Dry Reforming of Methane on Single-Site Ni/MgO Catalysts: Importance of Site Confinement

Abstract

Single-site catalysts (SSCs) have drawn considerable attention, because of their superior behaviors in catalysis. However, the origin of promoting the effect of a single site is not well understood. Here, we take the single-atom Ni1/Mg­(100) and single-site Ni4/Mg­(100) catalysts as a case study to elucidate their behaviors under the complex dry reforming of methane (DRM, CO2 + CH4→ 2CO + 2H2) reaction by combining theoretical modeling (density functional theory and kinetic Monte Carlo simulation) and experimental studies. The synergy between single Ni atom and MgO is found to improve the binding property of MgO; yet, it is not enough to dissociate CO2 and CH4. It can be achieved by the single-site Ni4/MgO­(100) catalyst, enabling the formations of CO, H2, and H2O under the DRM conditions. During this process, coking, as observed for bulklike Ni particles, is eliminated. By confining the reaction to occur at the isolated Ni sites in the SSC, the Ni4/MgO­(100) catalyst is able to balance the CO2 and CH4 activations, which is identified as the key for tuning the DRM activity and selectivity of Ni/MgO catalysts. The theory-identified promotion introduced by increasing the size of MgO-supported Ni clusters from Ni1 to Ni4 and the MgO-introduced site confinement of single-site catalysts are verified by corresponding experimental studies, highlighting the essential roles of confined sites in tuning the performance of SSCs during complex catalytic processes.

Atomically dispersed nickel as coke-resistant active sites for methane dry reforming

“…In light of the thermodynamic stability of CH 3 to subsequent C–H cleavage over our catalysts, the appearance of CO as a major product in our catalytic system appears paradoxical. However, a recent report of DRM over Ni 4 clusters (which also show good carbon deposition resistance 52 ) identified the oxidation of CH 3 to CH 3 O as an alternative route to CO following initial methane activation, as also proposed for Ni 1 –Ru 1 /CeO 2 42 . We therefore considered this alternative route for transforming reactively formed CH 3 to CO without carbon deposition (Fig.…”

Recent Progresses in the Design and Fabrication of Highly Efficient Ni-Based Catalysts With Advanced Catalytic Activity and Enhanced Anti-coke Performance Toward CO2 Reforming of Methane

“…Besides, its strong Lewis basicity catalyst has a strong chemisorption effect toward CO 2 and can inhibit coke deposition by accelerating the coke-eliminating reaction (Zhang et al, 2018). Zuo et al (2018) used theoretical modeling and experimentation to study the catalytic performance of singlesite Ni/MgO catalysts in CRM reactions. As the particle size of Ni increases, the single-site Ni/MgO catalyst provided stronger bindings and more sufficient sites to activate CH 4 and CO 2 .…”

CH<sub>4</sub>-CO<sub>2</sub> reforming: challenges and outlook

“…"超干重整"过程则是提高原料中CO 2 的含量至CO 2 / CH 4 =3远离热力学积碳区, 过量的CO 2 则用Fe还原为 CO, 但该过程是化学计量反应, 单位质量Fe的CO 2 转 化量很低 [184] . 微波反应器 [185] 、等离子体反应器 [186] 、 光反应器 [187] 、膜反应器 [188~190] 以及太阳能反应器 [191] 等也被用于DRM反应的研究, 但都存在处理量小或难 的性质, 甚至不具 备DRM活性 [146,180] . 而要使单原子Ni表现更多的金属 性, 其与载体的相互作用则不宜太强, 因此在高温下 很容易团聚烧结.…”