偏磷酸镁修饰钨铝复合氧化物载铂催化剂的稳定性研究

Study on stability of platinum supported on tungsten-aluminum composite oxide modified by magnesium metaphosphate

以γAl_(2)O_(3)作为载体的催化剂,用于含水或有水生成的催化过程时,均会发生再水合现象,从而导致催化剂结构发生变化,使催化剂产生不可逆失活。针对甘油氢解这一典型的含水和有水生成的反应,采用分步浸渍焙烧法制备偏磷酸镁修饰的钨铝复合氧化物载铂催化剂(Pt/xMg(PO_(3))_(2)/WO_(x)/Al_(2)O_(3)),考察修饰前后的WO_(x)/Al_(2)O_(3)(W/Al)载体的水热稳定性,并在固定床反应器上对Pt/xMg(PO_(3))_(2)/WO_(x)/Al_(2)O_(3)催化剂反应活性和稳定性进行评价。使用X线衍射(XRD)、NH_(3)程序升温脱附(NH_(3)TPD)、N_(2)物理吸附脱附、CO脉冲吸附等表征手段对制备的试样进行表征。实验结果表明,在经过长时间水热处理后W/Al中的γAl_(2)O_(3)转变为勃姆石,试样的比表面积、孔径、孔容、酸量变化较大。Mg(PO_(3))_(2)修饰后能够抑制W/Al载体在水热处理时发生相变,从而使Mg(PO_(3))_(2)修饰后的W/Al试样水热稳定性得到提高,同时能够改善Pt在水热处理条件下的分散度,保持了催化剂的催化活性和稳定性。

When the catalyst supported onγ-Al_(2)O_(3)is used in the catalytic process containing water or producing water,the hydration phenomenon will occur,resulting in the change of catalyst structure and irreversible deactivation of the catalyst.The catalyst of platinum supported on tungsten-aluminum composite oxide modified by magnesium metaphosphate(Pt/xMg(PO_(3))_(2)/WO_(x)/Al_(2)O_(3))was prepared by step impregnation and calcination.The as-prepared catalyst was used in the glycerol hydrogenolysis reaction which was the typical catalytic process containing water and producing water.The hydrothermal stability of WO_(x)/Al_(2)O_(3)(W/Al)support before and after modification was investigated.The activity and stability of Pt/xMg(PO_(3))_(2)/WO_(x)/Al_(2)O_(3)catalyst were evaluated in a fixed bed reactor.The samples were characterized by X-ray diffraction(XRD),NH_(3) temperature programmed desorption(NH_(3)-TPD),N_(2) physical adsorption desorption and CO pulse adsorption.The experimental results showed that after a long period of hydrothermal treatment,theγ-Al_(2)O_(3)in W/Al sample transformed into boehmite,and the specific surface area,pore size,pore volume and acid content of the sample changed greatly.Mg(PO_(3))_(2) could inhibit the phase transition of W/Al support during hydrothermal process,which improved the hydrothermal stability of W/Al sample modified by Mg(PO_(3))_(2).At the same time,the dispersion of Pt under hydrothermal conditions was improved,and the catalytic activity and stability of the catalyst were maintained.