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首页> 外文期刊>Catalysis science & technology >Ammoxidation of 2-methylpyrazine to 2-cyanopyrazine over Nb-V oxides: marked effect of the Nb/V ratio on the catalytic performance
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Ammoxidation of 2-methylpyrazine to 2-cyanopyrazine over Nb-V oxides: marked effect of the Nb/V ratio on the catalytic performance

机译：NB-V氧化物上2-甲基吡嗪与2-丙型吡嗪的氧化剂：NB/V比对催化性能的明显影响

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摘要

A series of bulk Nb-V-containing mixed oxide catalysts with varying Nb/V ratios were synthesized and studied by various solid-state characterization methods. Their catalytic performance was evaluated for the gas phase ammoxidation of 2-methylpyrazine (MP) to 2-cyanopyrazine (CP) that has received growing interest in the chemical industry, recently. The catalysts were characterised by BET-SA, XRD, UV-vis DRS, FTIR, XPS, and TEM. The BET surface area decreased continuously with increase in vanadia content. XRD data confirmed the changes in the crystalline phases with altering Nb/V ratios. UV-vis DRS and FTIR spectroscopic results showed the formation of various kinds of V-oxide species in the catalysts with change in V content. An increase in the concentration of vanadium changes the nature of VO_x species from isolated vanadia species to polymeric vanadia species and then to crystalline vanadia species. Among all the catalysts, the Nb-V-O catalyst with a Nb/V ratio of 1 exhibited the best performance in the ammoxidation reaction (i.e. X-MP -100% and selectivity to 2-CP ～70%). Additionally, a very high space-time yield of CP (>440 g_(CP) kg_(cat)~(-1) h~(-1)) could be successfully achieved. This best catalyst sample revealed two-dimensional polymeric V-oxide species. TEM and SEM showed the formation of a rod-shaped nanoparticle morphology. XPS data revealed that the vanadium is present in two oxidation states (V~(5+) and V~(4+)) in the fresh catalyst (Nb/V = 1) and only one oxidation state (V~(5+)) in the spent catalyst.
机译：通过各种固态表征方法合成并研究了一系列具有不同NB/V比的含有不同NB/V比的混合氧化物催化剂。最近，评估了2-甲基吡嗪（MP）到2-氰基吡嗪（CP）的气相促催化性能，最近对化学工业产生了越来越兴趣。催化剂的特征是BET-SA，XRD，UV-VIS DRS，FTIR，XPS和TEM。 BET表面积随着Vanadia含量的增加而连续下降。 XRD数据证实了随着NB/V比的改变，结晶相的变化。 UV-VIS DR和FTIR光谱结果表明，在V含量变化的催化剂中形成了各种V-氧化物物种。钒的浓度的增加改变了VO_X物种的性质，从孤立的瓦纳迪亚物种到聚合物瓦纳迪亚物种，然后再到晶体化的Vanadia物种。在所有催化剂中，NB-V-O催化剂的NB/V比为1的催化剂在Ammoxidation反应中表现出最佳性能（即X-MP -100％，选择性为2-CP ～70％）。此外，可以成功实现CP（> 440 g_（cp）kg_（cat）〜（-1）H〜（-1））的非常高的时空产量。该最佳催化剂样品显示二维聚合物V-氧化物物种。 TEM和SEM显示了杆状纳米颗粒形态的形成。 XPS数据显示，钒存在于新鲜催化剂（NB/V = 1）中的两个氧化状态（V〜（5+）和V〜（4+））中，仅一个氧化态（V〜（5+）） ）在消费的催化剂中。

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