Mixed zirconia-alumina supports for Ni/MgO based catalytic filters for biomass fuel gas cleaning

Localized, small scale renewable energy generation by biomass gasification will only find widespread use if simple and efficient technology is available for removing undesired impurities such as particles and tar from the producer gas in order to avoid serious operating problems in the downstream equipment and coupled diesel engine. This work focuses on the further improvement of a novel one-step cleanup with a catalytic candle filter by using alternative ZrO2 or ZrO2-Al2O3 mixed supports in order to improve the activity of Ni-based catalysts at lower temperatures. Porous alpha-alumina filter materials were prepared with the urea method to deposit 2.5 wt.% Al2O3 or ZrO2, or a combination of ZrO2 and Al2O3 to increase the surface area, followed by 1 wt.% Ni and 0.5 wt.% MgO deposition. The surface area increases with the number of deposition cycles of ZrO2 or ZrO2-Al2O3, but was lower than for pure Al2O3 deposition. Uniform distributions of the zirconia secondary support and the active ingredients such as Ni and MgO throughout the sample could be obtained. Tar conversion achieved from the three types of supports: ZrO2, Al2O3 and a mixed ZrO2-Al2O3 are generally similar, except at high velocity and low temperature where the mixed support is best. As an example, for the mixed oxide deposit of 1.20 Wt.% ZrO2+1.28 wt.% Al2O3 followed by 0.46 wt.% MgO+0.996 wt.% Ni at 900 degrees C, 2.5 cm/s, with 15 g/Nm(3) benzene or 5 g/Nm(3) naphthalene loading in presence of 100 ppm H2S, conversions of benzene and naphthalene were 95% and 99.5% respectively, which is extremely promising, since the surface area of these new ZrO2 based materials is lower than with pure alumina and leaves room for significant improvement. Extended time testing over 170 h under the condition of 15 g/Nm(3) benzene and 5 g/Nm(3) naphthalene fed together at 900 degrees C and in presence of 100 ppm H2S, showed 99.2-99.6% benzene conversion and 100% naphthalene conversion, even at lower temperature (850 degrees C) a good activity was still achieved in comparison with our previously developed catalysts. (C) 2007 Elsevier B.V. All rights reserved.