CO2 甲烷化反应被认为是解决 CO2 利用难题的重要手段之一,其中 NiO/MgO 催化剂具有广阔的应用前景,如何提高NiO/MgO催化剂的比表面积成为其实际应用的关键.本文通过沉积-沉淀法在高比表面积的SiO2载体上负载NiO/MgO催化剂,制备出了NiO/MgO/SiO2 催化剂.研究了MgO含量、催化剂煅烧温度和还原温度对催化剂结构和甲烷化性能的影响.采用 X 射线衍射、程序升温还原、N2 吸附-脱附等温线、程序升温脱附、X 射线光电子能谱和场发射透射电子显微镜等技术手段对催化剂进行了表征.结果表明,合适的 MgO 含量既能够对 SiO2 形成较好的阻隔以避免 NiO 与 SiO2 的反应,又可与 NiO 形成对甲烷化有利的 Ni1-xMgxO 固溶体.适当的煅烧温度能够在形成 Ni1-xMgxO 固溶体的同时避免对反应不利的 NiMgSiO4 的形成.此外,通过调控还原温度还能够调变 Ni0 和Ni1-xMgxO 的比例,从而使二者在催化体系中起到协同作用,促进 CO2 甲烷化反应.30%MgO 含量、550℃煅烧、550℃还原后的 Ni30MgSi-550-550R 催化剂在 CO2 甲烷化反应催化剂性能测试中表现出最佳的催化活性,且在 350℃、30000 mL/(g·h)空速的测试条件下展现出 200 h 的稳定性,这是由于在催化剂表面具有适当的 Ni0/Ni1-xMgxO比例和对应的充足的H2 和CO2 活化位点.在高比表面积的SiO2 上负载NiO/MgO催化剂、在SiO2 表面进行固相反应和通过还原温度调控Ni0-Ni1-xMgxO活性对的策略为用于CO2甲烷化反应的催化剂设计提供了一种新思路.
NiO/MgO Catalysts Loaded onto a SiO2 Surface for CO2 Methanation
CO2 methanation is a potential approach for CO2 utilization.The NiO/MgO catalyst is a promising catalyst for this reaction,but achieving an adequate specific surface area remains a challenge.Herein,NiO/MgO/SiO2 cata-lysts were prepared by loading NiO/MgO catalysts on the support of SiO2 with a high specific surface area according to the deposition-precipitation method.The effects of MgO content,calcination temperature,and reduction tempera-ture on the structure and methanation performance were systematically investigated.The catalysts were characterized using X-ray diffraction,temperature-programmed reduction,N2 adsorption-desorption isotherms,temperature-programmed desorption,X-ray photoelectron spectroscopy,and transmission electron microscopy.The results showed that the appropriate MgO content could not only inhibit the reaction between NiO and SiO2,but also form a solid solution of Ni1-xMgxO.In the catalyst calcined at a suitable temperature,the solid solution of Ni1-xMgxO was formed while avoiding the formation of NiMgSiO4,which is unfavorable for CO2 methanation.Furthermore,the relative contents of Ni0 and Ni1-xMgxO could be tailored via the reduction temperature.The catalyst showed a suitable Ni0-Ni1-xMgxO ratio,which allowed it to play a synergistic role in the catalytic system for CO2 methanation.The Ni30MgSi-550-550R catalyst,which was calcined at 550℃,reduced at 550℃,and set at 30%MgO content,exhibited the best catalytic activity for CO2 methanation and maintained stable operation for 200 h during a stability test under the conditions of 350℃and 30000 mL/(g·h)via the moderate surface Ni0/Ni1-xMgxO ratio and a suffi-cient number of activation sites for H2 and CO2.The strategy for loading NiO/MgO catalysts on SiO2 with a high spe-cific surface area,solid-phase reaction on SiO2,and modulation of Ni0-Ni1-xMgxO activation pairs via the reduction temperature provides a new approach for CO2 methanation.
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