Abstract
Atomic layer deposition (ALD) is gaining attention as a catalyst preparation method able to produce metal (oxide, sulphide, etc.) nanoparticles of uniform size down to single atoms. This work reports our initial experiments to support nickel on mesoporous zirconia. Nickel (2,2,6,6-tetramethyl-3,5-heptanedionate)2 [Ni(thd)2] was reacted in a fixed-bed ALD reactor with zirconia, characterised with BET surface area of 72 m2/g and mean pore size of 14 nm. According to X-ray fluorescence measurements, the average nickel loading on the top part of the support bed was on the order of 1 wt%, corresponding to circa one nickel atom per square nanometre. Cross-sectional scanning electron microscopy combined with energy-dispersive spectroscopy confirmed that in the top part of the fixed support bed, nickel was distributed throughout the zirconia particles. X-ray photoelectron spectroscopy indicated the nickel oxidation state to be two. Organic thd ligands remained complete on the surface after the Ni(thd)2 reaction with zirconia, as followed with diffuse reflectance infrared Fourier transform spectroscopy. The ligands could be fully removed by oxidation at 400 °C. These initial results indicate that nickel catalysts on zirconia can likely be made by ALD. Before catalytic testing, in addition to increasing the nickel loading by repeated ALD cycles, optimization of the process parameters is required to ensure uniform distribution of nickel throughout the support bed and within the zirconia particles.
Highlights
Atomic layer deposition (ALD) is a thin film growth method that allows the preparation of uniform inorganic material layers on arbitrarily complex three-dimensional structures
The Ni(thd)2 was evaporated at approximately 140 °C and led through a fixed bed of mesoporous zirconia stabilised at 200 °C
For ALD, where saturation of the surface with adsorbed species has taken place throughout, a constant nickel concentration would be expected throughout the support bed
Summary
Atomic layer deposition (ALD) is a thin film growth method that allows the preparation of uniform inorganic material layers on arbitrarily complex three-dimensional structures. ALD can coat conformally porous high-surface-area catalyst supports by catalytically active materials. The first reports of the use of ALD for preparing supported heterogeneous catalysts are from the Soviet Union in the early 1970s, typically reported under the name “molecular layering” [12, 19,20,21,22,23,24]. Interest in ALD for the preparation of supported heterogeneous catalysts has again been increasing during the past decade [33,34,35,36,37,38,39].
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