Synthesis of transition metal oxides with nanopores and their catalytic properties for alkane isomerization

研究了h_2 -还原MoO_3与贵金属催化戊烷和丙烷-2-醇转化的性能。Pt、Pd、Rh和Ir/MoO_3催化剂在773 K条件下还原12 h后，其戊烷异构化活性和丙烷-2-醇脱水活性无明显差异，h2还原的Ru/MoO_3催化剂的异构化和脱水活性低于其他催化剂。随着Ru负荷量的增加，h2 -还原Ru/MoO_3的异构化和脱水活性提高，而h2 -还原Pt/MoO_3的异构化和脱水活性变化不大。XRD和TPR研究表明，Ru/MoO_3的还原过程随Ru的加入量而变化。与此相反，Pt/MoO_3的还原与氢钼青铜H_xMoO_3的生成无关。从这些结果可以看出，H_xMoO_3的还原可以产生戊烷异构化和丙烷-2-醇脱水的活性相。为了阐明H_xMoO_3的作用，研究了H_2还原对氢钼青铜（H_<1.55>MoO_3）物理性能和催化性能的影响。H_2还原增大了H_<1.55>MoO_3和Pt/MoO_3的表面积，但没有增大MoO_3的表面积。H_<1.55>MoO_3成为戊烷异构化和丙烷-2-醇脱水的活性催化剂。h_2还原的H_<1.55>MoO_3的催化活性与h_2还原的Pt/MoO_3相当，且远高于h_2还原的MoO_3。在H_<1.55>MoO_3和Pt/MoO_3还原过程中，氢钼青铜相分解后生成氧化钼（MoO_xH_y）。相比之下，MoO_3被还原为MoO_2而没有形成氢青铜。结果表明，氢钼青铜的H_2还原反应生成的MoO_xH_y相可以作为戊烷和丙烷-2-醇转化的活性相。

The catalytic properties of H_2-reduced MoO_3 with noble metal for the conversions of pentane and propan-2-ol were studied. No appreciable difference appeared in the pentane isomerization activity and in the propan-2-ol dehydration activity among Pt, Pd, Rh, and Ir/MoO_3 catalysts after reduction at 773 K for 12 h. H_2-reduced Ru/MoO_3 exhibited the lower isomerization and dehydration activities than other catalysts. The isomerization and the dehydration activities of H2-reduced Ru/MoO_3 was improved by an increase in the amount of Ru loading, while those of H_2-reduced Pt/MoO_3 changed very little. XRD and TPR studies showed that the reduction process of Ru/MoO_3 varied with the amount of Ru. By contrast, reduction of Pt/MoO_3 involved the formation of hydrogen molybdenum bronze, H_xMoO_3, irrespective of the amount of Pt. We suggest from these results that reduction of H_xMoO_3 can yield the active phase for pentane isomerization and for propan-2-ol dehydration. In order to manifest the roles of H_xMoO_3, the effects of H_2 reduction on the physical and catalytic properties of one type of hydrogen molybdenum bronze, H_<1.55>MoO_3, were studied. H_2 reduction enlarged the surface areas of H_<1.55>MoO_3 and Pt/MoO_3, but not the surface area of MoO_3. H_<1.55>MoO_3 became an active catalyst for pentane isomerization and for propan-2-ol dehydration after H_2 reduction. The catalytic activities of H_2-reduced H_<1.55>MoO_3 were comparable to those of H_2-reduced Pt/MoO_3, and were much higher than those of H_2-reduced MoO_3. In reduction of H_<1.55>MoO_3 and Pt/MoO_3, molybdenum oxyhydride, MoO_xH_y, was formed after the decomposition of the hydrogen molybdenum bronze phase. By contrast, MoO_3 was reduced to MoO_2 without the formation of hydrogen bronze. We propose from these results that H_2 reduction of hydrogen molybdenum bronze will generate the MoO_xH_y phase that can act as the active phase for the conversions of pentane and propan-2-ol.