Ni-alumina dry reforming catalysts: Atomic layer deposition and the issue of Ni aluminate

A catalyst consisting of 2 wt% Ni supported on a commercially available transition alumina is modified using TMA-H2O ALD cycles to deposit thin alumina overcoats on the catalyst, and it is then investigated for the catalytic dry reforming of methane (DRM) at 700 degrees C. Highly dispersed Ni rapidly sinters to form bulk Ni particles on the uncoated catalyst. In contrast, deposition of an alumina overcoat by ALD significantly lowers the rate of Ni sintering, and also lowers the propensity towards carbon deposition during DRM. Additionally, it is experimentally demonstrated that the Ni aluminate (NiAl2O4 ) spinel phase is unstable under the present DRM conditions and slowly undergoes reduction to metallic Ni and Al2O3 . Slow reduction of the Ni2+ from NiAl2O4 is proposed as the origin of the large increase in DRM activity observed for the alumina-overcoated Ni catalysts.