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

Role of water in metal catalyst performance for ketone hydrogenation: a joint experimental and theoretical study on levulinic acid conversion into gamma-valerolactone

CO is a toxic and detrimental air pollutant. It not only affects human beings but also vegetation and indirectly increases global warming. An estimate has shown that vehicular exhaust contributes about 64% of the CO pollution in developed countries. Due to the exponentially increasing number of automobiles on roads, CO concentrations have reached an alarming level in urban areas and regulatory measures had been adopted to curb the menace of vehicular pollution. To control vehicular exhaust pollution, end-of-pipe-technology using noble metals catalytic converters are recommended. The increasing prices of noble metals with the increasing number of vehicles motivates the investigation of material concepts to reduce the precious metal content in automotive catalysts or to find a substitute for noble metals. Among non-noble metals, copper chromite is found to be most promising and exhibits comparable activity for CO oxidation to that of precious metals. Further, low cost, easy availability and advance synthesi...

A Review on CO Oxidation Over Copper Chromite Catalyst

Automotive Three-Way Catalysts (TWC) were introduced more than 40 years ago. Despite that, the development of a sustainable TWC still remains a critical research topic owing to the increasingly stringent emission regulations together with the price and scarcity of precious metals. Among other material classes, perovskite-type oxides are known to be valuable alternatives to conventionally used TWC compositions and have demonstrated to be suitable for a wide range of automotive applications, ranging from TWC to Diesel Oxidation Catalysts (DOC), from NOx Storage Reduction catalysts (NSR) to soot combustion catalysts. The interest in these catalysts has been revitalized in the past ten years by the introduction of the concept of catalyst regenerability of perovskite-based TWC, which is in principle well applicable to other catalytic processes as well, and by the possibility to reduce the amounts of critical elements, such as precious metals without seriously lowering the catalytic performance. The aim of this review is to show that perovskite-type oxides have the potential to fulfil the requirements (high activity, stability, and possibility to be included into structured catalysts) for implementation in TWC.

https://www.mdpi.com/2073-4344/4/3/226/pdf

Structured Perovskite-Based Catalysts and Their Application as Three-Way Catalytic Converters—A Review

Doping of LaCoO3 with copper to add reduction functionality in addition to the known oxidation properties has been investigated, aiming at three-way catalysis (TWC) applications. Nanoscale perovskites with nominal composition LaCo1−xCuxO3, (x = 0, 0.1, 0.3, and 0.5) have been synthesized by means of the citrate method. A stable perovskitic phase with rhombohedral geometry up to an unprecedented x = 0.5 has been obtained and characterized by BET, X-ray diffraction (XRD), Temperature Programmed Reduction (TPR), X-ray Photoelectron Spectroscopy (XPS), and Scanning Electron Microscopy (SEM). The crystallite size decreases with increasing the copper amount and also the morphology differs; moreover the surface reactivity with respect to atmospheric moisture and carbon dioxide is more evident in the sample with x = 0.5. Reactivity has been measured in simple NO + CO and CO + O2 model reactions, as well as with complex mixtures approaching automotive exhaust composition, at both stoichiometric and O2 limiting conditions. The catalysts have been characterized after reaction as well. The perovskite with the highest Cu amount, LaCo0.5Cu0.5O3, exhibits an interesting compromise of oxidation and NO reduction functionality at interesting, low temperatures with very short contact time (GHSV = 1,000,000 h−1). Still, activity for NO reduction in real mixtures requires substoichiometric O2.

Largely Cu-doped LaCo1−xCuxO3 perovskites for TWC: Toward new PGM-free catalysts

The catalytic activity of supported chromites MCr2O4/γ-Al2O3 (M = Cu, Co, Mn, Zn, Mg) in the oxidation of CO, C3H6, and o-xylene and NOx reduction was studied. The catalytic activity depends on the calcination temperature and cation nature. The features of the formation of the catalysts were studied by the UV-Vis diffuse reflectance and IR spectroscopies.

Catalytic properties of chromites with a spinel structure in the oxidation of CO and hydrocarbons and reduction of nitrogen oxides

The catalytic activity of perovskites MIMIIO3 (MI=La; MII=Co, Mn, Cr, Al, Ni, and V) and MICoO3 (M=Y, Nd, Sm, and Er) in the oxidation of CO, propylene, and ethylbenzene was investigated. The highest activity was observed for the MICoO3 catalysts with perfect perovskite structure. The nature of the rare-earth element has no influence on the catalytic activity. Deformation of the octahedral coordination of the metal was found for the less active catalysts. The interaction of gases (CO, CO+air) with the catalyst surface was investigated. The more active catalysts adsorb a greater amount of O2, and the adsorption occurs in the temperature region of the oxidation reaction. The activities of the perovskite- and spinel-type catalysts were compared under similar conditions.

Oxidation of CO and hydrocarbons over perovskite-type complex oxides

Catalytic oxidation of CO and hydrocarbons on SHS-prepared complex metal oxide catalysts

The catalytic activity of MIMII2O3 spinel-type complex oxides (MI = Cu, Ni, Mn, Zn, Mg, Co, MII = Co, Cr, Al) in the oxidation of CO and ethylbenzene has been investigated. The Co-containing catalysts were more active than the Cr- and Al-containing catalysts. The nature of the cation influenced the catalytic activity. Higher activities were observed for the catalysts containing two transition elements. A correlation between the catalytic and adsorption properties was established.

Catalytic properties of spinel-type complex oxides in oxidation reactions

The catalytic activity of MIMIIO3] perovskite-type complex oxides (MI = La, Y, Nd, Yb; MII = Co, Mn, Ni) in the oxidation of CO, propylene, benzene, ethylbenzene,o-xylene, and ethyl acetate was investigated. The Co-containing catalysts were shown to be more active in the oxidation than the Mn-containing catalysts. A relationship between the catalytic and adsorption properties was established.

G. N. Pirogova

Papers

Catalytic properties of chromites with a spinel structure in the oxidation of CO and hydrocarbons and reduction of nitrogen oxides

Oxidation of CO and hydrocarbons over perovskite-type complex oxides

Catalytic oxidation of CO and hydrocarbons on SHS-prepared complex metal oxide catalysts

Catalytic properties of spinel-type complex oxides in oxidation reactions

Catalytic oxidation of CO, hydrocarbons, and ethyl acetate over perovskite-type complex oxides