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首页> 外文期刊>Catalysis Today >Comparison of structural and catalytic properties of monometallic Mo and V oxides and M1 phase mixed oxides for oxidative dehydrogenation
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Comparison of structural and catalytic properties of monometallic Mo and V oxides and M1 phase mixed oxides for oxidative dehydrogenation

机译：单金属MO和V氧化物结构和催化性能的比较和M1相混合氧化物氧化脱氢

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Mo and V containing oxides are among the most important oxidative dehydrogenation catalysts. The effects of differences in structure and compostion among SiO2 supported VOx, unsupported V2O5 and MoO3 and M1 phase MoV mixed oxide catalysts on catalytic properties are probed using their reactivity and dehydrogenation selectivity in oxidative conversion of ethane (C2H6) and cyclohexane (C6H12). The C2H6 and C6H12 activation rates are nearly insensitive to VOx loading on SiO2 at low loadings that predominantly form monovanadate species, but decrease at high loadings due to the formation of V2O5 nanoparticles with low V dispersion. The C?H activation enthalpies are lower at high loadings and in unsupported V2O5, suggesting that intrinsic reactivity of V2O5 nanoparticles is higher than monovanadates. The C2H6/C6H12 rate ratios are below 0.01 on all VOx/SiO2 catalysts, consistent with weaker C?H bonds in C6H12, but are higher on V2O5 nanoparticles than on low loading VOx/SiO2 samples. MoO3 samples exhibit lower rates and higher activation energies than VOx/SiO2 and V2O5 samples, and similar C2H6/C6H12 rate ratios as V2O5. M1 phase MoVTeNb and MoV mixed oxides contain onedimensional micropores of size similar to C2H6 but much smaller than C6H12; preparation methods significantly affect their elemental composition, accessible micropore volumes and surface areas. Post-synthesis treatment of MoVTeNbO with H2O2 improves M1 phase purity, and increases in C2H6 and C6H12 activation rates are consistent with increase in their intrapore and external surface areas. The C2H6 and C6H12 activation rates in MoVO without Te and Nb are higher than values predicted from MoVTeNbO and their surface micropores and external surface areas, because higher V content in MoVO increases their reactivity by slightly decreasing activation energies. The C2H6/C6H12 rate ratios in these samples are much higher than VOx/SiO2, V2O5, and MoO3 and roughly correlate with internal/external surface ratios, which is consistent with C2H6 and C6H12 activation occurring inside and outside the pores, respectively. The M1 phase samples exhibit much higher selectivity than VOx/SiO2, V2O5, and MoO3, but among the M1 phase samples the selectivity is slightly lower in MoVO than in MoVTeNbO. Local structure and composition affect reactivity in M1 phase oxides and oxides without heptagonal micropores, but C2H6/C6H12 rate ratios and C2H4 selectivities are much higher in the M1 phase, which confirms for a broad range of oxides previously proposed roles of micropores in activating C2H6 selectively.
机译：含钼和钒的氧化物是最重要的氧化脱氢催化剂之一。利用SiO2负载VOx、无负载V2O5、MoO3和M1相MoV混合氧化物催化剂在乙烷（C2H6）和环己烷（C6H12）氧化转化中的反应活性和脱氢选择性，探讨了它们的结构和组成差异对催化性能的影响。C2H6和C6H12的活化率在低负载下对SiO2上的VOx负载几乎不敏感，主要形成单钒酸盐物种，但在高负载下由于形成具有低V分散的V2O5纳米颗粒而降低。C？H活化焓在高负载和无载体的V2O5中较低，表明V2O5纳米颗粒的固有反应性高于单钒酸盐。在所有VOx/SiO2催化剂上，C2H6/C6H12速率比均低于0.01，与较弱的C？C6H12中的H键，但V2O5纳米颗粒上的H键高于低负载VOx/SiO2样品上的H键。与VOx/SiO2和V2O5样品相比，MoO3样品的速率更低，活化能更高，C2H6/C6H12速率比与V2O5相似。M1相MoVTeNb和MoV混合氧化物含有尺寸类似于C2H6但远小于C6H12的一维微孔；制备方法显著影响其元素组成、可获得的微孔体积和表面积。用H2O2对MoVTeNbO进行合成后处理可提高M1相纯度，C2H6和C6H12活化率的增加与其孔内和外表面积的增加一致。不含Te和Nb的MoVO中C2H6和C6H12的活化率高于MoVTeNbO及其表面微孔和外表面面积的预测值，因为MoVO中较高的V含量通过略微降低活化能增加其反应性。这些样品中的C2H6/C6H12速率比远高于VOx/SiO2、V2O5和MoO3，并大致与内/外表面比相关，这与孔内和孔外分别发生的C2H6和C6H12活化一致。M1相样品的选择性比VOx/SiO2、V2O5和MoO3高得多，但在M1相样品中，MoVO的选择性略低于MoVTeNbO。局部结构和组成会影响M1相氧化物和无七边形微孔氧化物的反应性，但M1相的C2H6/C6H12速率比和C2H4选择性要高得多，这证实了之前提出的微孔在选择性激活C2H6中的广泛氧化物作用。

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