Stabilising alumina supported nickel particles against sintering in ammonia/hydrogen atmosphere

Abstract

Two different methods to stabilise alumina-supported nickel particles against sintering have been studied. The first investigated method was co-impregnation using precursors of nickel and different promoters (i.e. oxides of Li, Na, K, Mg, Ca, La and Ce) and the second was formation of a protecting nickel aluminate layer between the nickel particles and the γ-alumina support. The samples were heat-treated in ammonia + hydrogen at 523 K and 250 bar. The sintering process was mainly followed by hydrogen chemisorption. The samples were also characterised by specific surface area measurements, X-ray diffraction and transmission electron microscopy with energy dispersive X-ray mapping. Co-impregnation with oxides of alkali metals, alkaline earths, or lanthanides markedly suppressed the sintering of nickel. The most pronounced effect was achieved for the samples promoted with alkaline earths for which up to 50% of the active surface area remained after the heat-treatment in ammonia + hydrogen compared with the Ni/Al 2O 3 reference sample. The formation of nickel aluminate by sequential impregnation of the nickel precursors, with calcination at 923 K between the impregnations, enhanced the sintering stability with 35% compared to the reference sample.