Effect of composition of multicomponent supports on properties of supported Nickel catalysts

Abstract

Ni catalysts supported on combinations of alumina, magnesia, zirconia with rare earth supports are studied for the steam reforming of ethanol (ESR). The composition of the supports is systematically varied to identify the role of individual components and their contribution when they are combined. Supports containing magnesia or zirconia show contrasting behavior of acidity, XRD crystallite size of NiO, reducibility, dispersion of Ni(0), OSC, coking and metals sintering characteristics. Catalyst activity and deactivation are strongly influenced due to these differences. HRTEM indicates the redispersion of Ni(0) during reduction of NiO on catalysts containing magnesia. Magnesia and alumina-magnesia based catalysts show hindered reduction of nickel and highest intrinsic activity (H2 yields). But sintering of Ni is their nemesis. Moderate interaction of Ni with zirconia-based supports (H2-TPR) lends sintering stability in ESR. Quaternary Alumina-Magnesia-Zirconia catalysts imbibe advantages of individual components and are overall best with fair H2 yield, good stability and regenerability. Long duration (80 hours) performance tests give holistic results because they encompass multiple factors influencing deactivation. Intrinsic chemical reactivity (as opposed to) active metal dispersion is important while comparing the activity of catalysts with different compositions. Degree of reducibility of nickel is an important consideration while measuring metal dispersion by chemisorption. Metal reducibility by H2-TPR, dispersion measurement by chemisorption and particle size determination by HRTEM are used as complementary techniques for rationalizing results of metal dispersion measurement.