Employment Of Catalysts Research Articles

Comparative study of grass pyrolysis over regenerated catalysts: Tyre ash, zeolite, and nickel-supported ash and zeolite

This paper presents investigations on catalytic and non-catalytic grass pyrolysis conducted at 500 °C using two reactor scales: a micro-scale reactor and a laboratory fixed-bed reactor. Four catalysts were employed in the catalytic pyrolysis process: car tyre ash, commercial zeolite mordenite-sodium, nickel supported on ash, and nickel supported on zeolite. The use of catalysts reduced the production of oxygenates and promoted the formation of gaseous compounds, with the most pronounced effect observed for nickel supported on zeolite. Catalytic pyrolysis produced chars with yields that were higher than those of the non-catalytic process. The coking behaviour of the spent catalysts was evaluated by analysing carbon content, with the highest content (3 wt% C) obtained for ash after the first cycle. In the second cycle, the deposited carbon content decreased for all catalysts. Furthermore, the employment of catalysts was shown to promote the production of hydrogen, methane, and other hydrocarbons in pyrolysis gas. The higher heating value of the pyrolysis gas was the highest at 21.1 MJ/m³ when the ash catalyst was first used for pyrolysis. Reusing the pyrolysis catalysts slightly reduced the heating value of the gas to 20.3 MJ/m³ over ash and 20.6 MJ/m³ over zeolite.

First-Principles Investigation of Graphene and Fe2O3 Catalytic Activity for Decomposition of Ammonium Perchlorate.

The employment of catalysts is an effective way to improve ammonium perchlorate (AP) decomposition performance during the combustion of composite solid propellants. Understanding the micromechanism of catalysts at the atomic level, which is hard to be observed by experiments, can help attain more excellent decomposition properties of AP. In this study, first-principles simulations based on density functional theory were used to explore the effect of the graphene catalyst and iron oxide (Fe2O3) catalyst on AP decomposition. Considering the transfer of a H atom during AP decomposition, the most stable adsorption sites for aforementioned catalysts were found: the top of the C atom of the graphene surface with the adsorption energy of -0.378 eV and the top of the Fe atom of the Fe2O3 surface with the adsorption energy of -1.596 eV. On the basis of adsorption results, our transition state calculations indicate that, in comparison to control groups, graphene and Fe2O3 can reduce the activation energy barrier by ∼19 and ∼37%, respectively, to promote AP decomposition with a transfer process of a H atom on the catalyst surface. Our calculations provide a way for explaining the micromechanism of the catalytic activity of graphene and Fe2O3 nanocomposites in AP decomposition and guide experimental applications of graphene and Fe2O3 for catalytic reactions.

Zinc Chloride Mediated Nucleophilic Substitution: Amination and Thioetherification of Alcohols at Room Temperature

Catalytic chemistry is one of the focal points for the development of environmentally benign organic transformations. It is true that the employment of catalysts in organic transformations comes wi...

Recent Synthetic Methodologies Towards the Synthesis of Pyrazoles

Synthesis of pyrazole ring system has attracted a continuously growing interest of synthetic chemists because of its privileged structure and therapeutic values in medicinal chemistry. Since its discovery (by Ludwig Knorr) different methodologies for the construction of this moiety have been reported. In this review, focus has been placed on the development of novel synthetic routes/methodologies involving employment of catalysts, substrates, and so forth, during the recent years to achieve pyrazole based organic compounds via construction of pyrazole ring.

Synthesis and the field emission performances of SnO2 micrograsses

SnO2 micromaterials were synthesized via hydrothermal method at a temperature of 200 °C for 24 h without employment of catalysts or surfactants. With the dosage of the precursor (SnCl4) increasing, variable microstructures of SnO2, ophiopogon japonicas-like micrograsses, microcones, microflowers and microcorals, were obtained. The as-prepared SnO2 samples were characterized by X-ray diffraction (XRD), scanning electron microscope and energy dispersive spectrometer respectively. XRD results indicated the as-grown SnO2 samples have a tetragonal rutile structure. Among those different morphologies, micrograsses SnO2 exhibited the best field emission performance with a low turn-on field of 1.05 V/µm and a high field enhancement factor of 3880. The results are quite comparable to reported data and strongly imply the micrograsses SnO2 is a potential material for fabricating efficient emitters of display devices and vacuum electronics.

Dicationic chiral Mn(III) salen complex exchanged in the interlayers of montmorillonite clay: a heterogeneous enantioselective catalyst for epoxidation of nonfunctionalized alkenes

Dicationic chiral Mn III salen complexes 1– 4 were prepared from the reaction of 1 S,2 S-(+)-1,2-diaminocyclohexane/1 S,2 S-(−)-diphenyldiamine with 2-hydroxy-3- t-Bu-5-(triisooctylaminomethyl) benzaldehyde chloride/2-hydroxy-3- t-Bu-5-(triethylaminomethyl) benzaldehyde chloride and were exchanged in montmorillonite clay to give supported complexes 1′– 4′. Enantioselective epoxidation of styrene, indene, and 2,2-dimethyl-6-nitro chromene mediated by 1– 4 complexes (0.4–2 mol%) as catalysts in the presence of pyridine N-O as axial base with NaOCl as an oxidant gave quantitative epoxide yield (>99%) under biphasic homogeneous conditions. On employment of catalysts 1′– 4′ under similar epoxidation condition, the epoxide selectivity in the case of styrene was found to be in the range 68–74%. However, there was a significant enhancement in ee (69–70%) compared to its homogeneous catalysts 1– 4 (ee; 41–52%). Importantly, for the bulkier substrates like indene and chromene the selectivity were comparable both in homogeneous and heterogeneous system, probably due to the flexible T–O–T layers of clay allowing greater accessibility to the Mn III salen residing between the layers of clay. Further, the catalyst 1′– 4′ could be recovered easily and recycled efficiently several times by a simple separation method.

MATHEMATICAL MODELING OF HETEROGENEOUS CATALYTIC REACTORS

Abstract It is well known that in the practical employment of catalysts in commercial reactors, physical processes may play an important and even dominant role in the overall conversion scheme. Such physical processes may include mass transfer both within and external to the catalyst particles and the analogous effects of heat transport. In addition, for packed beds, dispersion of mass and heat in both the axial and radial directions may be important. The intra-particle effects arise because of the significant size of the catalyst particles which in turn is dictated by the requirement that the pressure drop within the reactor shall not be excessive. In practice, catalyst pellets up to about 1 cm in diameter are often employed.