Comparison of structural and catalytic properties of monometallic Mo and V oxides and M1 phase mixed oxides for oxidative dehydrogenation
Comparison of structural and catalytic properties of monometallic Mo and V oxides and M1 phase mixed oxides for oxidative dehydrogenation
复制标题
DOI：
10.1016/j.cattod.2020.04.046
复制
发表时间：
2020-04
期刊：
影响因子：
5.3
通讯作者：
Leelavathi Annamalai;Sopuruchukwu Ezenwa;Yanliu Dang;H. Tan;S. Suib;P. Deshlahra
中科院分区：
文献类型：
--
作者：
Leelavathi Annamalai;Sopuruchukwu Ezenwa;Yanliu Dang;H. Tan;S. Suib;P. Deshlahra
含Mo和V的氧化物是最重要的氧化脱氢催化剂之一。考察了SiO2负载的VOx、非负载的V2 O 5和MoO 3以及M1相MoV复合氧化物催化剂在乙烷（C2 H6）和环己烷（C6 H12）氧化转化反应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。C2 H6和C6 H12的活化速率几乎不敏感VOx负载在SiO2上在低负载量，主要形成单钒酸盐物种，但降低在高负载量，由于形成V2 O 5纳米粒子与低V分散。在高负载量和未负载的V2 O 5中，C-H活化能较低，表明V2 O 5纳米颗粒的固有反应性高于单钒酸盐。所有VOx/SiO2催化剂上的C2 H6/C6 H12速率比均低于0.01，与C6 H12中较弱的C-H键一致，但V2 O 5纳米颗粒上的C2 H6/C6 H12速率比高于低负载量VOx/SiO2样品。MoO 3样品比VOx/SiO2和V2 O 5样品具有更低的反应速率和更高的反应活化能，而C2 H6/C6 H12的反应速率比与V2 O 5相似。M1相MoVTeNb和MoV混合氧化物含有尺寸类似于C2 H6但比C6 H12小得多的一维微孔;制备方法显著影响其元素组成、可接近的体积和表面积。MoVTeNbO与H2 O2的合成后处理提高了M1相的纯度，并且C2 H6和C6 H12活化速率的增加与其孔内和外表面积的增加一致。MoVO中不含Te和Nb的C2 H6和C6 H12活化速率高于从MoVTeNbO及其表面微孔和外表面积预测的值，因为MoVO中较高的V含量通过略微降低活化能来增加其反应性。这些样品中的C2 H6/C6 H12速率比远高于VOx/SiO2、V2 O 5和MoO 3，并且大致与内/外表面比相关，这与分别在孔内部和外部发生的C2 H6和C6 H12活化一致。M1相样品表现出比VOx/SiO2、V2 O 5和MoO 3高得多的选择性，但在M1相样品中，MoVO的选择性略低于MoVTeNbO。局部结构和组成影响M1相氧化物和没有七边形微孔的氧化物的反应性，但C2 H6/C6 H12速率比和C2 H4选择性在M1相中要高得多，这证实了先前提出的微孔在活化C2 H6选择性中的作用。
Mo and V containing oxides are among the most important oxidative dehydrogenation catalysts. The effects of differences in structure and compostion among SiO2supported VOx, unsupported V2O5and MoO3and 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 C2H6and C6H12activation rates are nearly insensitive to VOxloading on SiO2at low loadings that predominantly form monovanadate species, but decrease at high loadings due to the formation of V2O5nanoparticles with low V dispersion. The C–H activation enthalpies are lower at high loadings and in unsupported V2O5, suggesting that intrinsic reactivity of V2O5nanoparticles is higher than monovanadates. The C2H6/C6H12rate ratios are below 0.01 on all VOx/SiO2catalysts, consistent with weaker C–H bonds in C6H12, but are higher on V2O5nanoparticles than on low loading VOx/SiO2samples. MoO3samples exhibit lower rates and higher activation energies than VOx/SiO2and V2O5samples, and similar C2H6/C6H12rate ratios as V2O5. M1 phase MoVTeNb and MoV mixed oxides contain one-dimensional micropores of size similar to C2H6but much smaller than C6H12; preparation methods significantly affect their elemental composition, accessible micropore volumes and surface areas. Post-synthesis treatment of MoVTeNbO with H2O2improves M1 phase purity, and increases in C2H6and C6H12activation rates are consistent with increase in their intrapore and external surface areas. The C2H6and C6H12activation 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/C6H12rate ratios in these samples are much higher than VOx/SiO2, V2O5, and MoO3and roughly correlate with internal/external surface ratios, which is consistent with C2H6and C6H12activation 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/C6H12rate ratios and C2H4selectivities are much higher in the M1 phase, which confirms for a broad range of oxides previously proposed roles of micropores in activating C2H6selectively.