Nanoparticle Growth in Supported Nickel Catalysts during Methanation Reaction—Larger is Better

Abstract

A major cause of supported metal catalyst deactivation is particle growth by Ostwald ripening. Nickel catalysts, used in the methanation reaction, may suffer greatly from this through the formation of [Ni(CO)4 ]. By analyzing catalysts with various particle sizes and spatial distributions, the interparticle distance was found to have little effect on the stability, because formation and decomposition of nickel carbonyl rather than diffusion was rate limiting. Small particles (3-4 nm) were found to grow very large (20-200 nm), involving local destruction of the support, which was detrimental to the catalyst stability. However, medium sized particles (8 nm) remained confined by the pores of the support displaying enhanced stability, and an activity 3 times higher than initially small particles after 150 h. Physical modeling suggests that the higher [Ni(CO)4 ] supersaturation in catalysts with smaller particles enabled them to overcome the mechanical resistance of the support. Understanding the interplay of particle size and support properties related to the stability of nanoparticles offers the prospect of novel strategies to develop more stable nanostructured materials, also for applications beyond catalysis.

Effect of ZrO2 on catalyst structure and catalytic methanation performance over Ni-based catalyst in slurry-bed reactor

“…Compared to the spent catalyst Ni/Al-IP, the spent catalyst Ni/ 20ZA-IP showed less carbon deposition, indicating that the addition of a certain amount of ZrO 2 improved the anti-carbon deposition. Ni/Zr-IP catalyst showed no significant carbon deposition, but some Ni aggregations were observed on the catalyst surface, which was probably due to that CO adsorbed on the Ni surface and formed Ni(CO) 4 at low temperature, leading to Ni aggregation through Ostwald ripening [43,44]. However, further studies are needed, because Ni/Al-IP catalyst showed no obvious Ni aggregations under the same reaction conditions.…”

Recent Advances on the Design of Group VIII Base-Metal Catalysts with Encapsulated Structures

“…Munnik et al drew the relationship between Ni NPs growth via the Oswald ripening and Ni particle sizes by using a mesoporous silica support. 94 Ni…”

Influence of calcination temperature on textural and structural properties, reducibility, and catalytic behavior of mesoporous γ-alumina-supported Ni–Mg oxides by one-pot template-free route

“…For the NiO-MgO/c-MA samples calcined at higher temperatures (P500°C), the reduction of Ni 2+ ions might be the rate-determining step and Ni atoms were released very slowly for the growth of Ni crystallites because of the stronger interaction with the support. In this case, Ostwald ripening, namely monoatomic species or small clusters diffuse from small to larger particles [23], might be the dominant mechanism for Ni crystallite growth rather than migration and coalescence of Ni nanoparticles. In a word, the Ni atoms or small Ni clusters with high-surface energies could overcome the attachment on the support to move toward the small Ni crystallites initially formed in the framework and produce larger crystallites, breaking the pore wall.…”

“…Numerous investigations have been directed toward the characteristics and distribution of surface nickel compounds on the support, the reducibility of nickel oxide species, the shape and size of metallic nickel particles, the catalyst composition, and the interplay of metal particles and the support properties, which strongly influence the catalytic activity, stability, and resistance to carbon deposition [21][22][23][24][25][26][27]. Although most of the obtained results are very interesting, the correlation among the active metal species, the catalyst structures, and the catalytic properties in the reforming reactions is still ambiguous, even though it is pivotal to understand and to abate its irreversible deactivation, due to the inherently inhomogeneous metal particle dispersion and porous structure in the catalysts obtained by the impregnation method.…”