Study On Selective Hydrogenation Of Aromatic Esters With Manganese Oxide Film Catalyst

Aromatic aldehydes are widely used as building blocks for synthesis of organic fine chemicals, such as Pharmaceuticals, agrochemicals or perfumes. The conventional synthetical methods have several disadvantages, such as low yield, undesirable by-products and large amounts of wastes, so that a novel direct process using a heterogeneous catalyst for producing aldehydes with high yields and covering a wide range of products has been long awaited. In this article, transition-metal-oxides film was used as the catalysts for the direct hydrogenation of aromatic esters to the corresponding aldehydes under atmospheric pressure.In this article, the manganese oxide film was prepared by chemistry gas deposition method and was charactered by X-ray, TEM and SEM. A process for synthesis of p-tert-butylbenzaldehyde by direct hydrogenation of methyl p-tert-butylbenzoate was studied. The hydrogenation reaction was carried out in a fixed-bed reactor at 350-450°C under atmospheric pressure and the manganese oxide film was used as the hydrogenation catalyst. The reaction temperature, LHSV of methyl p-tert-butylbenzoate and GHSV of H₂ were examined. The optimal reactive conditions were obtained as follow: the reaction temperature 380～400°C, LHSV of 5mL/h and GHSV of H₂ about 20mL/min. Under the conditions, the conversion of methyl p-tert-butylbenzoate is 91.6% and the selectivity of p-tert-butylbenzaldehyde is 85.2%. The stability of the manganese oxide film catalyst was still good after the hydrogenation reaction of 600 h.The MnO₂ supportedγ-Al₂O₃, ZnO, TiO₂, MgO, CaO and diatomaceous earth were prepared by precipitation method. For catalytic hydrogenation of methyl p-tert-butylbenzoate, these catalysts show definite activity and selectivity to p-tert-butylbenzaldehyde.The effect on catalytic hydrogenation of the substituted groups on the aromatic ring of aromatic ester was investigated under the optimal reactive conditions by the manganese oxide film as catalyst. The conclusion is made that the stronger the ability of offering electrons, the higher the catalytic activity.