甲苯氨氧化合成苯甲腈VPO催化剂研究

Ammoxidation of Toluene to Benzonitrile on VPO Catalysts

用浸渍法制备了不同磷钒比(P/V)的VPO和VPO/硅胶催化剂,并用XRD、FTIR、TPR进行了表征,在甲苯氨氧化制苯甲腈反应中考察了其催化性能。发现P的引入破坏了V2O5的晶态结构,有效阻止活性晶粒生长。V=O与V-O-V键在P作用下向催化剂内层移动,并被高度扭曲,催化剂表面生成磷酸盐物质,晶格氧数量明显减少,钒平均氧化态下降,催化剂供氧能力减弱。活性测试表明,催化剂P/V越高,它对苯甲腈选择性也越好,其中V3+离子和O2-空位扮演了重要的角色。认为VPO催化剂中内层V=O氧化-还原中心与P-OH的B酸中心共同形成了一个复合活性中心,P/V比在1到2之间的VPO/硅胶催化剂都具有较好催化性能。在440℃时甲苯转化率达到97%,对苯甲腈的选择性达到94%,故在此温度时苯甲腈产率约为91.2%。

VPO and VPO/Silica-gel catalysts with a variety of phosphorus content were prepared and characterized by XRD, FTIR and TPR. Ammoxidation of toluene to benzonitrile was also investigated on those prepared VPO/silica-gel catalysts. It was found that V2O5 crystal is destroyed sharply with P-adding ,V=O and V-O-V bond are distorted and moves to the inside of VPO catalysts, on the surface of catalysts produce some phosphates; The quantity of the lattice oxygen and average oxidation number of vanadium ions decrease, however the activity of the lattice oxygen is enhanced. Correlation of the phase composition and catalytic activity indicated that VPO/silica-gel with P/V=1~2 has better catalytic performance, and the more phosphates content, the higher selectivity in ammoixdation of toluene, which V3+ make a important role. It was proposed that the oxidation-reduction center V=O on internal layer of catalysts and the acidic site center P-OH compose a complex activity center. The maximal activity and selectivity in ammoxidation arrive at 97% and 94% respectively at 440℃, and the yield of benzonitrile can be 91.2%.