scholarly journals Effect of MAF-6 Crystal Size on Its Physicochemical and Catalytic Properties in the Cycloaddition of CO2 to Propylene Oxide

Catalysts ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1061
Author(s):  
Maria N. Timofeeva ◽  
Ivan A. Lukoyanov ◽  
Valentina N. Panchenko ◽  
Biswa Nath Bhadra ◽  
Evgenii Yu Gerasimov ◽  
...  
Keyword(s):  
Particle Size ◽  
Propylene Oxide ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Binary Systems ◽  
Crystal Size ◽  
Tetrabutylammonium Bromide ◽  
Textural Properties ◽  
Similar Reaction ◽  
Zeolitic Imidazolate Frameworks

Zeolitic imidazolate frameworks MAF-5 and MAF-6 based on Zn2+ and 2-ethylimidazole were demonstrated to be efficient heterogeneous catalysts in solvent-free coupling of CO2 and propylene oxide (PO) to produce propylene carbonate (PC) at 0.8 MPa of CO2 and 80 °C. Activity of MAF-5 was lower in comparison with MAF-6 due to the difference in their structural and textural characteristics. MAF-6 samples with particle size of 190 ± 20, 360 ± 30, and 810 ± 30 nm were prepared at room temperature from [Zn(NH3)4](OH)2 and 2-ethylimidazole. Control of particle size was achieved by variation of type of alcohol in alcohol/cyclohexane media for the preparation of MAF-6. According to this comprehensive study, the yield of PC was found to decrease with increasing crystal size of the MAF-6 material, which was related to the change in textural properties and the number and localization of active sites. The combination of MAF-6 with particle size of with particle size of 190 ± 20 nm and tetrabutylammonium bromide ([n-Bu4N]Br) as co-catalyst led to an approximately 4-fold enhancement in the yield of PC (80.5%). Compared with reported ZIFs catalysts, the efficiencies of MAF-5/[n-Bu4N]Br and MAF-6/[n-Bu4N]Br binary systems were comparable and higher under similar reaction conditions.

Zeolitic Imidazolate Frameworks ZIF-8 and MAF-5 as Highly Efficient Heterogeneous Catalysts for Synthesis of 1-Methoxy-2-propanol from Methanol and Propylene Oxide

2019 ◽  
Vol 58 (25) ◽  
pp. 10750-10758 ◽  
Author(s):  
Maria N. Timofeeva ◽  
Ivan A. Lykoyanov ◽  
Valentina N. Panchenko ◽  
Kristina I. Shefer ◽  
Biswa Nath Bhadra ◽  
...  
Keyword(s):  
Propylene Oxide ◽  
Heterogeneous Catalysts ◽  
Zeolitic Imidazolate Frameworks ◽  
Highly Efficient

scholarly journals Biodiesel: Modified Mixed Oxides as Catalyst for Transesterification of Rapeseed Oil

Catalysts ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1397
Author(s):  
Vávra Aleš ◽  
Tišler Zdeněk ◽  
Kocík Jaroslav ◽  
Smutek Jakub
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Fossil Fuels ◽  
Mixed Oxides ◽  
Catalyst Activity ◽  
Textural Properties ◽  
Carbon Fibres ◽  
Key Factor ◽  
Double Hydroxides

Biodiesel, as one of the alternative biofuels replacing the common fossil fuels, is prepared by transesterification of oils and fats. Commonly, the reaction is catalysed by either acidic or basic catalysts. The availability of the active sites to large triglyceride molecules is the key factor of the heterogeneous catalysts. The use of carbon fibres during the synthesis of Mg/Fe layered double hydroxides results in the formation of macropores during the calcination. The amount of carbon fibres showed an important effect on the textural properties of the resulting mixed oxides. The texture was determined by N2-adsorption and Hg-porosity. The catalyst activity in the studied reaction was examined by determination of ester amount by gas chromatography and the activity was compared with unmodified mixed oxides. The highest ester yield (40 wt.%) was achieved by adding 1 wt.% of carbon fibres to the catalyst with the largest size of macropores.

What catalysis needs from the electron microscopist

1988 ◽  
Vol 46 ◽  
pp. 694-695
Author(s):  
Alexis T. Bell
Keyword(s):  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Catalyst Deactivation ◽  
Surface Composition ◽  
Internal Surface ◽  
Active Phase ◽  
Atomic Scale ◽  
Metal Catalyst ◽  
Internal Surface Area ◽  
Porous Support

Heterogeneous catalysts, used in industry for the production of fuels and chemicals, are microporous solids characterized by a high internal surface area. The catalyticly active sites may occur at the surface of the bulk solid or of small crystallites deposited on a porous support. An example of the former case would be a zeolite, and of the latter, a supported metal catalyst. Since the activity and selectivity of a catalyst are known to be a function of surface composition and structure, it is highly desirable to characterize catalyst surfaces with atomic scale resolution. Where the active phase is dispersed on a support, it is also important to know the dispersion of the deposited phase, as well as its structural and compositional uniformity, the latter characteristics being particularly important in the case of multicomponent catalysts. Knowledge of the pore size and shape is also important, since these can influence the transport of reactants and products through a catalyst and the dynamics of catalyst deactivation.

Continuous Precipitation of Lead Iodide

1994 ◽  
Vol 59 (7) ◽  
pp. 1503-1510
Author(s):  
Stanislav Žáček ◽  
Jaroslav Nývlt
Keyword(s):  
Growth Rate ◽  
Particle Size ◽  
Crystal Size ◽  
Crystal Growth Rate ◽  
Laboratory Model ◽  
Lead Iodide ◽  
Secondary Nucleation ◽  
Equimolar Ratio ◽  
Continuous Precipitation ◽  
The Mean

Lead iodide was precipitated from aqueous solutions of 0.015 - 0.1 M Pb(NO3)2 and 0.03 - 0.2 M KI in the equimolar ratio using a laboratory model of a stirred continuous crystallizer at 22 °C. After reaching the steady state, the PbI2 crystal size distribution was measured sedimentometrically and the crystallization kinetics was evaluated based on the mean particle size. Both the linear crystal growth rate and the nucleation rate depend on the specific output of the crystallizer. The system crystallization constant either points to a significant effect of secondary nucleation by the mechanism of contact of the crystals with the stirrer blade, or depends on the concentrations of the components added due to the micromixing mechanism.

Batch Precipitation of Lead Iodide

1994 ◽  
Vol 59 (6) ◽  
pp. 1301-1304
Author(s):  
Jaroslav Nývlt ◽  
Stanislav Žáček
Keyword(s):  
Aqueous Solution ◽  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Crystal Size ◽  
Lead Nitrate ◽  
Lead Iodide ◽  
Constant Rate ◽  
Mean Size ◽  
The Mean

Lead iodide was precipitated by a procedure in which an aqueous solution of potassium iodide at a concentration of 0.03, 0.10 or 0.20 mol l-1 was stirred while an aqueous solution of lead nitrate at one-half concentration was added at a constant rate. The mean size of the PbI2 crystals was determined by evaluating the particle size distribution, which was measured sedimentometrically. The dependence of the mean crystal size on the duration of the experiment exhibited a minimum for any of the concentrations applied. The reason for this is discussed.

A Convenient Method for Preparing Well-Dispersed Er2Zr2O7 Nanocrystals

2010 ◽  
Vol 123-125 ◽  
pp. 611-614 ◽  
Author(s):  
Yu Ping Tong ◽  
Rui Zhu Zhang ◽  
Shun Bo Zhao ◽  
Chang Yong Li
Keyword(s):  
Particle Size ◽  
Combustion Synthesis ◽  
Crystal Size ◽  
Lattice Distortion ◽  
Combustion Method ◽  
Treatment Temperature ◽  
Synthesis Process ◽  
Thermal Treatment Temperature ◽  
Average Size ◽  
Xrd And Tem

Well-dispersed fluorite Er2Zr2O7 nanocrystals have been successfully prepared by a convenient salt-assistant combustion method. The effects of calcinations temperature and salt category on the characteristics of the products were investigated by XRD and TEM. The thermal treatment temperature has an important effect on crystal size and lattice distortion of the nanocrystals. The experiment showed that the introduction of salt in the combustion synthesis process resulted in the formation of well-dispersed Er2Zr2O7 nanocrystals. The average size was 30 nm and was in agreement with the XRD result, which indicated that the nanocrystals were uniform in particle size distribution. Moreover, the possible formation process in the salt-assisted combustion synthesis was also analyzed.

A direct reaction approach for the synthesis of zeolitic imidazolate frameworks: template and temperature mediated control on network topology and crystal size

2012 ◽  
Vol 48 (79) ◽  
pp. 9930 ◽  
Author(s):  
Mónica Lanchas ◽  
Daniel Vallejo-Sánchez ◽  
Garikoitz Beobide ◽  
Oscar Castillo ◽  
Andrés T. Aguayo ◽  
...  
Keyword(s):  
Network Topology ◽  
Crystal Size ◽  
Direct Reaction ◽  
Zeolitic Imidazolate Frameworks

scholarly journals Pyrolyzing Renewable Sugar and Taurine on the Surface of Multi-Walled Carbon Nanotubes as Heterogeneous Catalysts for Hydroxymethylfurfural Production

Catalysts ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 517 ◽  
Author(s):  
Huiping Ji ◽  
Jie Fu ◽  
Tianfu Wang
Keyword(s):  
Carbon Nanotubes ◽  
Heterogeneous Catalysts ◽  
Metal Salt ◽  
Textural Properties ◽  
Solvent System ◽  
Hydrothermal Stability ◽  
Transportation Fuels ◽  
Water Solvent ◽  
Multi Walled Carbon Nanotubes ◽  
Walled Carbon Nanotubes

Conversion of biorenewable feedstocks into transportation fuels or chemicals likely necessitates the development of novel heterogeneous catalysts with good hydrothermal stability, due to the nature of highly oxygenated biomass compounds and the prevalence of water as a processing solvent. The use of carbon-based materials, derived from sugars as catalyst precursors, can achieve hydrothermal stability while simultaneously realizing the goal of sustainability. In this work, the simultaneous pyrolysis of glucose and taurine in the presence of multi-walled carbon nanotubes (MWCNTs), to obtain versatile solid acids, has been demonstrated. Structural and textural properties of the catalysts have been characterized by TEM, TGA, and XPS. Additionally, solid state nuclear magnetic resonance (ssNMR) spectroscopy has been exploited to elucidate the chemical nature of carbon species deposited on the surface of MWCNTs. Al(OTf)3, a model Lewis acidic metal salt, has been successfully supported on sulfonic groups tethered to MWCNTs. This catalyst has been tested for C6 sugar dehydration for the production of HMF in a tetrahydrofuran (THF)/water solvent system with good recyclability.

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