Catalisadores de Fe2O3, NiO e Fe2O3 - NiO Suportados in situ em Ce0,5Zr0,5O2 e Ce0,2Zr0,8O2 – Avaliação na Redução de NO com CO
Abstract
The increasing use of fossil fuels in combustion enginees and power generation plants
has caused a large increase in the emission of sulfur oxides, nitrogen oxides (NOx)
and carbon monoxide into the atmosphere which creates serious environmental
problems. Catalytic processes are used in the abatement of NOx and a promising
alternative is the reduction of NOx using CO as reducing agent on catalysts containing
supported transition metal oxides. Taking this into account, the aim of this study was
to prepare catalysts based on Fe2O3, NiO or Fe2O3-NiO supported on ceria-zirconia
(molar ratios Ce:Zr equal to 1:1 and 1:4), incorporating the metal precursor salt in the
sun of the support (in situ addition). The results of XRD data, Rietveld refinement and
TEM indicated the formation of a solid solution CeO2-ZrO2 with cubic structure fluorite
type; furthermore, it was not observed diffraction peaks of intense X-ray of Fe or Ni
oxide as a consequence of a proper distribution of these oxides in the supports. The
addition of Fe2O3 and/or NiO led to a decrease of the average crystallite size, causing
an increase in SBET of the catalysts compared to the pure support. N2 physisorption
measurements showed that the catalysts showed significant mesoporosity, which was
attributed to the addition of Tween 80 during the sol-gel preparation, moreover, RTPH2
results confirm that the Fe2O3 reduction occurs at lower temperatures in the
presence NiO. In addition, the catalysts showed satisfactory performance in the
reduction of NO to N2 with CO, suggesting that the sol-gel method is adequate in their
preparation. Furthermore, the catalyst 0,90Fe - 1Ce:1Zr reached the highest values of
CO conversion to CO2 and NO to N2 at lower temperatures. The Fe2O3 catalysts were
more selective to N2 formation compared to those containing NiO. In conclusion, the
conversion NO to N2 was significantly affected when in contact with O2 and H2O
interferences; however, this conversion did not change significantly in the presence of
SO2. The catalysts showed a more significant reduction in conversion of NO to N2 when
evaluated in the simultaneous presence of O2, SO2 and H2O.