On the reactivity of carbon formed from CO CVD over Ni(1 1 1)/TiO2

Structural effect of Ni/TiO2 on CO methanation: improved activity and enhanced stability

CO methanation over a supported Ni catalyst has attracted increasing attention for its applications in synthetic natural gas production, CO removal for ammonia synthesis and fuel cells, among others. However, the deactivation of the Ni catalyst caused by sintering and carbon deposition hinders further application of the Ni catalyst. The activity of Ni catalysts needs further improvement as well. In this work, the structural effect of the Ni/TiO₂ catalyst on CO methanation was investigated. A plasma decomposition, initiated at room temperature and operated around 150 °C, of the nickel precursor was applied to prepare the catalyst. Compared to the thermally decomposed Ni/TiO₂ catalyst, the plasma-decomposed catalyst shows improved activity with enhanced stability. The catalyst characterization shows that the plasma-decomposed Ni/TiO₂ catalyst possesses smaller Ni particle size and higher Ni dispersion, resulting in improved coke resistance and enhanced anti-sintering ability for CO methanation. The present study confirms that a catalyst with good activity for CO methanation possesses good activity for CO₂ methanation as well, if the CO₂ methanation takes the CO methanation pathway.

Highly dispersed Ni/TiO₂ catalyst with Ni (111) obtained by cold plasma decomposition shows improved activity and carbon resistance for CO methanation.

Nanowire-Based Materials as Coke-Resistant Catalyst Supports for Dry Methane Reforming

In this paper, nanowire-supported catalysts loaded with nickel are shown to be coke resistant compared to nanoparticle-supported catalysts. Specifically, Ni-loaded titania-based nanowire catalysts were tested with the dry methane reforming process in a laboratory-scale continuous packed-bed atmospheric reactor. The CO2 conversion rate stayed above 90% for over 30 h on stream under coke-promoting conditions, such as high flow rates, low temperatures, and a high ratio of CH4 to CO2. The coke (CxHy, x>>y) on the spent catalyst surface for both nanowire- and nanoparticle-supported catalysts was characterized by TGA, temperature-programmed reduction (TPR), and electron microscopy (SEM/TEM/EDS), and it was revealed that the types of carbon species present and their distribution over the morphology-enhanced materials played a major role in the deactivation. The CO2 conversion activity of Ni supported on titania nanoparticles was reduced from ~80% to less than 72% in 30 h due to the formation of a graphitic coke formation. On the other hand, Ni particles supported on nanowires exhibited cube-octahedral morphologies, with a high density of non- (111) surface sites responsible for the increased activity and reduced graphitic coke deposition, giving a sustained and stable catalytic activity during a long time-on-stream experiment.