Construction of 2-(2′-Hydroxy-5′-methylphenyl)benzotriazole over Pd/γ-Al2O3 by a Continuous Process

The synthesis of 2-(2′-hydroxy-5′-methylphenyl)benzotriazole from 2-nitro-2′-hydroxy-5′-methylazobenzene over Pd/γ-Al2O3 in a fixed-bed reactor was investigated. Pd/γ-Al2O3 catalysts were prepared by two methods and characterized by XRD, TEM, H2-TPR, and N2 adsorption–desorption. Employed in the above reaction, the palladium catalyst impregnated in hydrochloric acid exhibited much better catalytic performance than that impregnated in ammonia–water, which was possibly attributed to the better dispersion of palladium crystals on γ-Al2O3. This result demonstrated that the preparation process of the catalyst was very important. Furthermore, the reaction parameters were optimized. Under the optimized conditions (toluene, NAB/triethylamine molar ratio 1:2, 60 °C, 2.5 MPa hydrogen pressure, 0.23 h–1 liquid hourly space velocity), about 90% yield of 2-(2′-hydroxy-5′-methylphenyl)benzotriazole was obtained. Finally, the time on stream performance of the catalyst was evaluated, and the reaction could proceed effect...