Plasma-assisted Ni catalysts: Toward highly-efficient dry reforming of methane at low temperature

Abstract

Dry reforming of methane (DRM) reaction can convert primary greenhouse gases (CH4 and CO2) to value-added chemicals (H2 and CO), but generally suffers from harsh reaction conditions (>700 °C) and inevitable deactivation of catalysts. In this work, we report supported Ni catalysts based on a topotactic transformation process from the layered double hydroxides (NiZnAl−LDHs) precursors. Structural characterizations (XRD, HRTEM, CO chemisorption) verify a uniform distribution of Ni nanoparticles (∼7 nm) on the mixed metal oxides support with a high dispersion (denoted as Ni/MMO). With the assistance of non-thermal plasma (NTP), the optimal sample (Ni/MMO−S2) exhibits a good catalytic conversion of CH4 (∼69%) and CO2 (∼54%) at low temperatures (30–60 °C), which is comparable with the activity of thermocatalytic process at ∼650 °C without NTP. The energy efficiency of NTP-assisted catalysis process is an order of magnitude higher than that of thermocatalytic process at ∼650 °C and enhances by 80% relative to NTP-alone process at low temperatures. The Ni/MMO−S2 catalyst shows satisfactory stability after 600 min stability test, with a slight decrease in conversion (within ∼1%). In addition, a combined study including catalytic evaluations, operando OES, XAFS and XPS verifies that metallic Ni species acts as active center, which can promote the dissociation of CH4 and CO2 into highly reactive intermediate species with the assistance of NTP. This synergistic effect between plasma and Ni catalyst remarkably decreases the apparent activation energy by ∼50%, accounting for the high catalytic performance at low temperatures. This work demonstrates a promising synergistic catalysis strategy between plasma and catalysts at low temperatures, which can be extended to other reactions operated under harsh conditions.