This study investigates changes in dispersion with time-on-stream of a Ni catalyst coated with alumina by Atomic Layer Deposition (ALD) in Dry Reforming of Methane (DRM) conditions. A 20 wt% commercial Ni catalyst is coated with 5, 10, and 20 ALD cycles and tested for DRM at 650 degrees C, 1 atm for 40 h. Using an in-situ H-2-CO pulse chemisorption technique, it is found that the rate of decline in catalyst dispersion is more rapid in the uncoated catalyst (similar to 0.11%h(-1)) than 5-ALD catalyst (similar to 0.025%h(-1)). TEM images before and after reaction show that the average particle size for the uncoated catalyst increases from 8.5 nm to 24.5 nm, indicating sintering, whereas the 5-ALD catalyst retained the initial particle size. The reduced particle size also explains the 50% reduction in carbon formation-rate in the 5-ALD catalyst. The developed sequential H-2-CO chemisorption technique reliably measures in-situ dispersion in uncoated and ALD coated catalysts with exposed active sites. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.