Selective Vapor-Phase Epoxidation of Propylene over Au/TiO2Catalysts in the Presence of Oxygen and Hydrogen

Hayashi, Toshio; Tanaka, Koji; Haruta, Masatake

doi:10.1006/jcat.1998.2157

Cited by 1,131 publications

(904 citation statements)

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“…5 The original application of catalysts based on gold nanoparticles was low temperature CO oxidation. 6 Since that time, these catalysts have received a considerable amount of attention, resulting in about 100 publications until now.…”

Section: Introductionmentioning

confidence: 99%

Mechanistic Study into the Direct Epoxidation of Propene over Gold/Titania Catalysts

2005

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The epoxidation of propene over gold/titania based catalysts was investigated using different techniques. Infrared spectroscopic information showed that one key step in the reaction mechanism is a reaction catalyzed by gold between titania surface groups and propene. In this reaction step, a bidentate propoxy species is formed on titania. This species adsorbs strongly on the catalyst, and it is the same species which is formed when propene oxide adsorbs on titania. Gravimetrical adsorption experiments and catalytic tests show that product adsorption and desorption are important factors determining the catalytic activity and the catalyst stability. By combining the information from different techniques, a kinetic mechanism is proposed.

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Section: Introductionmentioning

confidence: 99%

Mechanistic Study into the Direct Epoxidation of Propene over Gold/Titania Catalysts

2005

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“…1 the yield of the epoxide is not high (~5%). 4 This work hints at the possibility that there is a optimal cluster size for the efficient and selective oxidation of alkenes.…”

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confidence: 97%

“…1 Since then, supported gold catalysts have been used for the selective epoxidation/oxidation of various alkenes such as styrene, 15 cyclohexene, cis-cyclooctene and trans-stilbene. [2][3][4][5][6][7] A major current challenge is to use O 2 as a green oxidant.…”

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confidence: 99%

“…Oxidation of styrene (1) in toluene at 80 C using anhydrous TBHP as an oxidant yielded styrene oxide (2) as a major product in every case, whereas acetophenon (3), benzaldehyde (4), benzylalcohol (5), and benzoic acid (6) were also produced. ‡ 14 It was essential to use toluene as a 60 solvent to obtain 2 in a high yield, in sharp contrast to the case of Au/graphite 3 and Au/SiO 2 .…”

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Efficient and selective epoxidation of styrene with TBHP catalyzed by Au25clusters on hydroxyapatite

et al. 2010

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Au 25 clusters supported on hydroxyapatite oxidized styrene in toluene with 100% conversion and 92% selectivity to the epoxide, under optimum conditions and using anhydrous tert-butyl hydroperoxide (TBHP) as an oxidant. 10In 1998, Haruta and coworkers demonstrated for the first time that supported Au nanoparticles (AuNPs) are effective for the direct epoxidation of propene using molecular oxygen. 1 the yield of the epoxide is not high (~5%). 4 This work hints at the possibility that there is a optimal cluster size for the efficient and selective oxidation of alkenes. Here we focus on the epoxidation of styrene and aim to systematically study the effect on the catalytic activity of the size of Au clusters that 25 are immobilized on hydroxyapatite (HAP; Ca 10 (PO 4 ) 6 (OH) 2 ). 8 We use tert-butyl hydroperoxide (TBHP) as an oxidant since it is known to be more effective than O 2 for alkene oxidations. [5][6][7] We describe the synthesis of HAP-supported Au 25 clusters; they show a higher catalytic performance 30 (100% conversion and 92% selectivity to the epoxide) than larger analogs.The preparation of HAP-supported Au 25 catalysts is depicted in Scheme 1. The basic idea is to use as a precursor ligand-protected Au clusters with a well-defined core size. 4 18 clusters were found to be adsorbed completely on HAP as evidenced by the colorless filtrate (ESI, † Fig. S1). The Au loading of the composites thus obtained is 0.5 wt% (ESI, † Table S1), so the composite is Fig. S3). The diameter of the Au core is comparable to that of Au 25 (~0.9 nm), assuming a spherical shape. 80The 0.5Au 25 :SG-HAP composite was then incubated for removal of the thiolate ligands.The results of thermogravimetric analysis revealed a 49% weight loss of Au 25 (SG) 18 after calcination at 300 C in vacuo for 2 h (ESI, † Fig. S4); this weight corresponded to the calculated weight of 85 the GS ligands in Au 25 (SG) 18 (53%). Thus, 0.5Au 25 :SG-HAP was calcined under the above mentioned conditions to remove the GS ligands. This removal was confirmed by inductively coupled plasma (ICP) measurements. After calcination, the sulfur content reduced from 0.058 wt% to 0.005 wt%, which 90 was comparable to the amount of sulfur impurity in HAP. An HAADF-STEM image of the resulting Au 25 -HAP shows that most of the clusters are 1.2-1.5 nm in size (Fig. 1A).

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“…The H 2 O 2 then transfers to Ti tetrahedral sites to form Ti-OOH species active for selective oxidations, such as propylene epoxidation. 13,14 In the case of propane, a similar mechanism may take place, and the involvement of isopropoxy intermediate species could explain the formation of acetone and isopropanol.…”

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confidence: 97%

Propane reacts with O2 and H2 on gold supported TS-1 to form oxygenates with high selectivity

et al. 2008

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Selective Vapor-Phase Epoxidation of Propylene over Au/TiO2Catalysts in the Presence of Oxygen and Hydrogen

Cited by 1,131 publications

References 38 publications

Mechanistic Study into the Direct Epoxidation of Propene over Gold/Titania Catalysts

Mechanistic Study into the Direct Epoxidation of Propene over Gold/Titania Catalysts

Efficient and selective epoxidation of styrene with TBHP catalyzed by Au25clusters on hydroxyapatite

Propane reacts with O2 and H2 on gold supported TS-1 to form oxygenates with high selectivity

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