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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 different P / V ratios were prepared by impregnation method. The catalysts were characterized by XRD, FTIR and TPR. Their catalytic performances were investigated in the reaction of toluene ammoxidation with benzonitrile. It was found that the introduction of P destroys the crystalline structure of V2O5 and effectively prevents the growth of active grains. V = O and V-O-V bonds move toward the catalyst inner layer under the action of P and are highly distorted. Phosphate materials are formed on the surface of the catalyst, the quantity of lattice oxygen is obviously decreased, the average oxidation state of vanadium is decreased, and the oxygen supply capability of the catalyst is weakened. The activity test showed that the higher the P / V of the catalyst, the better its selectivity to benzonitrile. The V3 + ions and O2-vacancies play an important role. It is considered that the VPO / silica catalyst of VPO / silica gel with VP / silica catalyst has the same catalytic activity as the V-O oxidation-reduction center of VPO catalyst and the B acid center of P-OH. . At 440 ℃, the conversion of toluene reaches 97% and the selectivity to benzonitrile reaches 94%. Therefore, the yield of benzonitrile at this temperature is about 91.2%.