Ni/MCF催化剂的改性及其催化甲烷二氧化碳重整反应性能研究

Modification of Ni/MCF catalyst and its catalytic performance for dry reforming of methane

  • 摘要: 本工作针对甲烷二氧化碳重整反应中Ni基催化剂的烧结和积炭问题,利用2-甲基咪唑与Ni2+形成金属-有机框架结构(MOFs),以MOFs为前驱体,在氮化改性的介孔泡沫硅(MCF)载体上构建了金属-载体相互作用较强的Ni基催化剂。XRD、TEM、BET、H2-TPR、XPS、TG等表征结果表明,通过高温程序氮化法对MCF载体进行N掺杂改性能够提高活性金属的分散度、降低粒径、增强金属-载体相互作用力、降低催化剂还原度、增强金属-载体电子相互作用力、增加催化剂表面高价态Niδ+的含量。通过2-甲基咪唑与Ni2+络合的方式改性催化剂前驱体为三维的金属-有机框架结构,经高温空气煅烧后,在催化剂表面形成了嵌入的块状结构的硅酸镍物种,硅酸镍物种中的活性金属主要以高价态Niδ+的形式存在,高分散于催化剂表面表现出了强的金属-载体相互作用力。N掺杂改性MCF载体与2-甲基咪唑改性催化剂前驱体两种改性叠加对催化剂性能的提高更为显著。700 ℃时,Ni/N-MCF-MI催化剂表现出优异的DRM催化性能,其CH4和CO2的转化率分别为 78%和 83%,且反应10 h性能稳定,具有良好的抗积炭和抗烧结能力。

     

    Abstract: Dry Reforming of Methane (DRM) to efficiently produce synthesis gas (H2/CO), an important chemical raw material. Ni-based catalyst has been widely studied due to its abundant reserves, low price and certain catalytic performance, and is a common DRM reaction catalyst with industrialization prospects. However, under the reaction conditions of high temperature (>700 ℃) and carbon-containing sources (CH4 and CO2), Ni-based catalysts tend to be deactivated due to sintering and carbon deposition. At present, the sintering and carbon deposition problems of Ni-based catalysts have not been solved. In this work, aiming at the sintering and carbon deposition of Ni-based catalyst in the dry reforming of methane reaction, firstly, mesoporous foam-based silicon MCF support with high specific surface area and abundant pores was synthesized and supported with nickel catalyst. The MCF support was modified by temperature program nitridation with alkaline additives to synthesize N-MCF support and supported with nickel catalyst. Ni dispersion is good on N-MCF and MCF. Ni-based catalysts with strong metal-support interaction were constructed on nitrogenous modified mesoporous silicon foams (MCF) with MOFs as precursor using 2-methylimidazole and Ni2+ to form MOFs. XRD, TEM, SEM, BET, H2-TPR, XPS, TG and other characterization results show that The N doping modification of MCF support by high temperature program nitriding method can improve the dispersion of active metal, reduce the particle size, enhance the metal- support interaction force, reduce the catalyst reduction degree, enhance the metal- support electron interaction force, and increase the content of high price state Niδ+ on the catalyst surface. The catalyst precursor was modified into a three-dimensional metal-organic framework structure by complexing 2-methylimidazole with Ni2+. After calcination by high temperature air, an embedded massive nickel silicate species was formed on the catalyst surface. The active metals in nickel silicate species mainly exist in the form of high price Niδ+ and are highly dispersed on the catalyst surface, showing strong metal- support interaction force, which makes the active metals of the catalyst have good dispersion and small particle size. When the stability test is conducted at 700 ℃, the Ni/MCF-MI catalyst shows excellent DRM catalytic performance. The conversion rates of CH4 and CO2 were 72% and 73% respectively, and the reaction performance was stable for 10 h. The Ni/N-MCF-MI catalyst with N doping modified MCF support and 2-methylimidazole modified catalyst precursor showed the best DRM catalytic performance. Under the stability test at 700 ℃, the conversion rates of CH4 and CO2 were 78% and 83%, respectively, and the reaction performance was stable for 10 h. After the reaction, the weight loss of Ni/N-MCF-MI catalyst is 16%, the weight loss rate is the lowest, and there is no obvious sintering, agglomeration and growth of active metal nanoparticles. N doping modified MCF support and 2-methylimidazole modified catalyst precursor can both improve the dispersion of active metal, reduce particle size, and enhance the metal- support interaction force. The catalyst modified with both N additive and 2-methylimidazole has the best DRM catalytic performance and certain advantages of inhibiting the growth of carbon nanotubes and the agglomeration and sintering of Ni particles.

     

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