Modification And Catalytic Performance Of Pd/Al₂O₃ Catalyst For Anthraquinone Hydrogenation

As a green environmental protection oxidant,hydrogen peroxide（H₂O₂）is often used in medical,dyeing,papermaking,military and environmental fields.Among them,the anthraquinone autoxidation（AO）process is the most common way of H₂O₂ production in industry.The hydrogenation section is a key step in anthraquinone process,Pd/γ-Al₂O₃ is the most used catalyst in anthraquinone hydrogenation reaction due to the high selectivity and low cost.However,there are also some disadvantages such as low dispersion and insufficient catalytic performance.In this work,Al₂O₃-x M supports doped with phosphorus or magnesium were prepared by sol-gel method（M represents P or Mg,x represents the doping amount of M,wt%）,The influence of support-modification on the anthraquinone hydrogenation reaction was investigated by using the Pd/Al₂O₃-x M catalysts,A series of characterization were used to investigate the physical and chemical properties of the supports and catalysts,the relationship between the structure and surface properties of the catalysts and catalytic performance were explored.First,the influence of the amount of P doping on the physical and chemical properties of Al₂O₃-x P supports and Pd/Al₂O₃-x P catalysts were investigated,and the anthraquinone hydrogenation activity of the catalysts were evaluated.The characterization results show that the phosphorus incorporation can improve the crystal transition temperature and enhance the thermal stability of the support,increase the amount of weak acid sites and reduce the amount of strong acid sites.After phosphorus incorporation,more P-OH bonds existed on the catalyst surface,which have a better anchoring effect on Pd,increases the Pd dispersion and provided more active sites.Catalytic performance evaluation show that the Pd/Al₂O₃-1P catalyst has the best catalytic performance,the hydrogenation efficiency could reach9.7 g/L,which is 1.38 times higher than that of the unmodified catalyst（7.0 g/L）,the selectivity of 2-ethylanthrahydroquinone also increase slightly.Pd/Al₂O₃-1P catalyst could still maintain high activity and selectivity after six cycles.Pd leaching and byproduct deposition are main factors for deactivation of Pd/Al₂O₃ catalyst during anthraquinone hydrogenation.Secondly,the influence of Mg doping and calcination temperature on the physicochemical properties of the supports,catalysts and anthraquinone hydrogenation performance of Pd/Al₂O₃-x Mg（Pd-loaded 0.3wt%）catalysts were investigated.The characterization results showed that the increasement of calcination temperature could increase the pore size of Al₂O₃-Mg supports and decrease the specific surface area and pore volume.Mg incorporation could also increase the alkalinity and reduce the acidity of the supports.The Al₂O₃-Mg support calcined at 950℃has moderate alkalinity sites and few strong acid sites.When the Mg content is 1 wt%,Pd/Al₂O₃-1Mg catalyst has the highest Pd dispersion and the smallest Pd particle size.The catalytic activity results show that the activity of anthraquinone hydrogenation reaction increases first and then decreases with the increase of magnesium content.Pd/Al₂O₃-1Mg catalyst with the calcination temperature of 950℃exhibits the highest catalytic performance,the hydrogenation efficiency reaches 7.1 g/L.