Investigating the dynamic changes in the dispersion of a catalyst with time-on-stream (TOS), in-situ, provides insights into the mechanism of catalyst deactivation. Coating catalysts by Atomic Layer Deposition (ALD) has been previously shown to provide resistance against coking and sintering in various reaction systems. In this study, a commercial 20 wt. % Ni on alumina catalyst is conformally coated with 5, 10, and 20 cycles of ALD alumina and tested for the Dry Reforming of Methane (DRM) reaction, and an in-situ sequential H2-CO pulse chemisorption technique is used to monitor the changes in metallic Ni dispersion for the uncoated and overcoated catalysts. Dynamic changes in dispersion with TOS show that the rate of decrease in the dispersion is much faster for the uncoated catalyst than for the 5-cycle ALD-coated catalyst. Although the 5-ALD catalyst has lower initial dispersion, the dispersion is relatively stable for ~40 h DRM TOS at 650 °C, 1 atm. The rate of decrease in dispersion is ~0.11%h-1 for the uncoated catalyst versus ~0.025%h-1 for the 5-ALD catalyst. TEM images of the reduced and used catalysts show that the average crystallite size for the uncoated commercial catalyst increases from 8.5 nm to 24.5 nm during 40 h DRM TOS, indicating severe sintering. Under similar conditions, the 5-ALD catalyst retains the initial crystallite size, and the post-reaction crystallite size is ~8.7 nm. Lower carbon formation rate was observed on the 5-ALD catalyst which can be attributed to the smaller particle size of the Ni crystallites in the ALD-coated catalyst. The pattern of CO adsorption and simultaneous H2 desorption is found to be different in the 5-ALD catalyst versus the uncoated catalyst, which appears to be due to the effect of ALD overcoat on H2 and CO chemisorption. The discussion of the pulse trends of CO and H2 on polycrystalline Ni, particularly the peculiar CO retention effect on the ALD coated systems could benefit the design of highly selective industrial catalysts.

In situ estimation of Ni dispersion via sequential H2-CO pulse chemisorption: Case study of an ALD-coated catalyst

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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