Direct gas-phase photocatalytic epoxidation of propylene with molecular oxygen by photocatalysts
TL;DR: In this article, a series of photocatalysts including SiO2, TiO2 and V-Ti/MCM-41 were evaluated for photo-epoxidation of propylene.
About: This article is published in Chemical Engineering Journal.The article was published on 2012-01-01. It has received 30 citations till now. The article focuses on the topics: Propylene oxide & Propionaldehyde.
Citations
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TL;DR: Comprehensive and successful strategies for enhancing the selectivity in photocatalysis are abridged to reinvigorate and stimulate future investigations.
Abstract: Photocatalysis has been invariably considered as an unselective process (especially in water) for a fairly long period of time, and the investigation on selective photocatalysis has been largely neglected. In recent years, the field of selective photocatalysis is developing rapidly and now extended to several newer applications. This review focuses on the overall strategies which can improve the selectivity of photocatalysis encompassing a wide variety of photocatalysts, and modifications thereof, as well as the related vital processes of industrial significance such as reduction and oxidation of organics, inorganics, and CO2 transformation. Comprehensive and successful strategies for enhancing the selectivity in photocatalysis are abridged to reinvigorate and stimulate future investigations. In addition, nonsemiconductor type photocatalysts, such as Ti–Si molecular sieves and carbon quantum dots (CQDs), are also briefly appraised in view of their special role in special selective photocatalysis, namely e...
579 citations
TL;DR: In the presence of only molecular oxygen as oxidant and in absence of reducing agents, a number of liquid-phase and gas-phase catalytic reactions have been reported as discussed by the authors.
Abstract: The direct oxidation of propylene to propylene oxide (PO) using molecular oxygen has many advantages over existing chlorohydrin and hydroperoxide process, which produce side products and require complex purification schemes. Recent advances in liquid-phase and gas-phase catalytic oxidation of propylene in the presence of only molecular oxygen as oxidant and in absence of reducing agents are summarized. Liquid-phase PO processes involving soluble or insoluble Mo, W, or V catalysts have been reported which provide moderate conversions and selectivities, but these likely involve autoxidation by homogeneous chain reactions. Gas-phase PO catalysts have been mostly Ag-, Cu-, or TiO2-based substances, although other compositions such as Au-, MoO3-, Bi-based catalysts and photocatalysts have also been suggested as possibilities. The Ag catalysts differ from those used for ethylene oxide production in having high Ag contents and numerous additives. The additives are solid-phase alkali metals, alkaline earth metals...
141 citations
TL;DR: In this paper, a charge transfer of S-scheme heterojunctions involving a reduction and oxidation photocatalyst in staggered band arrangement with Fermi level differences is discussed.
Abstract: Solar radiation is a sustainable, unlimited source of energy for electricity and chemical reactions, yet the conversion efficiency of actual processes is limited and controlled by photocarriers migration and separation. Enhancing the conversion efficiency would require to suppress the recombination of photogenerated electron–hole pairs and improve the low redox potentials. This can be done during the growth of step-scheme (S-scheme) heterojunctions. Here we review the charge transfer of S-scheme heterojunctions involving a reduction and oxidation photocatalyst in staggered band arrangement with Fermi level differences. We present factors determining the validation of the S-scheme mechanism with respective characterization techniques, including in situ and ex situ experiments, and theoretical studies. We show mechanistic drawbacks of traditional photocatalytic systems to highlight the advantages of S-scheme photocatalysts. We describe co-catalyst loading, bandgap tuning, and interfacial optimization that ultimately achieve highly efficient photocatalysis. Last, application for water splitting, CO2 conversion, pollutant degradation, bacterial inactivation and others is discussed.
129 citations
TL;DR: In this paper, the authors review the photocatalytic mechanism, properties, synthesis and application to wastewater treatment of cadmium sulfide (CdS) photocatalyst.
Abstract: Global energy demand and pollution are calling for advanced materials such as visible light semiconductor photocatalysts. In particular, cadmium sulfide (CdS) appears promising due to its tunable bandgap, high absorption of visible light and excellent optical properties. Here we review the photocatalytic mechanism, properties, synthesis and application to wastewater treatment of CdS photocatalysts. Strategies to improve photocatalytic performance include heteroatom doping, heterojunction formation, morphology and crystallinity modification, hybridization with co-catalysts and the use of carbon materials.
125 citations
TL;DR: In this article, the epoxidation of propylene with H 2 O 2 catalyzed by a supported TS-1 catalyst in a fixed-bed reactor has been studied and the effects of methanol concentration, hydrogen peroxide concentration, propylene pressure and temperature on the reaction were investigated.
78 citations
References
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TL;DR: Water photolysis is investigated by exploiting the fact that water is transparent to visible light and cannot be decomposed directly, but only by radiation with wavelengths shorter than 190 nm.
Abstract: ALTHOUGH the possibility of water photolysis has been investigated by many workers, a useful method has only now been developed. Because water is transparent to visible light it cannot be decomposed directly, but only by radiation with wavelengths shorter than 190 nm (ref. 1).
27,819 citations
TL;DR: In this paper, the effect of the zinc precursor type, the aging of the starting solution, the substrate temperature and a vacuum-annealing treatment on the electrical, morphological, structural and optical properties was studied, in order to obtain conductive and transparent zinc oxide thin films.
2,780 citations
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01 Jan 1995
2,571 citations
TL;DR: In this article, the effects of solution pH and temperature on the adsorption of fluoride onto bone char made from cattle bones were investigated, and it was found that the maximum adaption took place at pH 3.
Abstract: The effects of solution pH and temperature on the adsorption of fluoride onto bone char made from cattle bones were investigated in this work. It was found that the maximum adsorption took place at pH 3 and the adsorption capacity decreased nearly 20 times augmenting the pH from 3 to 12. This behavior was attributed to the electrostatic interactions between the surface of bone char and the fluoride ions in solution. The adsorption capacity was not influenced by temperature in the range from 15 to 35 °C. A comparison of fluoride adsorption capacities among several adsorbents revealed that the adsorption capacity of the bone char was 2.8 and 36 times greater than those of a commercial activated alumina (F-1) and a commercial activated carbon (F-400). The adsorption capacity is considerably dependent upon the physicochemical properties of the bone char surface and the solution pH.
1,865 citations
TL;DR: In this article, the results of the transesterification of sunflower oil with methanol to produce biodiesel using CaO nanoparticles supported on NaX zeolite as catalyst were reported.
Abstract: Biodiesel is produced by the transesterification of oil triglycerides with methanol or ethanol, in the presence of a homogeneous or heterogeneous catalyst. This study aims to report the results of the transesterification of sunflower oil with methanol to produce biodiesel using CaO nanoparticles supported on NaX zeolite as catalyst. The effect of the CaO nanoparticles concentration on the NaX zeolite surface was studied in the range of 5−25 wt %. The transesterification reaction was carried out at reflux temperature of methanol, atmospheric pressure, a reaction time of 6 h, and with a 6:1 molar ratio of methanol to sunflower oil. Catalyst characterization was carried out by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. It was concluded that methyl esters content is highly influenced by basicity and that the best catalyst was the one holding 16 wt % CaO nanoparticles. The produced biodiesel was 93.5% methyl esters and was found to fulfill the specifications of Europ...
1,687 citations