Fluidized-bed plasma enhanced atomic layer deposition of Pd catalyst for low-temperature CO oxidation

A fluidized-bed plasma-enhanced atomic layer deposition (FP-ALD) process is reported to fabricate Pd nanoparticles using palladium hexafluoroacetylacetonate and H2 plasma. The process successfully deposits Pd nanoparticles over porous γ-Al2O3 (30 wt. %), amorphous aluminum silicate (50 wt. %), and molecular sieve (20 wt. %) (ASM) powders. Pd loading on ASM is increased linearly with increasing the number of FP-ALD cycle with a growth rate of 0.34 mg/1 g ASM/cycle. Transmission electron microscopy reveals that high-density Pd nanoparticles are uniformly distributed over the entire ASM powders and the average Pd particle size is sensitive to the number of FP-ALD cycle. By increasing the number of FP-ALD cycles from 25 to 150, the average Pd particle size rises from 0.9 to 5.8 nm, indicating the particle size can be tuned easily by varying the number of FP-ALD cycles. The catalytic activities of different particle sizes and Pd loading samples are evaluated for CO oxidation. With the metal loading amount of 2% for Pd and the average particle size of 2.9 nm, the deposited Pd/ASM sample shows an excellent catalytic activity for the oxidation of CO. Under the condition of a gas mixture of 0.5 vol. % CO and 21 vol. % O2 balanced with N2, and gas hourly space velocity of 24 000 h−1, 100% CO conversion temperature is as low as 140 °C.