Search results for "HETEROGENEOUS CATALYSIS"
showing 10 items of 233 documents
Influence of the preparative route on the properties of WOx–ZrO2 catalysts: A detailed structural, spectroscopic, and catalytic study
2007
Abstract Two series of tungstated zirconia (WZ) solid acids covering a wide range of tungsten surface densities ( δ, W at/nm2 ) were prepared by nonconventional impregnation and coprecipitation routes, leading to samples with enhanced surface area ( ∼ 70 – 120 m 2 / g ) on annealing at 973–1073 K. The materials were thoroughly characterized by N2 physisorption , XRD, Raman, XPS, H 2-TPR, and DR UV–vis spectroscopy. The catalytic behavior of the Pt-promoted WZ catalysts (1 wt% Pt) was evaluated for the hydroconversion of n-hexadecane used as model feed representative of Fischer–Tropsch waxes. Both series of catalysts displayed a pronounced maximum in the reaction rate and a minimum in the se…
Oscillatory Reactions in Heterogeneous Catalysis
1993
Publisher Summary This chapter focuses on the oscillatory reactions in heterogeneous catalysis. Oscillations are possible on all levels in a catalytic reactor, from the single-crystal plane to the crystallite to the catalyst pellet to the packed-bed reactor, and each level adds another degree of complexity. So, it is necessary to isolate the major influences at each level and to separate the characteristics of the oscillations on one level from the effects caused by coupling with other levels. Only when each level is well understood is it possible to fully understand the overall oscillatory behavior. Oscillations in heterogeneous catalysis, therefore, remain an intriguing and demanding prob…
Cyclocarbonylation reactions of allylphenols and allylnaphthols catalyzed by Pd/C- 1,4-bis(diphenylphosphine)butane
2002
Palladium/activated carbon (Pd/C) in the presence of 1,4-bis(diphenylphosphino)butane is an efficient heterogeneous catalyst for cyclocarbonylation reactions of 2-allyl phenols affording five-, six-, and seven-membered ring lactones. Various examples of cyclocarbonylation are reported and the regioselectivity is compared with the homogeneous system. Both commercial Pd/C and Pd/C prepared from activated carbons obtained from vegetable and polymeric wastes are investigated.
Partial Reduction and Selective Transfer of Hydrogen Chloride on Catalytic Gold Nanoparticles
2017
© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim HCl in solution accepts electron density from Au NPs and partially reduces at room temperature, as occurs with other simple diatomic molecules, such as O2 and H2. The activation can be run catalytically in the presence of alkynes to give exclusively E-vinyl chlorides, after the regio- and stereoselective transfer of HCl. Based also on this method, vinyl chloride monomer (VCM) can be produced in a milder and greener way than current industrial processes.
Elementary steps in heterogeneous catalysis: The basis for environmental chemistry
2018
Abstract Catalysis is an alternative way for reaching an immediate formation of a product, because of a lower energy barrier (between the molecules and the catalysts). Heterogeneous catalysis comprises the acceleration of a chemical reaction through interaction of the molecules involved with the surface of a solid. It is a discipline, which involves all the different aspects of chemistry: inorganic and analytical chemistry in order to characterize the catalysts and the forms of these catalysts. The industrial chemistry puts all these things together to understand the solid chemical handling, chemical reaction and energy engineering and the heat and mass transfer in these catalytic processes…
Heterogeneous catalytic degradation of phenolic substrates: catalysts activity
2009
This review article explored the catalytic degradation of phenol and some phenols derivates by means of advanced oxidation processes (AOPs). Among them, only the heterogeneous catalyzed processes based on catalytic wet peroxide oxidation. catalytic ozonation and catalytic wet oxidation were reviewed. Also selected recent examples about heterogeneous photocatalytic AOPs; will be presented. In details, the present review contains: (i) data concerning catalytic wet peroxide oxidation of phenolic compounds over metal-exchanged zeolites, hydrotalcites, metal-exchanged clays and resins. (ii) Use of cobalt-based catalysts, hydrotalcite-like compounds, active carbons in the catalytic ozonation proc…
Electrochemical treatment of aqueous solutions of organic pollutants by electro-Fenton with natural heterogeneous catalysts under pressure using Ti/I…
2018
The treatment of toxic organic pollutants by electro-Fenton (EF) presents some drawbacks such as the necessity to work at low pH and the low solubility of oxygen in water contacted with air or oxygen at room pressure that results often in slow and relatively low abatements. Here, the coupled adoption of natural heterogeneous catalysts and of relatively high pressure was proposed in order to improve the performances of EF for the treatment of organic pollutants. Caffeic acid (CA) and 3-chlorophenol were used as model resistant organic pollutants. EF process was performed using both conventional homogeneous FeSO4 and natural heterogeneous catalysts (pyrite, chalcopyrite, Fe2O3 and Fe3O4) as i…
Azo-Dyes Photocatalytic Degradation in Aqueous Suspension of TiO2 Under Solar Irradiation
2002
Abstract The photodegradation of two common and very stable azo-dyes, i.e. methyl-orange (C14H14N3SO3Na) and orange II (C16H11N2SO4Na), is reported. The photocatalytic oxidation was carried out in aqueous suspensions of polycrystalline TiO2 irradiated by sunlight. Compound parabolic collectors, installed at the “Plataforma Solar de Almeria” (PSA, Spain) were used as the photoreactors and two identical reacting systems allowed to perform photoreactivity runs for the two dyes at the same time and under the same irradiation conditions. The disappearance of colour and substrates together with the abatement of total organic carbon content was monitored. The main sulfonate-containing intermediate…
Iron-based metal-organic framework: Synthesis, structure and current technologies for water reclamation with deep insight into framework integrity.
2021
Water is a supreme requirement for the existence of life, the contamination from the point and non-point sources are creating a great threat to the water ecosystem. Advance tools and techniques are required to restore the water quality and metal-organic framework (MOFs) with a tunable porous structure, striking physical and chemical properties are an excellent candidate for it. Fe-based MOFs, which developed rapidly in recent years, are foreseen as most promising to overcome the disadvantages of traditional water depolluting practices. Fe-MOFs with low toxicity and preferable stability possess excellent performance potential for almost all water remedying techniques in contrast to other MOF…
Imidazolium-Functionalized Carbon Nanohorns for the Conversion of Carbon Dioxide
2016
Six new hybrid materials composed of carbon nanohorns (CNHs) and highly cross-linked imidazolium salts were easily synthesized using a one-step procedure based on the radical oligomerization of bis-vinylimidazolium salts (bVImiX) in the presence of pristine CNHs. The hybrid materials were characterized and employed as the sole catalysts for the conversion of carbon dioxide into cyclic carbonate by reaction with epoxides. The solids displayed excellent turnover number and productivity. Moreover, four catalysts were investigated in recycling experiments. Two catalysts containing an octyl linker between the imidazolium units and a bromide or an iodide anion showed no loss in activity after thr…