SCR) of NOx under lean conditions, using complex hydrocarbons as reductants. The aim is to elucidate the correlation towards the silver loading and morphology, with respect to the nature of the reductant. Ag/Al2O3 samples with either 2 or 6 wt% silver loading were prepared, using a sol–gel method including freeze-drying. The catalytic performance of the samples was evaluated by flow reactor experiments, with paraffins, olefins and aromatics of different nature as reductants. The physiochemical properties of the samples were characterized by scanning electron microscopy/energy dispersive X-ray spectroscopy, scanning transmission electron microscopy/high angle annular dark field imaging, X-ray photoelectron spectroscopy and N2-physisorption. The 2 wt% Ag/Al2O3 sample was found to be the most active catalyst in terms of NOx reduction. However, the results from the activity studies revealed that the decisive factor for high activity at low temperatures is not only connected to the silver loading per se. There is also a strong correlation between the silver loading and morphology (i.e. the ratio between low- and high- coordinated silver atoms) and the nature of the hydrocarbon, on the activity for NOx reduction. Calculated reaction rates over the low-coordinated step and high- coordinated terrace sites showed that the morphology of silver has a significant role in the HC-SCR reaction. For applications which include complex hydrocarbons as reductants (e.g. diesel), these issues need to be considered when designing highly active catalysts

Deactivation and regeneration of Pt-modified zeolite Beta-Bindzil extrudates in n-hexane hydroisomerization

BACKGROUND The metal-acid bifunctional catalysts are widely used in many industrially significant chemical processes, including hydroisomerization of n-hexane. Deactivation and regeneration of metal-acid bifunctional extrudates was investigated in continuous n-hexane hydroisomerization in a fixed-bed reactor. Four Pt/H-Beta-25 catalysts containing 30% Bindzil binder were prepared with the same composition and controlled metal deposition.RESULTS Different preparation steps led to differences in the mechanical strength, Pt particle size, acidity and strength, metal-to-acid site (c(Pt)/c(AS)) ratio and proximity between two types of active sites. A very slow deactivation and high selectivity to C-6 isomers was obtained when Pt was deposited on H-Beta-25 zeolite.CONCLUSION Initial selectivity to the desired products was correlated with the physicochemical properties of the catalysts. Location of the metal has a larger influence on catalyst deactivation of the bifunctional catalysts rather than the metal-to-acid site ratio or site proximity. Decline of n-hexane conversion and selectivity to C-6 isomers were correlated with changes in the textural properties and acidity of the deactivated catalyst, respectively. (c) 2021 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry

Supported silver nanoparticles as catalysts for liquid-phase betulin oxidation

The research is funded from the Russian Science Foundation project No. 18-73-00019, Tomsk Polytechnic University Competitiveness Enhancement Program, project VIU-ISHBMT-197/2020 and Tomsk Polytechnic University State Task "Science", project FSWW-2020-0011 (Russia). This work was partially supported by Fundacao para a Ciencia e a Tecnologia, Portugal, through project UIDB/00100/2020 of the Centro de Quimica Estrutural, by national funds though FCT, under the Scientific Employment Stimulus-Institutional Call (CEECINST/00102/2018) and the Associate Laboratory for Green Chemistry-LAQV financed by national funds from FCT/MCTES (UIDB/50006/2020 and UIDP/50006/2020).Herein, it has been shown that betulin can be transformed into its biologically active oxo-derivatives (betulone, betulinic and betulonic aldehydes) by liquid-phase oxidation over supported silver catalysts under mild conditions. In order to identify the main factors determining the catalytic behavior of nanosilver catalysts in betulin oxidation, silver was deposited on various alumina supports (γ-alumina and boehmite) using deposition–precipitation with NaOH and incipient wetness impregnation methods, followed by treatment in H2 or O2. Silver catalysts and the corresponding supports were characterized by X-ray diffraction, nitrogen physisorption, inductively coupled plasma optical emission spectroscopy, photoelectron spectroscopy and transmission electron microscopy. It was found that the support nature, preparation and treatment methods predetermine not only the average Ag nanoparticles size and their distribution, but also the selectivity of betulin oxidation, and thereby, the catalytic behavior of Ag catalysts. In fact, the support nature had the most considerable effect. Betulin conversion, depending on the support, increased in the following order: Ag/boehmite < Ag/boehmite (calcined) < Ag/γ-alumina. However, in the same order, the share of side reactions catalyzed by strong Lewis acid centers of the support also increased. Poisoning of the latter by NaOH during catalysts preparation can reduce side reactions. Additionally, it was revealed that the betulin oxidation catalyzed by nanosilver catalysts is a structure-sensitive reaction.publishersversionpublishe