Direct epoxidation of propylene to propylene oxide with molecular oxygen over Ag–Mo–W/ZrO2 catalysts
TL;DR: In this paper, a series of Ag(x)Mo(5-x)W/ZrO 2 (x = 5, 3.75, 2.50, 1.25, and 0) catalysts with different molybdenum content (x, wt%) were prepared by a slurry method.
About: This article is published in Catalysis Communications.The article was published on 2017-01-10. It has received 19 citations till now. The article focuses on the topics: Propylene oxide & Catalysis.
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TL;DR: Propylene oxide (PO) is a versatile chemical, mainly used in the synthesis of polyurethane plastics as mentioned in this paper, and it can be epoxidized using molecular oxygen to replace the tedious current synthesis protoco...
Abstract: Propylene oxide (PO) is a versatile chemical, mainly used in the synthesis of polyurethane plastics. Propylene epoxidation using molecular oxygen could replace the tedious current synthesis protoco...
62 citations
25 Oct 2019
40 citations
TL;DR: In this article, the silylated Pd/Ti-MCM-41 (PdTM-ZS) catalysts were applied as efficient catalysts for the selective production of propylene oxide from the oxidation of cumene hydroperoxide as the oxidant.
35 citations
TL;DR: In this article, the effect of Cl− loading on Cu2O nanocubes enclosed by (100) facets for the direct epoxidation of propylene by molecular oxygen was explored.
12 citations
TL;DR: The discovered allyl radical formation pathway from propylene oxide is found as the most probable successive reaction pathway because of the high desorption barrier of PO.
Abstract: Propylene oxide (PO) is one of the 50 most produced chemicals according to the production volume. Environmental and economic drawbacks of conventional PO production processes necessitate new production methods. Among the new production alternatives, direct epoxidation of propylene to propylene oxide by molecular oxygen is a highly desired method and seen as the holy grail of propylene epoxidation studies. In this study, the propylene epoxidation mechanism on an Ag2O(001) surface is investigated computationally by means of density functional theory (DFT) calculations using the Vienna Ab-initio Simulation Package (VASP). A perfect Ag2O(001) surface and a surface with one O vacancy are utilized for this purpose. It is found that propylene oxide can be directly formed on an Ag2O(001) surface whether there is an oxygen vacancy or not. The rate controlling step is PO desorption from both surfaces. PO isomers, i.e. acetone and propanal, can also be formed on these surfaces. However, activation barriers do exist for these molecules. Direct allyl formation on the Ag2O(001) surface is found to be unfavorable unlike what is proposed in the literature. On the other hand, it is observed that an allyl radical can be formed either via an oxametallocycle path or after the formation of propylene oxide. In fact, the discovered allyl radical formation pathway from propylene oxide is found as the most probable successive reaction pathway because of the high desorption barrier of PO.
12 citations
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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 series of supported Ag catalysts was studied for propylene epoxidation with molecular oxygen as the oxidant, and the highest selectivity was obtained on a ball-milled catalyst with a silver loading of 56.1% supported on CaCO3 and promoted with 1.5% NaCl (Ag(56)−NaCl(1)/CaCO3).
Abstract: In this work a series of supported Ag catalysts was studied for propylene epoxidation with molecular oxygen as the oxidant. It was found that α-Al2O3 and CaCO3 were suitable supports for propylene epoxidation and that on the latter Ag particles between 400 and 700 nm gave the highest selectivity to propylene oxide (PO). Ball-milling treatment of the CaCO3 catalyst and promotion with NaCl resulted in improved catalytic performance. The highest PO selectivity (45%) was obtained on a ball-milled catalyst with a silver loading of 56 wt.% supported on CaCO3 and promoted with 1 wt.% NaCl (Ag(56)–NaCl(1)/CaCO3). The catalysts were tested with reactant flow rates of C3H6:O2:He = 5:10:15 cm3 min−1, a gas hourly space velocity (GHSV) of 1800 h−1, a reaction pressure of 0.3 MPa, and a reaction temperature of 533 K (260 °C). Addition of 500 ppm of ethyl chloride (EtCl) to the reactant gases enhanced the stability of the Ag(56)–NaCl(1)/CaCO3 catalyst. X-ray diffraction (XRD) of the Ag(56)–NaCl(1)/CaCO3 catalyst detected the existence of AgCl in the catalyst and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy confirmed the presence of surface Ag+ species. Scanning electron microscopy showed a roughening of the Ag particles by the ball-milling treatment as well as by the addition of NaCl. The effect of NaCl on the enhancement of the catalytic performance was probably due to both physical and electronic changes in the properties of the catalyst. The NaCl not only helped increase the dispersion of the silver on the CaCO3 support, but also probably increased the quantity of electrophilic oxygen species favorable for epoxidation. In situ UV–vis spectra suggested that the rapid reduction of Ag+ species on the surface of the Ag(56)–NaCl(1)/CaCO3 catalyst could be the cause of a decline in PO selectivity observed during reaction.
105 citations
TL;DR: In this article, it was shown that the comparatively low selectivity to propylene oxide is due mainly to the very slow formation of the epoxide and not to the consecutive oxidation to water and carbon dioxide.
69 citations
TL;DR: In this article, it was shown that Ag/CaCO3 catalysts exhibit a clear maximum in selectivity towards propene epoxide formation with increasing loading of potassium promoter, and this behavior correlates with changes in silver particle size distribution as revealed by HREM and XPS.
Abstract: With increasing loading of potassium promoter, Ag/CaCO3 catalysts exhibit a clear maximum in selectivity towards propene epoxide formation. This behavior correlates with changes in silver particle size distribution as revealed by HREM and XPS. Maximum selectivity and activity are achieved when the catalyst contains a large proportion of Ag particles whose size lies in the intermediate range 20-40 nm. Ag particles that are either much smaller or much larger than this are less selective towards epoxidation. The mechanistic implications of these findings are discussed and comparison is made with the corresponding properties of Ag/α-alumina catalysts normally used for ethene epoxidation.
69 citations
TL;DR: The autoreduction of palladium-platinum-containing titanium silicalite leads to an effective catalyst for the epoxidation of propylene to propylene oxide by O2 in the presence of H2.
Abstract: The autoreduction of palladium–platinum-containing titanium silicalite leads to an effective catalyst for the epoxidation of propylene to propylene oxide by O2 in the presence of H2. The “one-pot” reaction is favoured compared to the two-step reaction path.
63 citations