(757b) Naphthalene Steam Reforming Over Ni/Ce0.75Zr0.25-XMnxO2 (x = 0, 0.10, 0.20 and 0.25) Mixed Oxide Catalysts

Abstract:

Biomass
gasification is gaining attention as a route for biomass energy production. One
of the main technical barriers in the
development of biomass gasification process is the problems due to the presence of heavy
organic impurities, especially tarry compounds, in the flue gas. Tar creates various difficulties, for example, condensation
or formation of tar aerosols, causing downstream problems in the process
equipments.

In this
study, the catalytic activity of nickel supported on Ce_0.75Zr_0.25-xMn_xO₂
(x = 0, 0.10, 0.20 and 0.25) mixed oxide catalysts prepared by urea hydrolysis
and incipient wetness impregnation was investigated via steam reforming
reaction of naphthalene as a model biomass tar compound. Experiments were
carried out in a fixed bed reactor at 700 ^oC
and atmospheric pressure using a molar ratio of steam/carbon (S/C) equal to 2. The catalysts
were characterized by various techniques, such as surface area,
temperature-programmed reduction (TPR), X-ray diffraction (XRD) and temperature-programmed
oxidation (TPO).

The catalytic
performance data showed that nickel supported on mixed oxide catalysts exhibit
high activities and stabilities for the steam reforming of naphthalene and high
resistance toward carbon deposition. The steam reforming products are mainly
CO, CO₂ and H₂ for Ni/Ce_0.75Zr_0.25-xMn_xO₂
(x = 0.10, 0.20 and 0.25) and the H₂/CO ratio is about 2.40 ± 0.12.
On the other hand, the main products of naphthalene steam reforming over Ni/Ce_0.75Zr_0.25O₂
are CO, CO₂, H₂ and trace of CH₄ and the H₂/CO
ratio is about 1.84 ±
0.05, indicating carbon formation.

The results
showed that, Mn-doped Ni/Ce_0.75Zr_0.25-xMn_xO₂
(x = 0.10, 0.20 and 0.25) catalysts yielded much lower amounts of carbon formed
(1.1 ±
0.3 mg g_cat^-1) than Ni/Ce_0.75Zr_0.25O₂
catalyst (26.7 mg g_cat^-1). It is then, suggested that the
incorporation of manganese ions into ceria lattice improved the oxygen storage
capacity as well as the oxygen mobility on the surface of mixed oxides,
facilitating gasification of surface carbon. The promotion effect of manganese
on the nickel supported on Ce_0.75Zr_0.25-xMn_xO₂
catalyst for steam reforming of naphthalene is probably through a redox
mechanism. The lower valence state manganese might adsorb water and dissociate
it, the resulting species ?O or ?OH transferring to the nickel and reacting
with surface carbon species to form carbon monoxide, carbon dioxide and
hydrogen.

Keywords: Naphthalene steam reforming,
Ceria-zirconia, Manganese.