Synthesis of Ni/Mo/N catalyst and its application in benzene hydrogenation in the presence of thiophene

Abstract

Ni/Mo/N catalysts made to have an interstitial structure gave high catalytic activity and sulfur tolerance in the hydrotreating of coal liquid fuel to produce high performance jet fuel. The dissolving of N atoms into the metal lattices to make the interstitial structure is difficult to control, and the preparation conditions of the precursor synthesis and the crystallinity of the precursors were changed to monitor how N atoms were inserted into the metal lattice. Ni/Mo/N catalysts were prepared by a one pot synthesis using ammonium molybdate [(NH 4 ) 6 Mo 7 O 24 ·4H 2 O] and nickel acetate [Ni(CH 3 COO) 2 ·4H 2 O] and the decomposition of hexamine under an argon atmosphere at 650 °C. Benzene hydrogenation was used as a model reaction to evaluate catalytic activity. Benzene was hydrogenated over the Ni/Mo/N catalyst at 250 °C and 3 MPa in a fixed bed reactor in the absence and presence of thiophene to also test the Ni/Mo/N catalysts for sulfur tolerance. X-ray diffraction analysis showed that the formation of different precursors and use of different aging times affected the composition of the Ni/Mo/N catalysts, and also determined the crystal phases in the Ni/Mo/N catalysts. Ni 2 Mo 3 N, Mo 2 C, and Ni metal phases were present in the most active Ni/Mo/N catalyst which gave a conversion of benzene of 93% and selectivity to cyclohexane of almost 100%. The atomic ratio of Ni/Mo in the most active Ni/Mo/N catalyst was 5/4 as determined by energy dispersive X-ray spectroscopy. Benzene hydrogenation over the Ni/Mo/N catalyst in the presence of thiophene led to a decline in benzene conversion from 72% to 50% due to the formation of MoS 2 . Ni/Mo/N间隙型催化剂具有高的加氢活性及良好耐硫性, 可应用于煤液化油加氢精制高性能喷气燃料. N原子由于只占据晶格间隙位置, 在进入Ni/Mo过程中会因不占据晶格中的特定晶位, 容易从金属晶格溢出导致无法形成稳定的Ni/Mo/N间隙型催化剂. 为此, 本文利用前驱体晶型控制的方式来实现Ni/Mo/N催化剂合成. 采用络合物分解一步法, 考察了不同结晶过程和老化时间对合成的Ni/Mo/N催化剂用于苯加氢反应活性影响, 并采用X射线衍射、X射线光电子能谱和透射电镜-能量色散X射线光谱对催化剂结构组成进行表征. XRD分析结果显示, 钼酸铵[(NH 4 ) 6 Mo 7 O 24 ∙4H 2 O]、乙酸镍[Ni(CH 3 COO) 2 ∙4H 2 O]和六亚甲基四胺(HMT)添加顺序、结晶过程和老化时间直接影响催化剂组成, 并决定Ni/Mo/N晶相的形成. 结晶过程慢速搅拌速度和短老化时间有利于合成含Ni 2 Mo 3 N, Mo 2 C和Ni晶相的高活性Ni/Mo/N间隙型催化剂, 使苯加氢制环己烷模型反应苯的最大转化率达93%, 环己烷选择性为100%. 含0.01 wt%噻吩的存在使苯转化率由72%降至50%, XPS分析结果表明, 催化剂表面形成的MoS 2 是催化剂活性降低的重要因素. An unsupported Ni/Mo/N interstitial catalyst with high catalytic performance and sulfur tolerance is prepared by the complex decomposition of HMT at 650 °C in one pot synthesis.