ALD-coated Ni:CZA (ceria-zirconia-alumina mixed oxide) was prepared using Al2O3, TiO2 and MgO ALD to create highly stable catalysts with a non-reducible/reducible hierarchical core-shell structure. The syntheses produce an initially highly controlled shell layer, which can be modified by changing the ALD precursor and number of cycles. Dry reforming of methane (DRM) catalytic activity, selectivity, and stability of different ALD-coated samples were compared to uncoated counterparts. Before any long-term catalytic testing, samples were screened by rapid thermogravimetric analysis (DSC/TGA). Shell layer thickness was varied to determine the optimum thickness for high stability, selectivity, and activity. Long-term, high conversion packed bed reactor experiments were used to further assess the effects of the ALD overlayer. The optimal catalyst was highly stable for &gt;140 h and produced syngas close to 1:1 H2:CO ratio. Pre-DRM characterizations consisting of X-ray diffraction (XRD), porosimetry, and X-ray absorption spectroscopy (XANES and XAFS) were performed to understand the structural and electronic states in the initial catalysts. Post-run characterizations used the same methods to study changes in catalyst structure upon reaction. It was found through analysis of STEM and XAS results that optimally-prepared ALD layer catalysts were characterized by reduced coking rates, less agglomeration of Ni clusters, and more oxide-dispersed (Ni2+) sites.

Selectivities and stabilities of hierarchical catalysts prepared by atomic layer deposition (ALD) and allied techniques, for methane dry reforming

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