Laboratory Evaluation of Three-Way Catalysts

Ceria‐Based Solid Catalysts for Organic Chemistry

“…In BiCeVMoO catalysts, bismuth may be substituted by a low amount of cerium while the structure of BiVMoO remains unchanging. With the increasing of Ce (Ce/Ce+Bi > 0.15), new phases of CeVO 4 and Ce 2 (MoO 4 ) 3 formed. The cerium promotes the forming of acrolein, and the selectivity to acrolein increased to a maximum at Ce/Ce+Bi atomic ratio equal to 0.15 (45 mol % at about 30 mol % propane conversion).…”

“…The material is able to store oxygen during the lean phase (i.e., excess of oxygen) and to give oxygen back to metal particles during the rich phase (when there is virtually no O 2 in the gas phase); this is the so-called oxygen storage capacity (OSC) of ceria. The use of OSC components was first proposed by Ghandi et al in 1976. [4] Since the pioneering works of Yao and Yu Yao [2] and of Su et al, [5,6] many studies have been devoted to improving knowledge of the kinetics of OSC [7][8][9] and of the mechanisms implicated in surface and bulk oxygen mobility in ceria and related compounds, [10][11][12][13][14] with a special insight into CeZrO x oxides.…”

“…The use of OSC components was first proposed by Ghandi et al in 1976. [4] Since the pioneering works of Yao and Yu Yao [2] and of Su et al, [5,6] many studies have been devoted to improving knowledge of the kinetics of OSC [7][8][9] and of the mechanisms implicated in surface and bulk oxygen mobility in ceria and related compounds, [10][11][12][13][14] with a special insight into CeZrO x oxides. [15][16][17][18][19] Oxygen diffusivity in these materials can be measured by 18 O/ 16 O isotopic exchange, [20][21][22] while oxygen species (e.g., superoxides, peroxides) that might be involved in the diffusion process can be investigated by electron spin resonance (ESR) [23][24][25][26][27] or FTIR.…”

“…[32,33] As mentioned above, it is generally accepted that one surface oxygen atom out of four is involved in the redox process shown in Equation (2), which represents a theoretical OSC value of 5.4 mmol O m À2 for a mean surface density of 13.1 mmol O m À2 . [22,33] Reduced ceria is able to dissociate water [34][35][36][37][38] or carbon dioxide [34,36] according to Equation (4) or the reverse of Equation (2) Ceria also possesses versatile acid-base properties, depending on the nature and temperature of the pretreatment. Ceria can chemisorb pyrrole, a proton donor, and CO 2 , an electron acceptor, which is characteristic of strong Lewis-base sites.…”

Caracterização textural, morfológica e estrutural de catalisadores automotivos novos e usados

“…O envenenamento é de natureza química, a formação de fuligem é um processo mecânico e a degradação térmica (sinterização ou transformação dos metais ativos) ocorre em função da temperatura [16][17][18][19][20][21][22][23][24][25][26][27][28].…”