Formid Acid Decomposition For Hydrogen Generation And Catalytic Transfer Hydrogenation

There is 4.4 wt% hydrogen in the molecule of formic acid, which is commonly known as a hydrogen source. In the presence of a suitable catalyst, formic acid can decompose into H2 and CO2 at ambient temperature and pressure. Compared with high-pressure hydrogen, formic acid has great advantages in terms of security because it is liquid at ambient temperature and convenient for store and transportation. Formic acid is widely used in catalytic transfer hydrogenation(CTH), such as the reduction of compounds containing carbonyl and nitro groups, due to its good reduction selectivity and mild conditions for decomposition and post-treatment.In this paper, Pd/AC catalyst was prepared by impregnation method using PdCl2 as palladium source. The catalyst was characterized by N2 isothermal adsorption–desorption, TPR, XRD and TEM. The results showed that the size of Pd particles increased gradually with increasing of Pd loading, and particle agglomeration appeared. When 5wt% Pd/AC catalyst was used to catalyze formic acid decomposition, formic acid conversion was 97.8% with 99.4% H2 selectivity under reaction conditions as following: concentration of formic acid of 0.1 mol/L, a catalyst-to-aqueous formic acid ratio of 0.010 g/mL, 100℃ and 1 h. The decrease of the catalytic activity was not obvious when the catalyst was recycled for the first time. But when it was reused for 5 times, formic acid conversion was decreased to 88.6%, while H2 selectivity remained as high as that over fresh catalyst(>99%). It was found that the cause for the deactivation of Pd/AC catalyst was Pd leaking.Using formic acid as hydrogen source, CTH of benzene and phenol were studied respectively over Pd/AC catalyst. For benzene CTH, both the conversion and selectivity to cyclohexene were very low. The poor activity may be assigned to the low pressure H2 that was provided by formic acid decomposition. In addition, cyclohexane, the deep hydrogenation product of benzene was obtained more easily over Pd catalyst. As for the phenol CTH, 65.3% phenol conversion with 96.2% cyclohexanone selectivity were obtained under optimal conditions. In other words, 400 μL of formic acid was introduced into 10 mL of 0.25 mol/L phenol aqueous solution in a N2 environment of 0.3 MPa, with a catalyst-to-aqueous phenol ratio of 0.05 g/mL, then the reaction was conducted at 70℃ for 4 h. When using AC with large specific surface area(908.5 m2/g) as support, Pd particles were dispersed highly on the surface of AC. When the catalyst was applied in the phenol CTH, phenol was converted completely with 57.6% cyclohexanone.