The Effect of Atomic Layer Deposited Overcoat on Co-Pt-Si/γ-Al2O3 Fischer–Tropsch Catalyst

Atomic layer deposition (ALD) was used to prepare a thin alumina layer on Fischer–Tropsch catalysts. Co-Pt-Si/γ-Al2O3 catalyst was overcoated with 15–40 cycles of Al2O3 deposited from trimethylaluminum (TMA) and water vapor, followed by thermal annealing. The resulting tailored Fischer–Tropsch catalyst with 35 cycle ALD overcoating had increased activity compared to unmodified catalyst. The increase in activity was achieved without significant loss of selectivity towards heavier hydrocarbons. Altered catalyst properties were assumed to result from cobalt particle stabilization by ALD alumina overcoating and nanoscale porosity of the overcoating. In addition to optimal thickness of the overcoat, thermal annealing was an essential part of preparing ALD overcoated catalyst.