A novel catalyst, MgFe 2O 4, for hydroxylation of phenol with hydrogen peroxide was synthesized via coprecipitation method from an aqueous solution containing Fe(NO 3) 3·9H 2O and Mg(NO 3) 2·6H 2O with ammon...A novel catalyst, MgFe 2O 4, for hydroxylation of phenol with hydrogen peroxide was synthesized via coprecipitation method from an aqueous solution containing Fe(NO 3) 3·9H 2O and Mg(NO 3) 2·6H 2O with ammonia. The X ray diffraction peaks of the catalyst show that the as prepared sample has engendered MgFe 2O 4 crystal with spinel structure, which is also confirmed by its IR spectrum. In the hydroxylation of phenol with hydrogen peroxide, MgFe 2O 4 catalyst exhibited high activity after a short induction period. In particular, the addition of a little amount of acetic acid in the reaction liquid can effectively shorten the induction period. Under the same reaction conditions, the diphenol selectivity over MgFe 2O 4 is higher than that over TS 1, furthermore, the reaction time is shortened greatly. The experimental phenomena can be explained by the free radical mechanism.展开更多
Influence of OH -/SiO 2 ratio (alkalinity) on the particle size distribution and structure of the β zeolite synthesized during a shorter crystallization period (60 h) has been studied. The results indicate that the c...Influence of OH -/SiO 2 ratio (alkalinity) on the particle size distribution and structure of the β zeolite synthesized during a shorter crystallization period (60 h) has been studied. The results indicate that the characteristic point of crystallinity of synthetic zeolite is at alkalinity of 0 23～0 24. When the alkalinity is higher than 0 39, β zeolite can not be obtained. The difference of crystal size between the zeolites synthesized from gels with different alkalinity is 0 7～0 8 μm. Along with the increase of the alkalinity, the particle size distribution varies from narrow to wide and again from wide to narrow, and the framework Si/Al ratio by 29 Si NMR increases gradually and then decreases, but the change of OhAl/TdAl ratio by 27 Al NMR is contrary to that of framework Si/Al ratio. In addition, the Si(OH) site existing in the TEA β is confirmed by NMR.展开更多
The mordenite membrane was prepared on a α-Al 2O 3 tube by in situ hydrothermal synthesis. The crystallization was carried out at 443 K for 2～4 days. Silica sol and sodium aluminate were used as the sources of silic...The mordenite membrane was prepared on a α-Al 2O 3 tube by in situ hydrothermal synthesis. The crystallization was carried out at 443 K for 2～4 days. Silica sol and sodium aluminate were used as the sources of silica and alumina, respectively, and tetraethylammonium bromide (TEABr) as the template. The molar composition of the parent solution was 11 4Na 2O∶1 0Al 2O 3∶40SiO 2∶2500H 2O∶1 5TEABr. SEM and XRD were used to characterize the powder product and the composite membrane. The synthesized mordenite membrane proved to be in a full coverage and an excellent intergrowth. The mordenite crystals were about 20～30 μm and the thickness of the mordenite membrane was 30～40 μm. Based on the SEM pictures of the membrane in the early stage of hydrothermal synthesis, a growth model for the mordenite membrane was assumed. At first a gel layer was formed on the surface of the alumina tube. Nucleation took place in the gel layer but not at the interface of the gel layer and bulk solution. The gel layer provided the nutrients for the growth of zeolite crystals. After the gel layer was consumed completely, the zeolite crystals or membrane were exposed to the bulk solution. The membrane separation test on the mordenite membrane showed that the permeances of pure H 2 and N 2 at 298 K were 6 92×10 -7 and 1 81×10 -7 mol/(m 2·s·Pa), respectively. The ideal selectivity of H 2/N 2 was 3 82, which is higher than that of Knudsen mechanism. It suggested that the mordenite membrane had the ability of molecular sieving.展开更多
文摘A novel catalyst, MgFe 2O 4, for hydroxylation of phenol with hydrogen peroxide was synthesized via coprecipitation method from an aqueous solution containing Fe(NO 3) 3·9H 2O and Mg(NO 3) 2·6H 2O with ammonia. The X ray diffraction peaks of the catalyst show that the as prepared sample has engendered MgFe 2O 4 crystal with spinel structure, which is also confirmed by its IR spectrum. In the hydroxylation of phenol with hydrogen peroxide, MgFe 2O 4 catalyst exhibited high activity after a short induction period. In particular, the addition of a little amount of acetic acid in the reaction liquid can effectively shorten the induction period. Under the same reaction conditions, the diphenol selectivity over MgFe 2O 4 is higher than that over TS 1, furthermore, the reaction time is shortened greatly. The experimental phenomena can be explained by the free radical mechanism.
文摘Influence of OH -/SiO 2 ratio (alkalinity) on the particle size distribution and structure of the β zeolite synthesized during a shorter crystallization period (60 h) has been studied. The results indicate that the characteristic point of crystallinity of synthetic zeolite is at alkalinity of 0 23～0 24. When the alkalinity is higher than 0 39, β zeolite can not be obtained. The difference of crystal size between the zeolites synthesized from gels with different alkalinity is 0 7～0 8 μm. Along with the increase of the alkalinity, the particle size distribution varies from narrow to wide and again from wide to narrow, and the framework Si/Al ratio by 29 Si NMR increases gradually and then decreases, but the change of OhAl/TdAl ratio by 27 Al NMR is contrary to that of framework Si/Al ratio. In addition, the Si(OH) site existing in the TEA β is confirmed by NMR.
文摘The mordenite membrane was prepared on a α-Al 2O 3 tube by in situ hydrothermal synthesis. The crystallization was carried out at 443 K for 2～4 days. Silica sol and sodium aluminate were used as the sources of silica and alumina, respectively, and tetraethylammonium bromide (TEABr) as the template. The molar composition of the parent solution was 11 4Na 2O∶1 0Al 2O 3∶40SiO 2∶2500H 2O∶1 5TEABr. SEM and XRD were used to characterize the powder product and the composite membrane. The synthesized mordenite membrane proved to be in a full coverage and an excellent intergrowth. The mordenite crystals were about 20～30 μm and the thickness of the mordenite membrane was 30～40 μm. Based on the SEM pictures of the membrane in the early stage of hydrothermal synthesis, a growth model for the mordenite membrane was assumed. At first a gel layer was formed on the surface of the alumina tube. Nucleation took place in the gel layer but not at the interface of the gel layer and bulk solution. The gel layer provided the nutrients for the growth of zeolite crystals. After the gel layer was consumed completely, the zeolite crystals or membrane were exposed to the bulk solution. The membrane separation test on the mordenite membrane showed that the permeances of pure H 2 and N 2 at 298 K were 6 92×10 -7 and 1 81×10 -7 mol/(m 2·s·Pa), respectively. The ideal selectivity of H 2/N 2 was 3 82, which is higher than that of Knudsen mechanism. It suggested that the mordenite membrane had the ability of molecular sieving.
