Kinetic insights into the effect of promoters on Co/Al2O3 for Fischer-Tropsch Synthesis
Kinetic insights into the effect of promoters on Co/Al2O3 for Fischer-Tropsch Synthesis
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DOI：
10.1016/j.cej.2022.136655
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发表时间：
2022-04
影响因子：
15.1
通讯作者：
Xiaoli Yang;Jia Yang;Tao Zhao;W. Qian;Yalan Wang;A. Holmen;Wei Jiang;Der-Nien Chen;Haoxi Ben-Hao
中科院分区：
文献类型：
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作者：
Xiaoli Yang;Jia Yang;Tao Zhao;W. Qian;Yalan Wang;A. Holmen;Wei Jiang;Der-Nien Chen;Haoxi Ben-Hao
采用Rh、Ir、Sb和Ga作为Co/Al2O3的促进剂，系统地研究了Co基催化剂Fischer - Tropsch合成中促进剂效应的基本原理。各种表征表明，Rh-和Ir-促进催化剂具有较高的分散性和还原性，从而提高了吸附性能，而Sb-和Ga-促进催化剂则表现出相反的结果，因为合金的形成抑制了Co的可及性。根据实验结果和动力学计算，提出了这些催化剂的活化能与活化熵的线性关系。此外，稳态同位素瞬态动力学分析（SSITKA）表明，促进剂主要通过影响表面chx浓度来改变CO反应速率，而链生长速率常数会影响产物分布。由于CoRhA和CoIrA极大地提高了chx浓度，抑制了链的生长能力，因此它们具有较高的CO反应速率和ch4选择性。而coba和CoGaA抑制了chx浓度和内在活性，但增强了链生长能力，从而显示出较低的CO反应速率和ch4选择性。反应性和选择性的差异是由于不同助剂对钴催化剂的活化焓改变了吸附强度。这些发现提供了对促进剂效应的动力学见解，并为优化催化剂铺平了道路。
The fundamentals of promoter effects in the Fischer − Tropsch synthesis over Co-based catalysts were systematically investigated by employing the Rh, Ir, Sb and Ga as promoters of Co/Al2O3. Various characterizations showed the higher dispersion and reducibility over Rh- and Ir- promoted catalysts would cause a promoted adsorption property, while the Sb- and Ga- promoted catalysts showed a contrary result because the formation of alloy suppressed the accessibility of Co species. Based on the experimental results and kinetic calculations, a linear relationship for the activation energies of these catalysts as a function of activation entropies was proposed. Besides, steady state isotopic transient kinetic analysis (SSITKA) revealed that promoters mainly affected the surface CHxconcentration to alter the CO reaction rate, and the chain growth rate constants would affect the product distribution. Since CoRhA and CoIrA greatly enhanced the CHxconcentration and inhibited the chain growth ability, they owned a higher CO reaction rate and CH4selectivity. While the CoSbA and CoGaA suppressed the CHxconcentration and intrinsic activity, but enhanced the chain growth ability, thereby revealing a lower CO reaction rate and CH4selectivity. Furthermore, the reactivity and selectivity difference were attributed to the modification of adsorption strength dictated by the enthalpy of activation on cobalt catalysts with different promoters. These findings provide kinetic insights into the promoter effects and pave the way for optimizing catalysts.