Zn对Ni/SiO_(2)催化剂苯甲醚氢脱氧性能的影响

Effect of Zn on performance of Ni/SiO_(2)for hydrodeoxygenation of anisole

采用等体积浸渍法制备了Ni/SiO_(2)及NixZn/SiO_(2)(x代表Ni/Zn原子比)催化剂,在常压固定床反应器上考察了催化剂苯甲醚气相加氢脱氧性能。研究发现,经550℃还原后NixZn/SiO_(2)中形成了Ni-Zn合金,当Ni/Zn原子比为30时可获得较小合金晶粒尺寸和较高H2化学吸附量。在苯甲醚加氢脱氧反应中,Ni-Zn合金的形成有利于苯甲醚直接脱氧形成苯,同时抑制了CO甲烷化及C-C键氢解,这是因为形成合金后亲氧性金属Zn对Ni的几何隔离作用。Ni_(30)Zn/SiO_(2)催化剂的活性和苯选择性均高于Ni/SiO_(2)。结果表明,Ni_(30)Zn/SiO_(2)催化剂失活与产物水氧化Ni-Zn合金表面及积炭有关。

Herein,SiO_(2) supported metallic Ni(Ni/SiO_(2)) and bimetallic Ni-Zn(NixZn/SiO_(2))(x represents the Ni/Zn atomic ratio)catalysts were prepared by the incipient wetness impregnation method and their activities were tested in vapor phase hydrodeoxygenation(HDO)of anisole under 0.1 MPa.The characterization results show that Ni-Zn alloy forms in NixZn/SiO_(2) after reduction at 550℃,and a suitable Ni/Zn atomic ratio(30)leads to smaller alloy particle size and consequently more H2 adsorption amount than others.In the HDO reaction,the formation of Ni-Zn alloy facilitates the direct deoxygenation pathway and suppresses CO methanation and C-C bond hydrogenolysis,which is ascribed to the isolation effect of the Ni atoms by the oxophilic Zn ones.Ni_(30)Zn/SiO_(2) gives not only higher anisole conversion but also higher selectivity to benzene than Ni/SiO_(2).Therefore,the introduction of a suitable amount of oxophilic Zn in Ni/SiO_(2) promotes the HDO of anisole to benzene.Finally,we propose that the Ni_(30)Zn/SiO_(2) deactivation is related to the oxidation of Ni-Zn alloy and carbon deposition on the catalyst surface.