Gas-Phase Propylene Epoxidation

2 Gas-Phase Propylene Epoxidation with Hydrogen-Oxygen Mixtures on Au/Ti02 

Reaction pathways for propylene epoxidation over Au/Ti02 Sellers predicted that theoretically, on gold, H202 can be produced from 02 and H2 [132]. Later, Haruta and 

Although Au particles with mean diameters around 5-6 nm were observed by transmission electron microscopy (TEM), Delgass suggested, based on DFTcalculations, that small Au clusters such as Au3 rather than the large particles are responsible 

Improvement of Au/3-D mesoporous Ti-Si02 As for propylene epoxidation, alkaline or alkaline earth metal chlorides were efficient solid-phase promoters however, chloride anion markedly enhanced the coagulation of Au particles [147]. For Au/3D Ti-Si02, Ba(N03)2 was the best solid-phase promoter, which might be transformed into BaO after calcination at 573 K and might function by neutralizing acid sites on 

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Figure 24. Size of metal particles and support pores in silver and gold catalysts for gas-phase propylene epoxidation.

Because the petrochemical industry is based on hydrocarbons, especially alkenes, the selective oxidation of hydrocarbons to produce organic oxygenates occupies about 20% of total sales of current chemical industries. This is the second largest market after polymerization, which occupies about a 45% share. Selectively oxidized products, such as epoxides, ketones, aldehydes, alcohols and acids, are widely used to produce plastics, detergents, paints, cosmetics, and so on. Since it was found that supported Au catalysts can effectively catalyze gas-phase propylene epoxidation [121], the catalytic performance of Au catalysts in various selective oxidation reactions has been investigated extensively. In this section we focus mainly on the gas-phase selective oxidation of organic compounds. 

B. Chowdhury, J. J. Bravo-Suarez, N. Mimura, J. Q. Lu, K. K. Bando, S. Tsubota, M. Haruta, In situ UV-vis and EPR study on the formation of hydroperoxide species during direct gas phase propylene epoxidation over Au/Ti-SiO2 catalyst, /. Phys. Chem. B 110 (2006) 22995. 

In supported gold catalysts for the gas-phase propylene epoxidation, two hypotheses are competing. One assumes that gold clusters inside the cages of TS-1 (crystalline microporous titanium silicates) may act as the working... 

C. Wang, X. Guo, X. Wang, R. Wang, J. Hao, Gas-phase propylene epoxidation over Ag/TS-1 prepared in W/O microemulsion Effects of the molar ratio of water to surfactant and the reaction temperature, Catal. Lett. 96 (2004) 79. 

While industry has selected liquid-phase H202-based technology for imminent PO plants [11], due to handling issues and cost associated with making H2O2, a direct gas-phase propylene epoxidation process, analogous to the commercial ethylene oxide (EO) process [19,20], has long been desired [21]. While ethylene... 

While MCM-41- and 48-based materials dominate as the primary mesoporous materials explored for gas-phase propylene epoxidation, a recent article examines the reactivity of Au deposited on Ti-TUD containing 3 mol% Ti [57]. Ti-TUD consists of a sponge-like structure with an average pore size of about 13 run. Although the specific surface area of this material is less than that of MCM-41 or MCM-48, the larger pore system allowed for essentially all of the deposited Au to have access to the pore system. A maximum rate of 53.7 gpo kgcat 470 °C... 

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