改性Mo_2C/Al_2O_3催化剂用于甲烷部分氧化制合成气

Study on Modified Mo_2C/Al_2O_3 Catalyst for POM to Syngas

制备了含有少量Ni,Co ,Cu或K的Mo2 C/Al2 O3 催化剂 ,用于甲烷部分氧化 (POM)制合成气反应 ,并用程序升温表面反应 (TPSR)进行了表征 .Ni可以促进氧化钼被氢还原 ,进而促进氧化钼的碳化及甲烷的活化 ,故Ni改性催化剂具有很高的催化活性和选择性 ,并且有很高的催化稳定性 .Co也可以促进氧化钼的碳化及甲烷的活化 ,故Co改性催化剂也具有较高的催化活性和稳定性 .Cu的添加有利于氧化钼的碳化及甲烷的活化 ,故Cu改性催化剂在开始阶段表现出对甲烷转化的促进作用 ,但随后其促进作用消失 ,与Cu的存在状态发生变化有关 ;Cu改性催化剂具有较低的选择性 ,则与其促进氧的活化作用有关 .K的添加不利于氧化钼的碳化及甲烷的活化 ,故K改性催化剂的催化活性和选择性较低 .

The supported Mo 2C/Al 2O 3 catalyst was prepared and modified by a trace amount of Ni, Co, Cu or K, and evaluated under the conditions of n(CH 4)/ n(O 2)=2.05, GHSV=20.5 L/(g·h) and θ=850 ℃ in a microreactor for partial oxidation of methane (POM) to syngas. The results showed that the Ni-Mo 2C/Al 2O 3 exhibited the highest activity and selectivity, and its catalytic performance was particularly stable. Co had the functions, though to less extent, similar to Ni. The addition of Cu promoted the CH 4 conversion at initial stage, but then the promotion disappeared rapidly. However, the addition of Cu was unfavorable to the selectivity for CO and H 2. The addition of K was unfavorable to POM to syngas. The catalytst samples were characterized by temperature-programmed surface reaction (TPSR) technique. The TPSR result indicated that the carbonization of MoO 3 was carried out via two steps, namely, reduction by H 2 at first and then carbonization by CH 4. The addition of Ni or Co promoted the activation of CH 4, the reduction of MoO 3 by H 2 and the deposition of carbon, and then promoted the carbonization. Thus, there was possibility for the modified catalyst to hold more carbide or oxycarbide as active phase in the process of POM. Whilst for K-modified catalyst, the K prevented the catalyst from reduction by H 2, carburization by CH 4 and activation of CH 4. Thus, the K was unfavorable to POM. As for Cu-modified catalyst, Cu promoted the reduction of MoO 3 and activation of CH 4, thus promoted POM to syngas. Meanwhile, the Cu was favorable to the activation of O 2 molecule, being unfavorable to the reaction selectivity. For the Cu-modified catalyst, the disappearance of promotion to CH 4 conversion after initial period might be due to the change of valence state of Cu ion.