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Ni–Mo sulfide nanosized catalysts from water-soluble precursors for hydrogenation of aromatics under water gas shift conditions
Pure and Applied Chemistry ( IF 1.8 ) Pub Date : 2020-06-25 , DOI: 10.1515/pac-2019-1115
Anna Vutolkina 1 , Aleksandr Glotov 1, 2 , Ilnur Baygildin 1 , Argam Akopyan 1 , Marta Talanova 1 , Maria Terenina 1 , Anton Maximov 1, 3 , Eduard Karakhanov 1
Affiliation  

Abstract The unsupported catalysts were obtained during hydrogenation by in situ high-temperature decomposition (above 300 °C) of water-soluble metal precursors (ammonium molybdate and nickel nitrate) in water-in-oil (W/O) emulsions stabilized by surfactant (SPAN-80) using elemental sulfur as sulfiding agent. These self-assembly Ni–Mo sulfide nanosized catalysts were tested in hydrogenation of aromatics under CO pressure in water-containing media for hydrogen generation through a water gas shift reaction (WGSR). The composition of the catalysts was determined by XRF and active sulfide phase was revealed by XRD, TEM and XPS techniques. The calculations based on TEM and XPS data showed that the catalysts are highly dispersed. The surfactant was found to affect both dispersion and metal distribution for Ni and Mo species, providing shorter slab length in terms of sulfide particle formation and stacking within high content of NiMoS phase. Catalytic evaluation in hydrogenation of aromatics was performed in a high-pressure batch reactor at T = 380–420 °С, p(CO) = 5 MPa with water content of 20 wt.% and CO/H2O molar ratio of 1.8 for 4–8 h. As shown experimentally with unsupported Ni–Mo sulfide catalysts, the activity of aromatic rings depends on the substituent therein and decreases as follows: anthracene>>1-methylnaphthalene≈2-methylnaphthalene>1,8-dimethylnaphthale-ne>>1,3-di-methylnaphthalene>2,6-dimethylnaphthalene≈2,3-dimethylnaphthalene>2-ethyl-naphthalene. The anthracene conversion reaches up to 97–100% for 4 h over the whole temperature range, while for 1MN and 2MN it doesn’t exceed 92 and 86% respectively even at 420 °С for 8 h. Among dimethyl-substituted aromatics the higher conversion of 45% was achieved for 1,8-dimethylnaphthalene with 100% selectivity to tetralines at 400 °С for 6 h. Similar to 1- and 2-methylnaphtalenes, the hydrogenation of asymmetric dimethyl-substituted substrate carries out through the unsubstituted aromatic ring indicating that steric factors influence on the sorption mechanism over active metal sites. The catalysts were found to be reused for at least six cycles when the hydrogenation is sulfur-assisted preventing metal oxide formation. It was established, that at the first 2–3 h known as the induction period, the oxide catalyst precursors formed slowly by metal salt decomposition, which reveals that it is the rate-determining step. The sulfidation is rather fast based on high catalytic activity data on 2MN conversion retaining at 93–95% upon recycling.

中文翻译:

水煤气变换条件下用于芳烃加氢的水溶性前驱体的镍钼硫化物纳米催化剂

摘要 在加氢过程中,通过表面活性剂稳定的油包水(W/O)乳液中水溶性金属前体(钼酸铵和硝酸镍)的原位高温分解(高于 300 °C)获得无载体催化剂。 SPAN-80) 使用元素硫作为硫化剂。这些自组装 Ni-Mo 硫化物纳米催化剂在含水介质中在 CO 压力下通过水煤气变换反应 (WGSR) 制氢进行芳烃加氢测试。催化剂的组成由 XRF 测定,活性硫化物相由 XRD、TEM 和 XPS 技术揭示。基于 TEM 和 XPS 数据的计算表明催化剂高度分散。发现表面活性剂会影响 Ni 和 Mo 物种的分散和金属分布,就硫化物颗粒的形成和在高含量 NiMoS 相中的堆积而言,提供更短的板坯长度。芳烃加氢的催化评价在高压间歇式反应器中进行,T = 380–420 °С,p(CO) = 5 MPa,含水量为 20 wt.%,CO/H2O 摩尔比为 1.8,用于 4– 8 小时。无负载的 Ni-Mo 硫化物催化剂实验表明,芳环的活性取决于其中的取代基并按如下方式降低:蒽>>1-甲基萘≈2-甲基萘>1,8-二甲基萘>>1,3-二甲基萘>2,6-二甲基萘≈2,3-二甲基萘>2-乙基-萘。在整个温度范围内,4 小时内蒽转化率高达 97-100%,而对于 1MN 和 2MN,即使在 420°С 下 8 小时,其转化率也分别不超过 92% 和 86%。在二甲基取代的芳烃中,1,8-二甲基萘的转化率高达 45%,在 400°С 6 小时内对四氢化萘的选择性为 100%。与 1- 和 2- 甲基萘相似,不对称二甲基取代底物的氢化通过未取代的芳环进行,表明空间因素影响活性金属位点的吸附机制。当氢化是硫辅助防止金属氧化物形成时,发现催化剂可重复使用至少六个循环。已经确定,在被称为诱导期的前 2-3 小时,氧化物催化剂前体通过金属盐分解缓慢形成,这表明这是决定速率的步骤。
更新日期:2020-06-25
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