Mixed oxide

About: Mixed oxide is a research topic. Over the lifetime, 5224 publications have been published within this topic receiving 115567 citations.

ZnO-modified zirconia as gold catalyst support for the low-temperature methanol steam reforming reaction

Abstract: Nanoscale zirconia (ZrO 2 ) is widely investigated both as catalyst support and catalyst. Bare ZrO 2 binds gold weakly due to lack of surface defects. In this study, nanoscale ZrO 2 was modified with zinc oxide (ZnO) at different amounts, and examined as support of gold catalysts for the methanol steam reforming (SRM) reaction. ZrO 2 with high specific surface area serves as dispersant of ZnO to create highly dispersed ZnO clusters, which provide more anchoring sites for strong gold-metal oxide bonding. Addition of ZnO also passivates the surface acidity of ZrO 2 , thus blocking the direct methanol decomposition to CO and H 2 . To prepare the highly dispersed ZnO clusters on ZrO 2 , a carbon hard-template method was used, followed by calcination at 550 °C to produce a highly porous mixed oxide solid. To investigate the modification of ZrO 2 by ZnO, the surface acidity was probed with isopropanol in temperature-programmed desorption (TPD) mode. Adsorption of the gold precursor on the ZnO-modified ZrO 2 was carried out by the anion adsorption method. Better dispersion, and better activity and stability of these gold catalysts were found than on either pure ZrO 2 or ZnO. Accordingly, the light-off temperature of SRM is lower and a wider temperature window for CO-free H 2 production up to moderately high temperatures (∼375 °C) is found.

The reactivity of a Fe–Ti–O mixed oxide under different atmospheres: study of the interaction with simple alcohol molecules

Abstract: In this paper, the interaction between simple alcohols (methanol to 1-butanol) and a Fe–Ti mixed oxide was investigated. The reactivity of the mixed system was studied both at atmospheric pressure and in vacuum conditions and compared with that of the pure oxides (TiO2 and Fe2O3). To understand the influence of the oxygen presence in the reaction mixture, the reactivity was investigated both in inert gas as well as in oxygen atmosphere. X-ray photoelectron spectroscopy (XPS) and quadrupole mass spectrometry (QMS) have been used for the experiment in high vacuum (HV), while Fourier transform infrared spectroscopy (FTIR) and QMS have been used for the experiment in rough vacuum and under atmospheric pressure conditions. The characterisation of the sample by means of XPS, X-ray diffraction and IR spectroscopy preceded the reactivity study. When compared with Fe2O3, the Fe–Ti–O mixed oxide seems to be less reactive with respect to the alcohols; the interaction between alcohol and surface is mainly molecular, as in the case of TiO2. Moreover, the oxidising power of the mixed oxide is lower than that of Fe2O3 (only traces of carbonic compounds are evident).

Comparison of TiO2-based oxide catalysts for the selective catalytic reduction of NO: effect of aging the vanadium precursor solution

Abstract: The performance of several TiO 2 -based polyoxide supports loaded with vanadia was tested for the selective catalytic reduction of NO with ammonia as reductant. It is remarkable to note that the valence of vanadium in the precursor solution during the impregnation step is crucial for the synthesis of efficient DeNO x catalysts. More specifically, V 5+ in the precursor solution yields lower-performance catalysts compared to the case of V 4+ under identical conditions. Aging the vanadium precursor solution, which is associated with the reduction of V 5+ to V 4+ (VO 2 + → VO 2+ ), prior to impregnation results in catalysts with excellent catalytic behavior under identical activation and operating conditions. The present variation of loading vanadia is used for TiO 2 -based supports with low crystallinity. These supports, which have traditionally performed poorly, are now able to function as effective SCR catalysts. Increasing the acidity of the support by incorporating oxides such as WO 3 and Al 2 O 3 significantly improves the SCR activity and nitrogen selectivity. The concentration of tungsten used in these catalysts was higher than that typically used in industry. It was also found that the supports should be synthesized with the simultaneous precipitation of the corresponding precursors. From our work we found that the mixed oxide catalysts possess Bronsted and Lewis acid sites of comparable strength over a wide range of temperatures. Catalysts prepared from aged vanadium precursor solutions demonstrated a wider temperature window for optimum operation. FT-IR, NH 3 -temperature programmed desorption, XRD, and UV/VIS were used to characterize the catalysts tested in this work.