N-hydroxyphthalimide And Its Derivative Incorporated Onto Cu-BTC For Liquid-phase Oxidation Of Toluene

The major products of toluene oxidation including benzaldehyde, benzyle clcohol and benzoic acid are widely used to synthesize a diversity of useful chemicals, such as pharmaceuticals, dyestuff, perfume, foodstuff, preservatives and rubber auxiliary agents. Specially, benzaldehyde and benzyle clcohol existed domestic supply gap with the requirement increasing year by year. What’s more, the oxidation of toluene is carried out under severe conditions in SNIA caprolactam commercial production processes and benzoic acid is the major final product. Therefore, developping new toluene oxidation catalytic system under mild conditions through new catalytic materials for high selectivity of benzaldehyde and benzyle alcohol has attracted much attention. In this paper, Cu-BTC, which is one of the classic metal organic frameworks, was chosen as carrier for its high metal content, larger surface area, good thermal stability, fine structure stability and unsaturated metal-binding sites. N-hydroxyphthalimide(NHPI) and its derivative were incorporated onto Cu-BTC by impregnation method with only one step to construct newly complex catalyst. This work was aimed at improving the selectivity of benzaldehyde and benzyle alcohol with higher toluene conversion under solvent-free condition, and solving the problem of catalyst recovery at the same time.Firstly, two metal organic frameworks of Cu-BTC-A and Cu-BTC-B were prepared by solvothermal method at 140℃ and 100℃, respectively. The structure of prepared Cu-BTC samples was characterized by XRD, SEM, EA, ICP, TG, FT-IR and nitrogen adsorption. The results showed that the prepared Cu-BTC-A and Cu-BTC-B samples were all 3D frameworks with high surface area of 766 m2g-1 and 1404 m2g-1, respectively. Also, both two samples had good thermal stability that can keep structure stable before 303℃.Secondly, through impregnation method, N-hydroxyphthalimide(NHPI) was incorporated onto Cu-BTC samples by using mixed solution of dichloromethane and methanol or tetrahydrofuran as solvents to synthesize NHPI/Cu-BTC catalysts. All prepared catalysts were characterized by XRD, SEM and XPS. The results showed that after incorporation of NHPI, the surface area of Cu-BTC samples sharply decreased(<35 m2g-1 in all NHPI/Cu-BTC catalysts), which was a significant evidence for the internal location of NHPI inside the carrier Cu-BTC. Further, the synthesized NHPI/Cu-BTC catalysts were used as heterogenous catalysts for oxidation of toluene and the recovery property of catalysts were investigated. The results showed that the toluene conversion was 7.7% with the selectivity of benzaldehyde and benzyle clcohol more than 50% at 110℃ for 2 h in the presence of 1% mol NHPI/Cu-BTC as catalyst under solvent-free condition without metal compounds co-catalyst. However, the reaction activity of reused catalyst obviously decreased.Thirdly, the relativity between the surface area of catalyst and reaction activity were investigated. The ordination forms between active component and carrier were also studied. It was found that the surface area of catalyst and reaction activity were irrelevant, besides, the interactions between active component and carrier were adsorption affinity.Finally, N’N-dihydroxypyromellitimide(NDHPI), which was derivative of NHPI, was incorporated onto Cu-BTC-A by impregnation method to obtain NDHPI/Cu-BTC-A catalysts. The synthesized catalysts were characterized by XRD, TG, FT-IR and the catalytic performance for liquid-phase oxidation of toluene was investigated. After incorporation of NDHPI, the surface area of Cu-BTC-A from 776 decreased to 27 m2g-1, which was a significant evidence for the internal location of NDHPI inside the carrier Cu-BTC. The oxidation reaction takes place with more than 70% selectivity of benzaldehyde and benzyle clcohol and 2.8% conversion at 110℃ for 5 h used 1% mol NDHPI/Cu-BTC-A as catalyst under solvent-free condition without metal compounds co-catalyst. Under the same conditions, NDHPI was not superior to NHPI as an active component in the composite catalyst.