The conversion of CO2 into carbon feedstock via CO2 hydrogenation to methane requires a stable catalyst for reaction at high temperatures. Zeolite NaY (abbreviated hereafter as NaY) synthesized from naturally occurring kaolin provides a stable support for Ni nanoparticles. Kaolin can be further dealuminated using sulfuric acid to reduce the Si/Al ratio, but the presence of the remaining sulfur is detrimental to the formation of NaY. The objective of the present study was to synthesize NaY from dealuminated metakaolin, using a method that minimizes the detrimental effects of sulfur, and to investigate the effect of its activity on CO2 methanation. Kaolin from Bangka Belitung, Indonesia, was calcined at 720°C for 4 h to form metakaolin (M) and subsequently treated with sulfuric acid to form dealuminated metakaolin (DM). Excess sulfur was removed by washing with deionized water at 80°C. Zeolite NaY was then synthesized from the M and DM via a hydrothermal method; the relationship between morphology, structural properties, and the catalytic activity of NaY was determined for CO2 methanation at 200–500°C. The presence of excess sulfur following dealumination of metakaolin produced NaY with small surface area and porosity. After Ni impregnation, the synthesized NaY exhibited significant catalytic activity and stability for the reaction at 250–500°C. Analysis by scanning electron microscopy and high-resolution transmission electron microscopy showed the formation of well-defined octahedral structures and large surface areas of ~500 m2/g when NaY was synthesized using DM. Catalytic activity indicated significant conversion of CO2 (67%) and CH4 selectivity (94%) of Ni/NaY from DM in contrast to only 47% of CO2 conversion with 77% of CH4 selectivity for Ni/NaY synthesized from M. Dealuminated metakaolin also produced robust NaY, which indicated no deactivation at 500°C. The combination of well-defined crystallite structures, large surface area, and small Al contents in NaY synthesized from DM helped in CO2 conversion and CH4 selectivity for the reaction at 200–500°C.

中文翻译：

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脱铝偏高岭土合成沸石 NaY 作为 Ni 支持 CO2 加氢制甲烷

通过 CO2 加氢生成甲烷将 CO2 转化为碳原料需要稳定的催化剂才能在高温下进行反应。由天然存在的高岭土合成的沸石 NaY（以下简称 NaY）为 Ni 纳米颗粒提供了稳定的支撑。高岭土可以使用硫酸进一步脱铝以降低 Si/Al 比，但剩余硫的存在不利于 NaY 的形成。本研究的目的是从脱铝偏高岭土合成 NaY，使用一种最大限度地减少硫的有害影响的方法，并研究其活性对 CO2 甲烷化的影响。来自印度尼西亚 Bangka Belitung 的高岭土在 720°C 下煅烧 4 小时以形成偏高岭土 (M)，随后用硫酸处理以形成脱铝偏高岭土 (DM)。通过在 80°C 下用去离子水洗涤去除多余的硫。然后通过水热法从 M 和 DM 合成沸石 NaY；在 200-500°C 下，对 CO2 甲烷化，确定了 NaY 的形态、结构特性和催化活性之间的关系。偏高岭土脱铝后过量硫的存在产生具有小表面积和孔隙率的NaY。Ni浸渍后，合成的NaY在250-500°C下对反应表现出显着的催化活性和稳定性。扫描电子显微镜和高分辨率透射电子显微镜的分析表明，当使用 DM 合成 NaY 时，形成了明确的八面体结构和~500 m2/g 的大表面积。催化活性表明，来自 DM 的 Ni/NaY 的 CO2 转化率显着（67%）和 CH4 选择性（94%），而从 M 合成的 Ni/NaY 的 CO2 转化率仅为 47%，CH4 选择性为 77%。脱铝偏高岭土也产生了稳定的 NaY，表明在 500°C 下没有失活。由 DM 合成的 NaY 中明确的微晶结构、大的表面积和小的 Al 含量的组合有助于在 200-500°C 下反应的 CO2 转化和 CH4 选择性。