Gas-phase propene epoxidation over coinage metal catalysts

Abstract

Propene oxide (PO) is a very important bulk chemical and is produced on a scale of about 7.5 million tons per year. In industry, PO is produced via multiple reaction steps in the liquid phase, using hazardous chlorine or costly organic hydroperoxides as oxidants. Accordingly, development of a simple and green process to produce PO has been desired. This paper presents an overview of one-step propene epoxidation in the gas phase over coinage metal catalysts with a mixture of O 2 and H 2 or with molecular O 2 alone as oxidant. Silver (Ag) and gold (Au) catalysts can catalyze propene epoxidation with a mixture of O 2 and H 2 , with high selectivity, whereas copper (Cu) catalysts cannot. In this reaction Au catalysts are much more active than Ag catalysts. All the coinage metals can catalyze propene epoxidation by molecular O 2 , but with selectivity usually below 60%. The valence states of Cu species and the sizes of Ag particles and Au particles are of crucial importance in PO synthesis.

One step-synthesis of highly dispersed iron species into silica for propylene epoxidation with dioxygen

“…The slight decrease of the E g values and the apparent impoverishment of the catalytic behavior higher selectivity values (around 90%) can be found in other related works in gas-phase conditions, such as Au/Ti-SiO 2 catalyst in H 2 /O 2 gas streams compositions, but in these catalysts lower propylene conversion are obtained [7,56,57]. On the other hand, the catalyst based on alkaline salts (K + or Na + ) doped iron silica require very powerful oxidizing agents, such as N 2 O (without the presence of H 2 in the gas stream), to achieve PO selectivities around 60% for propylene conversions below 10% [26,58].…”

“…These catalysts have been widely studied and nowadays the reaction mechanism for this active phase is well known, with the formation of hydroperoxo and peroxo species on the metal nanoparticles and their interaction with propylene molecules adsorbed on titanium sites [7] being responsible for the high selectivity towards PO.…”

Water-assisted oxygen activation during selective oxidation reactions

“…Polyurethane, polyether polyols, glycol ethers, and propylene glycols are just a few of the various compounds produced from PO [45]. The ideal process for PO production, which is analogous to ethylene epoxidation over silver catalysts, is the selective epoxidation of propylene with molecular O 2 : C 3 H 6 + ½O 2 !…”

“…Progress toward safer and sustainable PO production may be achieved by eliminating hydrogen peroxide in the HPPO process through in situ generation of the right oxygen-containing intermediates. With Au/TiO 2 being a known selective catalyst for direct H 2 O 2 synthesis from a mixture of O 2 /H 2 , Haruta et al confirmed the feasibility of in situ H 2 O 2 generation on gold nanoparticles deposited on Ti-containing supports for the selective epoxidation of propylene [34,45,49]. Although these results are promising, the primary remaining barriers are poor hydrogen efficiency due to hydrogen oxidation to water, and the potential explosion risk when working with H 2 /O 2 mixtures.…”

Theoretical Investigation on the Au-Anchor Site in Phosphate-Doped Au/Al₂O₃Catalysts

“…The bulk Au is inert and inactive, whereas the nanosized Au on select support shows high activities for many catalytic reactions [1,2]. The catalytic activities of the nanosized Au are numerous; e.g., CO oxidization below room temperature [1][2][3], water gas shift reaction [1,4], propylene epoxidation [1,5,6], selective oxidization of glucose [1,7], selective hydrogenation of unsaturated aldehyde [1,8], and one-pot synthesis of azobenzene from nitrobenzene [1,9], etc. [1] In the field of Au catalysts, many researchers are interested in hetero-junctions between Au and supports (metal oxides, polymers and zeolites) because the hetero-junction sites are regarded as active sites of Au catalysts [1,6,10].…”