VPO催化剂制备条件对其催化甲苯氨氧化反应性能的影响

Effect of Preparation Conditions on Catalytic Performance of VPO Catalyst for Toluene Ammoxidation

用浸渍法制备了负载型钒磷氧 (VPO)催化剂 ,并以甲苯氨氧化合成苯甲腈为探针反应 ,考察了载体、还原剂、P/V比和V2 O5负载量对催化剂性能的影响 .结果表明 ,大比表面积SiO2 负载的VPO催化剂性能稳定 ,在高温下也具有较好的选择性 .采用不同还原剂制备的催化剂在反应一段时间后活性趋于一致 ,表明催化剂活性中心是在反应气氛下形成的 .P/V比对催化剂活性和结构影响较大 ,P的加入破坏了V2 O5的晶型结构 ,使磷酸盐物种从催化剂体相向表面聚集 ,减少了催化剂表面存在的过度氧化物种O-和O-2 的数量 ,选择性氧化物种晶格氧 (O2 -)起主要氧化作用 ,提高了催化剂的选择性 .V2 O5负载量增大 ,催化剂活性提高 ,但生成苯甲腈的选择性降低 .表面单分子层覆盖的VOx 可能是反应的活性位和选择性位 .

Supported VPO catalyst was prepared by impregnation method, and the effect of preparation conditions such as support, reductant, P/V molar ratio and V2O5 loading on the catalytic performance of VPO for toluene ammoxidation was investigated. VPO supported on SiO2 with large surface area showed stable catalytic performance even at high temperature. After a period of reaction, the activity of catalysts prepared by using different reductants became similar, indicating that the active centers were formed under reaction atmosphere. P/V molar ratio had a great influence on the structure and performance of the catalyst. The crystal structure of V2O5 was destroyed sharply, and P-O-P together with V-O-P species segregated on the catalyst surface with the addition of P, the active adsorbed oxygen species O- and O-2(-) for deep oxidation were removed, which resulted in the increase of the selectivity for benzonitrile but decrease of the catalytic activity. The activity of VPO was improved while the selectivity for benzonitrile decreased with the increase of V2O5 loading. It could be proposed that the monolayer VOx species on catalyst surface were the active and selective sites for toluene ammoxidation.