Department of Materials Science and Engineering, Lehigh University, 5 East Packer Avenue, Bethlehem, PA 18015-3195, USA.
Phys Chem Chem Phys. 2011 Oct 14;13(38):17395-404. doi: 10.1039/c1cp21136f. Epub 2011 Aug 31.
Several niobium phosphate phases have been prepared, fully characterized and tested as catalysts for the selective oxidation of ethane to ethylene. Three distinct niobium phosphate catalysts were prepared, and each was comprised predominantly of a different bulk phase, namely Nb(2)P(4)O(15), NbOPO(4) and Nb(1.91)P(2.82)O(12). All of the niobium phosphate catalysts showed high selectivity towards ethylene, but the best catalyst was Nb(1.91)P(2.82)O(12), which was produced from the reduction of niobium oxide phosphate (NbOPO(4)) by hydrogen. It was particularly selective for ethylene, giving ca. 95% selectivity at 5% conversion, decreasing to ca. 90% at 15% conversion, and only produced low levels of carbon oxides. It was also determined that the only primary product from ethane oxidation over this catalyst was ethylene. Catalyst activity also increased with time-on-line, and this behaviour was ascribed to an increase of the concentration of the Nb(1.91)P(2.82)O(12) phase, as partially transformed NbOPO(4), formed during preparation, was converted to Nb(1.91)P(2.82)O(12) during use. Catalysts with predominant phases of Nb(2)P(4)O(15) and NbOPO(4) also showed appreciable activity and selectivities to ethylene with values around 75% and 85% respectively at 5% ethane conversion. The presence of phosphorous is required to achieve high ethylene selectivity, as orthorhombic and monoclinic Nb(2)O(5) catalysts showed similar activity, but displayed selectivities to ethylene that were <20% under the same reaction conditions. To the best of our knowledge, this is the first time that niobium phosphates have been shown to be highly selective catalysts for the oxidation of ethane to ethylene, and demonstrates that they are worthy candidates for further study.
已经制备了几种磷酸铌相，并对其进行了充分的表征和测试，以作为乙烷选择性氧化为乙烯的催化剂。制备了三种不同的磷酸铌催化剂，它们主要由不同的体相组成，分别为 Nb(2)P(4)O(15)、NbOPO(4)和 Nb(1.91)P(2.82)O(12)。所有磷酸铌催化剂对乙烯都表现出高选择性，但最好的催化剂是 Nb(1.91)P(2.82)O(12)，它是由氢气还原氧化铌磷酸 (NbOPO(4))制备而成的。它对乙烯的选择性特别高，在 5%转化率下的选择性约为 95%，在 15%转化率下降低至约 90%，并且只产生少量的碳氧化物。还确定了在这种催化剂上进行的乙烷氧化的唯一主要产物是乙烯。催化剂活性也随在线时间的增加而增加，这种行为归因于 Nb(1.91)P(2.82)O(12)相浓度的增加，因为在制备过程中形成的部分转化的 NbOPO(4)在使用过程中转化为 Nb(1.91)P(2.82)O(12)。主要相为 Nb(2)P(4)O(15)和 NbOPO(4)的催化剂也表现出相当高的乙烷转化为乙烯的活性和选择性，在 5%乙烷转化率下分别约为 75%和 85%。高乙烯选择性需要磷的存在，因为正交和单斜 Nb(2)O(5)催化剂具有相似的活性，但在相同反应条件下，对乙烯的选择性小于 20%。据我们所知，这是首次证明磷酸铌是乙烷氧化为乙烯的高选择性催化剂，并且表明它们是进一步研究的有价值的候选物。
