As the commercial catalyst in the propane direct dehydrogenation (PDH) reaction, one of the biggest challenges of Pt catalysts is coke formation, which severely reduces activity and stability. In this work, a first-principles DFT-based kinetic Monte Carlo simulation (kMC) is performed to understand the origin of coke formation, and an effective method is proposed to curb coke. The conventional DFT calculations give a complete description of the reaction pathway of dehydrogenation to propylene, deep dehydrogenation, and C–C bond cracking. The rate-limiting step is identified as the dissociative adsorption of propane. Moreover, a comparison between different exchange-correlation functionals indicates the importance of van der Waals corrections for the adsorption of propane and propylene. The lateral interactions between the surface adsorbates are significant, which implies that mean field microkinetic modeling might not adequately describe the reaction process. There are two distinct stages in PDH, which are quick deactivation and steady state, respectively, as revealed from the kMC simulation. The precursor of coke mainly formed during the quick deactivation. The calculations indicate that the geometries of the active sites for the dehydrogenation and deep reactions are different. Therefore, the availability of surface sites is a crucial factor in the formation of propylene and side products. The active sites from quick deactivation are mainly occupied by C₂/C₁ species, which are hard to remove. On the other hand, the surface sites that are left are mainly active toward dehydrogenation to propylene due to the geometry constraint. Therefore, a stable activity and selectivity is reached. Furthermore, the effect of hydrogen molecules in the input stream is also explored. The calculations indicate that the inclusion of hydrogen in PDH reactants not only enhances the forward reactions to the propylene formation but also reduces the consumption of the resulted propylene during the reaction. Therefore, hydrogen is very helpful to the selectivity increase in PDH in addition to other effects. Overall, the current study lays out a solid base for the future optimization of the Pt catalysts in PDH and we propose that the fine control of the surface sites on Pt has paramount importance in reducing coke formation.

中文翻译：

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从kMC模拟中揭示铂催化剂上丙烷直接脱氢中焦炭前体的贾纳斯特性。

作为丙烷直接脱氢（PDH）反应中的商用催化剂，Pt催化剂的最大挑战之一是结焦，这严重降低了活性和稳定性。在这项工作中，基于第一原理的基于DFT的动力学蒙特卡洛模拟（kMC）旨在了解焦炭形成的起源，并提出了一种有效的抑制焦炭的方法。传统的DFT计算给出了脱氢生成丙烯，深度脱氢和CC键断裂的反应路径的完整描述。限速步骤被确定为丙烷的解离吸附。此外，不同交换相关功能之间的比较表明范德华校正对于丙烷和丙烯吸附的重要性。表面被吸附物之间的横向相互作用是显着的，这意味着平均场微动力学模型可能不足以描述反应过程。从kMC仿真中可以看出，PDH中有两个截然不同的阶段，分别是快速停用和稳定状态。焦炭的前体主要是在快速失活过程中形成的。计算表明，用于脱氢和深度反应的活性位的几何形状是不同的。因此，表面位点的可用性是形成丙烯和副产物的关键因素。快速停用的活动位点主要被C占据 从kMC仿真中可以看出，它们分别是快速停用和稳态。焦炭的前体主要是在快速失活过程中形成的。计算表明，用于脱氢和深度反应的活性位的几何形状是不同的。因此，表面位点的可用性是形成丙烯和副产物的关键因素。快速停用的活动位点主要被C占据 从kMC仿真中可以看出，它们分别是快速停用和稳态。焦炭的前体主要是在快速失活过程中形成的。计算表明，用于脱氢和深度反应的活性位的几何形状是不同的。因此，表面位点的可用性是形成丙烯和副产物的关键因素。快速停用的活动位点主要被C占据₂ / C ₁种，很难去除。另一方面，由于几何形状的限制，剩下的表面位点主要对脱氢成丙烯有活性。因此，达到了稳定的活性和选择性。此外，还研究了输入流中氢分子的作用。计算表明，在PDH反应物中包含氢不仅增强了向丙烯形成的正向反应，而且减少了反应期间所得丙烯的消耗。因此，除了其他作用外，氢对提高PDH的选择性非常有帮助。总体而言，当前的研究为将来在PDH中优化Pt催化剂奠定了坚实的基础，我们建议对Pt表面位点的精细控制对于减少焦炭形成至关重要。