V_2O_5K_2SO_4/CFG对甲苯选择氧化的催化性能及表征

CATALYTIC PERFORMANCE AND CHARACTERIZATION OF V_2O_5K_2SO_4/CFG FOR SELECTIVE OXIDATION OF TOLUENE

用浸渍法制备了 V2 O5 K2 SO4/ CFG催化剂 ,并用于甲苯选择氧化生成苯甲醛反应。当 V2 O5 和 K2 SO4的重量比为 1∶ 1 ,V2 O5 的负载量为 1 0 %～ 1 2 % ( w)时 ,催化剂的活性最高 ,此时甲苯转化率为 1 1 .98% ,苯甲醛选择性为 93 .0 9%。以 K2 SO4为助催化剂明显优于 Sn O2 和 Ag2 O。 XRD结果说明 ,添加 K2 SO4有利于 V2 O5在 CFG上均匀分散。50 0℃焙烧时 ,有一部分 K2 SO4分解生成 K2 O,它能中和 V2 O5 和 CFG表面上的酸性位 ,使产物易于脱附 ,抑制了副反应 ,增加了生成苯甲醛的选择性。 V2 O5 K2 SO4/ CFG的比表面为 2 8.0 9m2 / g,孔分布为单孔型 ,平均孔径为 2 0 .0 9nm。ESR分析表明 ,在反应过程中有中间体 V4+ 生成 ,是典型的还原氧化机理。

V 2O 5K 2SO 4/CFG catalyst was prepared by impregnation method and it was used as the catalyst of selective oxidation reaction of toluene for benzaldehyde. The activity of the catalyst was the heighest when a ratio of V 2O 5 to K 2SO 4 (weight) was 1∶1 and loading amount of V 2O 5 was 10%～12%(w). The conversion of toluene and the selectivity of benzaldehyde were respectively 11.98%(mol) and 93.09%(mol). K 2SO 4 was obviously superior to SnO 2 and AgO 2 as the promoter of V 2O 5. XRD results showed that K 2SO 4 could promote V 2O 5 uniform dispersion on the CFG. A part of K 2SO 4 was decomposed into K 2O when the catalyst was calcined at 500 ℃. K 2O could neutralize acidic sites on the V 2O 5 and CFG and depress side reactions and increased the selectivity of benzaldehyde. The surface area of V 2O 5K 2SO 4/CFG was 28.09 m 2/g and pore size distribution showed shapes and average pore diameter was 20.09 nm. ESR analyses denote V 4+ in termediate was formed in reation and it was a typical redox mechanism.