There is an ongoing debate about the structure sensitivity of nickel-based catalysts during CO2 methanation. No consensus has yet been reached whether this reaction is nickel particle size-dependent and if so, what would be the optimal size. Metal oxide supports that are typically used for this type of studies, could greatly affect the catalytic activity during CO2 methanation. We use an inert graphitic carbon support (C), resulting in relatively little interaction with the nickel particles. This allows us to study intrinsic particle size effects of Ni for CO2 activation and methanation. A series of Ni/C catalysts with Ni particle sizes in the range of 3.5-10 nm was successfully designed via deposition of nickel onto high specific surface area (~500 m2/g) graphitic sheets. We used simple incipient wetness impregnation with an aqueous nickel nitrate solution. By carefully varying the Ni weight-loading (5-15 %) and heat treatment procedures (300 – 400 °C) different particle sizes were obtained. Figure 1a and c reveal highly dispersed Ni particles on the carbon support. The catalysts are remarkably stable during CO2 hydrogenation for 125h at 330 °C and 30 barg. This is noteworthy, since graphitic carbon has relatively weak interaction with the nanoparticles and sintering is one of the main deactivation mechanisms. The CH4 selectivity during this reaction is highly conversion-dependent and is close to 100% at high conversions. A 3 to 4-fold increase in activity (TOF) was observed with increasing particle sizes from 4 to 13 nm after catalysis. This indicates that intrinsically, there is an effect of particle size. Up to 13 nm, larger nickel particles contain more active surface sites for CO2 hydrogenation than smaller ones. Our results show that Ni/C model catalysts allow to uncouple particle size and support effects, which is important for fundamental studies, and can be tested under industrially relevant reaction conditions (high pressures and long-term testing).

Intrinsic particle size effects of nickel particulate catalysts for CO2 methanation

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.