Cooperativity and Dynamics Increase the Performance of NiFe Dry Reforming Catalysts

Abstract

The dry reforming of methane (DRM), i.e., the reaction of methane and CO to form a synthesis gas, converts two major greenhouse gases into a useful chemical feedstock. In this work, we probe the effect and role of Fe in bimetallic NiFe dry reforming catalysts. To this end, monometallic Ni, Fe, and bimetallic Ni-Fe catalysts supported on a MgAlO matrix derived via a hydrotalcite-like precursor were synthesized. Importantly, the textural features of the catalysts, i.e., the specific surface area (172-178 m/g), pore volume (0.51-0.66 cm/g), and particle size (5.4-5.8 nm) were kept constant. Bimetallic, NiFe with Ni/(Ni + Fe) = 0.8, showed the highest activity and stability, whereas rapid deactivation and a low catalytic activity were observed for monometallic Ni and Fe catalysts, respectively. XRD, Raman, TPO, and TEM analysis confirmed that the deactivation of monometallic Ni catalysts was in large due to the formation of graphitic carbon. The promoting effect of Fe in bimetallic Ni-Fe was elucidated by combining operando XRD and XAS analyses and energy-dispersive X-ray spectroscopy complemented with density functional theory calculations. Under dry reforming conditions, Fe is oxidized partially to FeO leading to a partial dealloying and formation of a Ni-richer NiFe alloy. Fe migrates leading to the formation of FeO preferentially at the surface. Experiments in an inert helium atmosphere confirm that FeO reacts via a redox mechanism with carbon deposits forming CO, whereby the reduced Fe restores the original Ni-Fe alloy. Owing to the high activity of the material and the absence of any XRD signature of FeO, it is very likely that FeO is formed as small domains of a few atom layer thickness covering a fraction of the surface of the Ni-rich particles, ensuring a close proximity of the carbon removal (FeO) and methane activation (Ni) sites.

Advances in catalytic conversion of methane and carbon dioxide to highly valuable products

“…As reported by Damyanova et al., Ni/MgAl 2 O 4 catalyst showed much better performance for DRM than Ni/Al 2 O 3 . Furthermore, NiFe/ Mg x Al y O z catalyst is even better than Ni/Mg x Al y O z (Figure ) . The promoting effect of Fe was attributed to its dynamic redox reaction under dry reforming conditions, ensuring a close proximity of the carbon removal (FeO) and methane activation (Ni) sites.…”

“…Rate of methane consumption at 650°C over catalysts: (■) Ni‐ MA , (▲) Ni4Fe1‐ MA , (●) Ni3Fe1‐ MA , (□) Ni1Fe1‐ MA , (△) Ni1Fe3‐ MA and (○) Fe‐ MA ( MA : Mg x Al y O z ). Reprinted with permission from []. Copyright (2017) American Chemical Society.…”

“…Furthermore, NiFe/ Mg x Al y O z catalyst is even better than Ni/ Mg x Al y O z (Figure 3). 155 The promoting effect of Fe was attributed to its dynamic redox reaction under dry reforming conditions, ensuring a close proximity of the carbon removal (FeO) and methane activation (Ni) sites. In addition, rare earth elements (Sc, Y, Ce, and Pr) exhibited promoting effect on Ni/ Mg x Al y O z catalysts, leading to the improved catalytic stability and coke resistance due to the enhanced surface basicity, abundant oxygen vacancies, superior redox properties, and highly dispersed Ni particles.…”

Nanoalloy Materials for Chemical Catalysis

“…f) The rate of methane consumption as a function of time in the methane dry reforming reaction and catalysis schematic view. Reproduced with permission . Copyright 2017, American Chemical Society.…”

Recent Advances in Supported Metal Catalysts for Syngas Production from Methane

“…For instance, catalysts reduced at 650 • C as opposed to 850 • C has shown a decrease in coke formation by up to 50%, as was measured by the TPO experiments. In order to further understand the synergism in Ni-Fe bimetallic systems and in order to understand the mechanism through which the Ni-Fe alloys function, the reader is advised to refer to the work by Kim et al [61]. The bimetallic catalyst with small crystallite size was prepared using to improve the catalyst activity and stability.…”