载Ni沸石上Ni(Ⅱ)的还原作用Ⅸ.Ni/DAIM催化剂催化二甲苯转化

REDUCTION OF Ni(Ⅱ) IONS ON Ni-CONTAINING ZEOLITES Ⅸ.THE CONVERSION OF XYLENE OVER Ni/DAIM

本文进一步考察了载Ni丝光沸石的SiO_2/Al_2O_3比对二甲苯转化和产物分布的影响.结果表明,无论是载Ni或不载Ni丝光沸石上,邻二甲苯转化率随SiO_2/Al_2O_3增加而增加,SiO_2/Al_2O_3<20时,转化率明显增加,SiO_2/Al_2O_3>20时,递增缓慢,并趋于稳定.丝光沸石载Ni后,于氮气氛中进行二甲苯转化反应,总转化率降低,异构化产率基本不变,歧化产率略有降低,脱甲基化产率接近于零.表明浸渍Ni^(2+)形态对脱甲基化有抑制作用,Ni不是歧化反应的活性中心.在临氢条件下,Ni^0也没有抑制歧化反应的作用,Ni含量增加,二甲苯异构化产率基本不变.

The effect of loading of Ni and SiO_2/Al_2O_3 ratio of mordenite zeolites on conversion of xylene and it's product distributions were further investigated.The results showed that for Ni loaded or unloaded mordenites ,the conversion of xylene increases with the increase of Si0_2/Al_2O_3 ratios with SiO_2/Al_2O_3<20,the conversion of xylene increases obviously; with SiO_2/Al_2O_3>20, the conversion of xylene increases slowly and tendes to level off. After loading of Ni on mordenite and under N_2 atmosphere, the conversion of xylene is reduced with little changes in selectivity of isomerization or disproportionation, and the dealkylation of xylene is minimal. It showed that the impregnated Ni^(2+) inhibites the dealkylation of alkylbenzene. Ni is not the active site for disproportionation. Under H_2 atmosphere, Ni does not inhibit disproportionation. No change in selectivity of isomerization of xylene was observed with increasing Ni content.