Oxidation into CO2 is a major solution to CO abatement in air depollution treatments. The development of catalytic converters led to an extraordinary high number of publications on metal catalysts during the last fifty years. Due to the increasing price of noble metals and to remarkable progresses in oxide syntheses, catalytic oxidation of carbon monoxide over oxide catalysts has recently gained in interest, even if some oxides are known to present remarkable activity since the beginning of the 20th century. In this Review, the kinetics and mechanism of CO oxidation on single and mixed oxides are examined, alongside the catalyst structures

Catalytic Oxidation of Carbon Monoxide over Transition Metal Oxides

Perovskites as substitutes of noble metals for heterogeneous catalysis: dream or reality.

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Reactivity of Surface Species in Heterogeneous Catalysts Probed by In Situ X-ray Absorption Techniques

There is a need to reduce the use of noble metal elements—especially in the field of catalysis, where noble metals are ubiquitously applied. To this end, perovskite oxides, an important class of mixed oxide, have been attracting increasing attention for decades as potential replacements. Benefiting from the extraordinary tunability of their compositions and structures, perovskite oxides can be rationally tailored and equipped with targeted physical and chemical properties—for example, redox behavior, oxygen mobility, and ionic conductivity—for enhanced catalysis. Recently, the development of highly efficient perovskite oxide catalysts has been extensively studied. This perspective article summarizes the recent development of lanthanum-based perovskite oxides as advanced catalysts for both energy conversion applications and traditional heterogeneous reactions.

Recent Advances of Lanthanum-Based Perovskite Oxides for Catalysis

A series of Mn–M′/TiO2 (M′ = Cr, Fe, Co, Ni, Cu, Zn, Ce, and Zr) catalysts were prepared using incipient wetness technique and investigated for the low-temperature selective catalytic reduction (SCR) of NO with ammonia in the presence of excess oxygen. A combination of various physico-chemical techniques was used to investigate the influence of co-doped metals on the characteristics of Mn/TiO2 catalyst. The catalytic performance of these materials was compared with respect to the M′/Mn atomic ratio in order to examine the correlation between physicochemical characteristics and reactivity of optimized materials. XRD results suggest that metal oxide species exist in a highly dispersed state at a certain level called two-dimensional monolayer coverage. Our XPS results illustrated that the MnO2 phase is extremely dominant over the Mn2O3 phase (Mn4+/Mn3+ = 22.31, 96%) in the Mn–Ni(0.4)/TiO2 anatase catalyst, whereas Mn2O3 phase is in competition with MnO2 in other catalysts (Mn4+/Mn3+ = 1.34–12.67). H2-TPR data results are in good accordance with XPS results that the absence of the high-temperature (736 K) peak indicates that the dominant phase is MnO2 in Mn–Ni(0.4)/TiO2 catalyst. This increase in reducibility of manganese and dominant MnO2 phase seems to be the reason for the superior activity and time on stream patterns of our best catalyst. BET and pore volume measurements revealed high surface area and pore volume of the Mn–Ni/TiO2 catalyst. The in situ NH3-FTIR results suggest that the manganese (Mn/TiO2) and manganese–nickel (Mn–Ni/TiO2) surface sites have only Lewis acidity, with no apparent Bronsted acidity. The catalytic performance of various Mn–M′/TiO2 (M′/Mn = 0, 0.2, 0.4, 0.6, 0.8) catalysts was studied for the low-temperature SCR reaction at a range of temperatures (160–240 °C) under industrial conditions using GHSV = 50,000 h−1. The intrinsic activity of Mn–Ni/TiO2 catalyst with M′/Mn = 0.4 atomic ratio measured under differential reaction conditions, was found to be highly active, selective and broadening the temperature window for this reaction.

Co-doping a metal (Cr, Fe, Co, Ni, Cu, Zn, Ce, and Zr) on Mn/TiO2 catalyst and its effect on the selective reduction of NO with NH3 at low-temperatures

Methane Combustion and CO Oxidation on Zirconia-Supported La, Mn Oxides and LaMnO3 Perovskite

Zirconia supported tungsten oxide catalysts (tungsten content up to 337 wt%) were prepared by equilibrium adsorption and impregnation in acid (pH 27) and basic (pH 10) conditions using hydrous zirconium oxide After thermal treatment at 1073 K in air, the catalysts were characterized by surface area determination, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), diffuse optical reflectance, Raman spectroscopy and chemical analysis The results show that tungsten is present as a dispersed phase and as monoclinic WO3 crystallites The density of tungsten in a dispersed form was estimated as about 5 atoms nm−2 Leaching treatments with ammonia revealed that only a fraction of the dispersed tungsten interacts directly with the support surface The interacting species, in the form of small clusters, as revealed by EXAFS and Raman spectroscopy, control the ZrO2 surface area and are responsible for the structural changes in the support Subsequent thermal treatment up to 1073 K in air leaves them unchanged

WOx/ZrO2 catalysts: Part 1. Preparation, bulk and surface characterization☆

The nature of the Co (or Ni) and Mo sulfided species obtained starting from γ-Al 2 O 3 -supported Anderson heteropolyoxomolybdates (CoMo 6 and NiMo 6 ) has been analyzed by means of the extended X-ray absorption fine structure (EXAFS) technique with the aid of temperature-programmed reduction (TPR) and spectroscopic measurements. Results are discussed in relation to the adsorption isotherms and to the catalytic activity for the thiophene hydrodesulfurization (HDS) reaction. A comparison with traditional catalysts has been made.

Anderson-type heteropolyoxomolybdates in catalysis: 2. EXAFS study on γ-Al2O3-supported Mo, Co and Ni sulfided phases as HDS catalysts

ZrO2-supported La, Fe containing catalysts were prepared by impregnation of tetragonal ZrO2 with citrate-type precursors and calcination at 1073 K. The catalysts were characterized by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS) and BET specific surface area (SA) determination. The catalytic activity towards CO oxidation was tested in the range 400–900 K. XRD revealed the presence of tetragonal zirconia with traces of the monoclinic phase. LaFeO3 perovskite was detected for La, Fe loading higher than 6%. XAS suggested that LaFeO3 was formed at lower loading too. The catalytic investigation evidenced that the presence of Fe is necessary for making highly active catalysts, whose performance improves with increasing the iron content.

XAS characterization and CO oxidation on zirconia-supported LaFeO3 perovskite

ZrO2-supported La, Co oxide catalysts with different La, Co loading (2, 6, 8, 12 and 16 wt.% as LaCoO3) were prepared by impregnation of tetragonal ZrO2 with equimolar amounts of La and Co citrate precursors and calcination at 1073 K. The catalysts were characterized by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and BET specific surface area determination. Catalytic CO oxidation was performed at 298–800 K. XRD revealed the presence of tetragonal zirconia with traces of the monoclinic phase. LaCoO3 perovskite was also detected for loading higher than 6%. XAS experiments suggested that at high loading LaCoO3 and Co3O4 were formed, while at low loading, La, Co oxide species interacting with support, and hard to be structurally defined, prevailed. The catalysis study evidenced that the catalytic activity was due to segregated and highly dispersed cobalt oxide species.

S. Colonna

Papers

Methane Combustion and CO Oxidation on Zirconia-Supported La, Mn Oxides and LaMnO3 Perovskite

WOx/ZrO2 catalysts: Part 1. Preparation, bulk and surface characterization☆

Anderson-type heteropolyoxomolybdates in catalysis: 2. EXAFS study on γ-Al2O3-supported Mo, Co and Ni sulfided phases as HDS catalysts

XAS characterization and CO oxidation on zirconia-supported LaFeO3 perovskite

Zirconia supported La, Co oxides and LaCoO3 perovskite: structural characterization and catalytic CO oxidation