Carbon Nanofiber Growth Rates on NiCu Catalysts: Quantitative Coupling of Macroscopic and Nanoscale In Situ Studies

Since recently, gas-cell transmission electron microscopyallowsfor direct, nanoscale imaging of catalysts during reaction. However,often systems are too perturbed by the imaging conditions to be relevantfor real-life catalyzed conversions. We followed carbon nanofibergrowth from NiCu-catalyzed methane decomposition under working conditions(550 & DEG;C, 1 bar of 5% H-2, 45% CH4, and 50%Ar), directly comparing the time-resolved overall carbon growth ratesin a reactor (measured gravimetrically) and nanometer-scale carbongrowth observations (by electron microscopy). Good quantitative agreementin time-dependent growth rates allowed for validation of the electronmicroscopy measurements and detailed insight into the contributionof individual catalyst nanoparticles in these inherently heterogeneouscatalysts to the overall carbon growth. The smallest particles didnot contribute significantly to carbon growth, while larger particles(8-16 nm) exhibited high carbon growth rates but deactivatedquickly. Even larger particles grew carbon slowly without significantdeactivation. This methodology paves the way to understanding macroscopicrates of catalyzed reactions based on nanoscale in situ observations.

Automated summary

Gas-cell transmission electron microscopy has enabled direct, nanoscale imaging of catalysts during reaction. We compared the growth rates of carbon nanofibers measured gravimetrically in a reactor and observed through electron microscopy, and found good agreement. This allowed for detailed insight into the contribution of individual catalyst nanoparticles in these heterogeneous catalysts to overall carbon growth. The methodology of nanoscale in situ observations paves the way for understanding macroscopic rates of catalyzed reactions.