Abstract:

Vanadium phosphorus oxide (VPO) catalysts doped with different transition metals were prepared by impregnation method, and their catalytic performance for cyclohexane oxidation by NO₂ to adipic acid were tested. The XRD, XPS, H₂-TPR and UV-Vis DRS were used to investigate the effect of transition metal doping on the valence structure of vanadium in VPO catalysts and the catalytic performance for oxidation of cyclohexane. The results showed that the introduction of transition metals could change the phase structure ratio of β-VOPO₄ and (VO)₂P₂O₇ in VPO samples, thus changing the ratio of V⁵⁺ and V⁴⁺. In addition, the valence structure of vanadium in VPO catalysts played an important effect in the oxidation of cyclohexane to adipic acid by NO₂. The catalytic performance of M/AlVPO catalyst containing both V⁵⁺ and V⁴⁺ was significantly higher than that of the pure V⁵⁺ β-VOPO₄ and pure V⁴⁺ (VO)₂P₂O₇ catalysts. Among them, when Cu/AlVPO with V⁴⁺/V⁵⁺ of 0.52 was used as the catalyst, the conversion rate of cyclohexane was 65.4%, and the selectivity of adipic acid was 84.8% when Ni/AlVPO with V⁴⁺/V⁵⁺ of 0.66 was used as the catalyst.

Key words: VPO composite oxides, cyclohexane, adipic acid, catalytic oxidation, catalytic mechanism

摘要：

采用浸渍法制备不同钒价态结构的钒磷氧（VPO）复合氧化物催化剂，测试其对NO₂氧化环己烷制备己二酸的催化性能，并采用XRD、XPS、H₂-TPR和UV-Vis DRS等手段进行表征，考察不同过渡金属掺杂对VPO中钒价态结构的影响，以及催化氧化环己烷性能的影响。研究结果表明，过渡金属的引入能够改变VPO中β-VOPO₄和（VO）₂P₂O₇两种晶相结构，从而调变V⁵⁺ 和V⁴⁺ 的比例，且钒的价态比例对NO₂氧化环己烷反应具有重要影响。同时含有V⁵⁺ 和V⁴⁺ 的M/AlVPO催化剂的催化性能明显高于纯V⁵⁺ 的β-VOPO₄和纯V⁴⁺ 的（VO）₂P₂O₇催化剂。其中，以V⁴⁺/V⁵⁺ 为0.52的Cu/AlVPO为催化剂时环己烷的转化率最高为65.4%，以V⁴⁺/V⁵⁺ 为0.66的Ni/AlVPO为催化剂时己二酸的选择性最高为84.8%。

关键词: 钒磷氧复合氧化物, 环己烷, 己二酸, 催化氧化, 催化机理