添加剂对共沉淀法制备的VPO催化剂的影响

研究了添加剂对用于选择性氧化正丁烷为顺丁烯二酸酐的VPO催化剂的结构和性能的影响.催化剂采用共沉淀法制备,添加元素为Zr,Co,Ce,Zn,Sn,K,Ba和Bi等.催化剂性能测试在固定床微反应器内于常压下进行.结果表明,添加剂对催化剂性能有很大的影响.各种组分对正丁烷氧化的促活顺序为VPO-Zr＞VPO-Co＞VPO-Zn＞VPO-Sn＞VPO-Bi＞VPO-Ce＞VPO-Ba＞VPO-K＞VPO,而对正丁烷氧化为顺丁烯的选择性促活顺序为VPO-Zr＞VPO-Ce＞VPO-Zn＞VPO-Sn＞VPO-Co＞VPO-Bi＞VPO＞VPO-Ba＞VPO-K.XRD, FTIR和TGA/DTG测试结果表明,添加剂的加入并未使活化前后催化剂的本体结构发生明显改变.所有VPO催化剂前体均主要含VOPO4·0.5H2O,而活化后的催化剂主要含有(VO)2P2O7和少量α-VOPO4.XPS测试证实催化剂表面有P,V和O等元素富集的现象,而且表面氧物种数与催化剂活性直接相关.

Influence of Additives on Various VPO Catalysts Prepared by Coprecipitation Process

The effect of additives on the structures and properties of various VPO catalysts used for the selective oxidation of n-butane to maleic anhydride was investigated. A series of VPO catalysts were prepared by coprecipitation process with the addition of Zr, Co, Ce, Zn, Sn, K, Ba and Bi as promoters. The catalytic performance test was conducted in a fixed-bed micro-reactor at atmospheric pressure. The results show that the catalytic behavior is affected remarkably by additives. For n-butane oxidation activity, the effect of various elements follows the order of VPO-Zr＞VPO-Co＞VPO-Zn＞VPO-Sn＞VPO-Bi＞VPO-Ce＞VPO-Ba＞VPO-K＞VPO. For MA (Maleic Anhydride) selectivity, the promoting effect is in the order of VPO-Zr＞VPO-Ce＞VPO-Zn＞VPO-Sn＞VPO-Co＞VPO-Bi＞VPO＞VPO-Ba＞VPO-K. Test results of catalysts including XRD, FTIR and TGA/DTG indicate that no remarkable change occurs in the bulk structure due to the addition of elements, both for precursor and final catalysts. All precursor catalysts are composed of VOPO4*0.5H2O, while in the final samples, (VO)2P2O7 is formed accompanied by less amounts of α-VOPO4. XPS measurement suggests the enrichment of P, V and O on the surface of catalysts, and the amount of surface oxygen species is directly related to the catalyst activity.