Understanding effects of Ni particle size on steam methane reforming activity by combined experimental and theoretical analysis

Abstract

Fundamental understanding of the size dependent activity is essential to harness powers of the nanocatalysts.Here we report an experimental and theoretical study of the Ni particle size effect on activity of steam methane reforming (SMR) to achieve a better understanding of the size dependence of kinetic behavior at an atomic level. A kinetic study illustrated the higher forward methane turnover frequency on the smaller sized Ni particles. The size dependent activity was well reproduced by microkinetic modeling on a truncated octahedron model with the kinetic parameters estimated by the improved unity bond index-quadratic exponential potential (UBI-QEP) and the Brønsted-Evans-Polanyi (BEP) relationship. Microkinetic modeling suggested that the size-dependent activity of Ni catalysts is associated with surface-dependent activity. Much higher activity of Ni(211) than Ni(111) and Ni(100) accompanied by decreased Ni(211) surface fraction results in reduced Ni activity as particle size increasing. The activity of Ni( 111) is limited by high free energy barrier, while that of Ni( 100) is limited by surface C* and CH* blockage. This work offers a feasible approach to gain insight into size-dependent activity and to aid rational catalyst design that preparing extremely small Ni particles (≤ 6 nm) might be a good strategy for SMR.

Revealing the Effect of Nickel Particle Size on Carbon Formation Type in the Methane Decomposition Reaction

“…Another important factor to consider is that the CDM reaction has been proven to be structurally sensitive to nickel particle size; small nickel particles showed high methane cracking activity [69]. That can be explained by the lower activation barriers of CH x species dissociation on uncoordinated crystallographic planes (e.g., Ni (553) or Ni (100)) compared with the packed surface (e.g., Ni (111)), which are greater on small-sized particles [70]. On the contrary, a large amount of Ni (111) surfaces are present on the large nickel particles.…”

Methane decomposition into CO x ‐free hydrogen over a Ni‐based catalyst: An overview

“…CMD reaction is also structurally sensitive to Ni particle size where small Ni particles show high methane decomposition activity 146 . This can be explained by the lower activation barriers of methyl species dissociation on uncoordinated crystallographic planes such as Ni (553) or Ni (100) compared with the packed surface Ni (111), which are greater on small‐sized particles 146,147 . Different from small Ni particles, a large amount of Ni (111) surfaces exists on the large Ni particles.…”

A Review on Particle Size Effect in Metal‐Catalyzed Heterogeneous Reactions

“…Besides above, Ni catalysts were also widely used in methane reforming reactions, which is a main process for hydrogen production in current chemical insustry. [ 205‐209 ] It has been demonstrated that the catalytic performance tightly relies on Ni particle size. For example, Chen and co‐workers reported that small Ni particles exhibited a higher activity than large ones in the size range of 2 to 16 nm in steam methane reforming (SMR) over Ni catalyst.…”

“…For example, Chen and co‐workers reported that small Ni particles exhibited a higher activity than large ones in the size range of 2 to 16 nm in steam methane reforming (SMR) over Ni catalyst. [ 206 ] By combining experimental and theoretical analysis, they claimed that Ni(211) is the most active surface, compared with Ni(111) and Ni(100). Thus, the size‐dependent activity was attributed to the decrease of the fraction of Ni LCSs as Ni particle size increases, consistent with the work by Nørskov et al .…”