Jiqing Lu

Epoxidation of propylene on NaCl-modified silver catalysts with air as the oxidant

Propylene epoxidation by air was carried out on nacl-modified silver (nacl/ag) catalysts, and the catalysts were characterized by x-ray diffraction (xrd) and x-ray photoelectron spectroscopy (xps). the effects of nacl loadings, propylene to oxygen ratio, and the reaction time on the catalytic performance were investigated. it was found that the addition of nacl to silver significantly increases the propylene oxide (po) selectivity. the po yield has a maximum when the nacl loading is about 10 wt.%. also 12.4% conversion of propylene and 31.6% selectivity to po are obtained on the nacl/ag (10 wt.%) catalyst at 350 degreesc, space velocity 1.8 x 10(4) h(-1) and c3h6:o-2 = 1:2. xps and xrd characterizations show that agcl formed on the silver catalyst was favorable to propylene epoxidation. a compound with highly oxidized ag ion was also found, which may be effective for the reaction. (c) 2002 elsevier science b.v. all rights reserved.

Epoxidation of Propylene over Ag-CuCl Catalysts Using Air as the Oxidant

Ag-CuCl catalysts were found to be active and selective for the epoxidation of propylene using air as the oxidant. Ag catalyst gives a propylene conversion of 31.6%, with a propylene oxide (PO) selectivity of 0.42% at a reaction temperature of 350 °C after 220 min of reaction. Addition of CuCl significantly improves the selectivity to PO, and suppresses the conversion of propylene. The Ag-CuCl (1/0.6) catalyst gives propylene conversion of about 3% and a PO selectivity of about 30% at a reaction temperature of 350 °C after 500 min of reaction. The activity of the Ag-CuCl catalyst increases with the reaction time and the selectivity to PO is very stable for this catalyst. It is found that AgCl and CuO phases formed during the catalyst preparation are beneficial to the epoxidation of propylene.

Epoxidation of olefins on M-SiO2 (M=Ti, Fe, V) catalysts with highly isolated transition metal ions prepared by ion beam implantation

M-SiO2 (M=Ti, V, Fe) catalysts with highly isolated transition metal ions were prepared by ion beam implantation and the catalysts were tested for the epoxidation of styrene, 1-octene and cyclohexene using dilute H2O2 (30%) as oxidant. Ti-SiO2 shows the highest epoxide selectivity, while Fe-SiO2 exhibits the highest activity among the three catalysts. Epoxide selectivity can approach 100% for the epoxidation of styrene on Ti-SiO2 catalyst at 298 K. The nature of active sites in the catalysts was significantly changed after the calcination. The activities and selectivities of the catalysts are mainly due to the isolated surface transition metal ions derived from the ion beam implantation. It is assumed that there are at least two types of active sites, M (α) (isolated Mn+) and M (β) (aggregated metal oxide nanoparticles) on the catalyst surface, and the good activity and selectivity are attributed mainly to the M (α) sites.

Direct gas-phase epoxidation of propylene to propylene oxide using air as oxidant on supported gold catalyst

Abstract Gold catalysts supported on SiO 2 , TiO 2 , TiO 2 -SiO 2 , and ZrO 2 -SiO 2 supports were prepared by impregnating each support with a basic solution of tetrachloroauric acid. X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) techniques were used to characterize their structure and surface composition. The results indicated that the size of gold particles could be controlled to below 10 nm by this method of preparation. Washing gold catalysts with water could markedly enhance the dispersion of metallic gold particles on the surface, but it could not completely remove the chloride ions left on the surface. The catalytic performance of direct vapor-phase epoxidation of propylene using air as an oxidant over these catalysts was evaluated at atmospheric pressure. The selectivity to propylene oxide (PO) was found to vary with reaction time on the stream. At the reaction conditions of atmosphere pressure, temperature 325° C, feed gas ratio V (C 3 H 6 )/ V (O 2 )= ½, and GHSV = 6000 h −1 , 17.9% PO selectivity with 0.9% propylene conversion were obtained at initial 10 min for Au/SiO 2 catalyst. After reacting 60 min only 8.9% PO selectivity were detected, but the propylene conversion rises to 1.4% and the main product is transferred to acrolein (72% selectivity). Washing Au/TiO 2 -SiO 2 and Au/ZrO 2 -SiO 2 samples with magnesium citrate solution could markedly enhance the activity and PO selectivity because smaller gold particles were obtained.

Epoxidation of cyclohexene on Ti/SiO2 catalysts prepared by chemical grafting TiCl4 on deboronated silica xerogel

Abstract Ti/SiO 2 (or Ti/de[B]SiO 2 ) catalysts were prepared by grafting deboronated silica xerogel with gaseous TiCl 4 . Using TBHP as oxidant, the Ti/de[B]SiO 2 catalyst shows both catalytic activity and selectivity in epoxidation of cyclohexene better than 80%, and the activity can be comparable with that of Ti-β. The catalytic activity of Ti/de[B]SiO 2 strongly depends on the content of B of support precursor, and the pretreatment temperature of the support. IR studies show that the sites in the deboronated silica xerogel to react with TiCl 4 are not only the silanol nests, but also the defect sites produced during the deboronation.