(701e) Investigation into the Superior Coking Resistance of ALD-Coated, Nickel-Based Reforming Catalysts

Traditional supported-Nickel catalysts, although common, are known to be inadequate for harsh natural gas reforming conditions, especially in the Dry Reforming of Methane (DRM). This is primarily due to sintering and carbon deposition, or coking, resulting in rapid catalyst deactivation. Several approaches to improving Ni-based catalyst stability have been pursued over the years with varying degrees of success. This paper evaluates a novel catalyst prepared by the Atomic Layer Deposition (ALD) technique. A nanometer-thick over-layer of amorphous alumina is deposited via ALD on conventional wet impregnation-prepared 4% (nominal) Ni/Al2O3 catalyst with the purpose of protecting the underlying active Nickel sites from sintering, as well as inhibiting coke formation tendencies at an atomic level. Several types of reference Nickel catalysts are prepared with different supports (alumina, silica, titania) and compared to the ALD coated catalyst. Methane decomposition is widely accepted as the main mechanism of carbon precursor formation in DRM at higher temperatures. Therefore, the catalysts are evaluated by performing methane cracking reaction to facilitate rapid coking. Catalyst testing is performed in a custom TGA-DSC system with the evolved gases being monitored via an on-line MS. The data generated is correlated with data from DRIFTS studies to elucidate possible coke formation pathways. Preliminary results of carbon deposition studies showcase the superior coking resistance of the ALD catalyst as opposed to conventional ones. Investigations into the removal of coke using CO2 as an oxidant are also carried out. Detailed SEM, HR-TEM, XPS and XRD analysis provides further insight into the mechanism of coke formation and the effect of the ALD overcoat on catalyst performance. Since DRM is being promoted globally as an effective CO2 utilization pathway in gas processing (via ultra-clean fuels (Fischer-Tropsch) and value-added chemicals), there is significant merit in the application of ALD to synthesize reforming catalysts with tunable activities and stabilities.