Thermally-activated Al(OH)3: phase transformations and porosity

Thermochemically activated aluminum trihydroxide (Al (OH)3) is an important intermediate for ceramics, construction materials, catalysts, etc. Functional properties of materials based on Al (OH)3 depend on its phase composition and porosity. A series of thermochemically activated Al (OH)3 calcined at temperatures from 120 to 800 °C were studied by low-temperature N2 sorption, XRD and thermal analysis. It was shown that transformation of gibbsite to boehmite occurs below 300 °C and is accompanied by increasing of specific surface area and pore volume. Transformation of boehmite to γ-Al2O3 proceeds above 400 °C. The sample calcined at 500 °C was shown to consist of monophase γ-Al2O3 with specific surface area of 206 m2/g and pore volume of 0.55 cm3/g

Thermally-activated Al(OH)3: phase transformations and porosity

Thermochemically activated aluminum trihydroxide (Al (OH)3) is an important intermediate for ceramics, construction materials, catalysts, etc. Functional properties of materials based on Al (OH)3 depend on its phase composition and porosity. A series of thermochemically activated Al (OH)3 calcined at temperatures from 120 to 800 °C were studied by low-temperature N2 sorption, XRD and thermal analysis. It was shown that transformation of gibbsite to boehmite occurs below 300 °C and is accompanied by increasing of specific surface area and pore volume. Transformation of boehmite to γ-Al2O3 proceeds above 400 °C. The sample calcined at 500 °C was shown to consist of monophase γ-Al2O3 with specific surface area of 206 m2/g and pore volume of 0.55 cm3/g

Low-temperature CO oxidation over Ag/SiO2 catalysts: Effect of OH/Ag ratio

Combined application of TPx methods, H2‐O2 titration, UV–vis DRS, TGA‐DSC‐MS, TEM, XRD, N2 adsorption at −196 oC allowed proving the OH/Ag molar ratio as the key parameter defining the catalytic properties of silica-supported silver (Ag/SiO2) in low‐temperature CO oxidation. A new insight into the formation of active species on the catalyst surface is presented. In this study, Ag/SiO2 catalysts with Ag loading of 5 and 8 wt.% were prepared by incipient wetness impregnation method on the basis of commercial silicas preliminary calcined at 500, 700 and 900 °C. Detailed characterization of catalysts by physicochemical methods revealed that molar ratio between the concentration of surface OH groups (normalized to support mass) and silver amount in the prepared catalysts (OH/Ag ratio) affects the silver dispersion, structure of silver nanoparticles (NPs) and their catalytic properties. Only at optimal value of OH/Ag ratio the silver NPs are stated to possess both high dispersion and defective multidomain structure (that consists of several nanodomains) providing the adsorption of weakly bound oxygen species responsible for high catalytic activity in CO oxidation at low‐temperature. Additionally, the co-existence of two types of active sites reacting with CO at room temperature with and without formation of adsorbed carbonate species is discussed. The first type of active sites was catalytically active in low-temperature CO oxidation with CO2 release at room temperature (RT). The second type may retain surface carbonate species up to ∼40–50 °C. The balance between these species shifts towards the first type for the active catalyst

Low-temperature CO oxidation over Ag/SiO2 catalysts: Effect of OH/Ag ratio

Combined application of TPx methods, H2‐O2 titration, UV–vis DRS, TGA‐DSC‐MS, TEM, XRD, N2 adsorption at −196 oC allowed proving the OH/Ag molar ratio as the key parameter defining the catalytic properties of silica-supported silver (Ag/SiO2) in low‐temperature CO oxidation. A new insight into the formation of active species on the catalyst surface is presented. In this study, Ag/SiO2 catalysts with Ag loading of 5 and 8 wt.% were prepared by incipient wetness impregnation method on the basis of commercial silicas preliminary calcined at 500, 700 and 900 °C. Detailed characterization of catalysts by physicochemical methods revealed that molar ratio between the concentration of surface OH groups (normalized to support mass) and silver amount in the prepared catalysts (OH/Ag ratio) affects the silver dispersion, structure of silver nanoparticles (NPs) and their catalytic properties. Only at optimal value of OH/Ag ratio the silver NPs are stated to possess both high dispersion and defective multidomain structure (that consists of several nanodomains) providing the adsorption of weakly bound oxygen species responsible for high catalytic activity in CO oxidation at low‐temperature. Additionally, the co-existence of two types of active sites reacting with CO at room temperature with and without formation of adsorbed carbonate species is discussed. The first type of active sites was catalytically active in low-temperature CO oxidation with CO2 release at room temperature (RT). The second type may retain surface carbonate species up to ∼40–50 °C. The balance between these species shifts towards the first type for the active catalyst