Sintering of alumina-supported nickel particles under amination conditions: Support effects

The sintering of alumina-supported nickel particles has been studied after heat-treatment in ammonia + hydrogen at 523 K and 250 bar. The investigated samples were nickel supported on γ-alumina, transalumina and α-alumina, and co-precipitated nickel oxide-alumina. The sintering process was mainly followed by hydrogen chemisorption. The samples were also characterised by specific surface area measurements, X-ray diffraction, temperature programmed desorption of ammonia, in situ FTIR spectroscopy and temperature programmed reduction. For nickel supported on γ-alumina, up to 40% of the initial metal surface area remained after the heat-treatment in ammonia + hydrogen compared with α-alumina or transalumina where only 10–20% of the initial metal surface area remained after the heat-treatment. The sintering can be correlated to the bond strength between the metal particle and the support. The larger the number of low-coordinated surface aluminium sites is, as for γ-alumina, the stronger the metal–support interaction is and this in turn suppresses diffusion of nickel particles and/or atoms.

The sintering of alumina-supported nickel particles has been studied after heat-treatment in ammonia + hydrogen. The stability of nickel against sintering can be significantly enhanced by choosing a support with strong Lewis acid sites, like γ-alumina, which can anchor the nickel particles to the support. These strong Lewis acid sites are most likely low-coordinated surface aluminium sites.Figure optionsDownload as PowerPoint slide