Through the impregnation method, Ag catalysts with different support (such as TiO<sub>2</sub> and γ-Al<sub>2</sub>O<sub>3</sub>) were prepared and then tested for catalytic oxidati...Through the impregnation method, Ag catalysts with different support (such as TiO<sub>2</sub> and γ-Al<sub>2</sub>O<sub>3</sub>) were prepared and then tested for catalytic oxidation of formaldehyde (HCHO) at low temperatures. The Ag/TiO<sub>2</sub> catalyst exhibited strong catalytic performance, converting HCHO to CO<sub>2</sub> and H<sub>2</sub>O at around 95°C. However, the Ag/Al<sub>2</sub>O<sub>3</sub> catalysts showed much lower activity and reached 100% conversion at 125°C. The Ag-based catalysts were next characterized by several methods (XRD, TEM, FT-R, BET and H<sub>2</sub>-TPR). Results of characterization revealed that support dramatically impacts the size and dispersion of Ag particles. The XRD analysis showed the existence of different peaks of the silver on the surface of Al<sub>2</sub>O<sub>3</sub> in the contrast with TiO<sub>2</sub> no specific peaks exist. Therefore, the size of the Ag particles and their dispersion are the most important factors that affect their catalytic performance for formaldehyde oxidation. In terms of catalytic performance for HCHO oxidation, the Ag/TiO<sub>2 </sub>catalyst possesses the best Ag dispersion, as well as the smallest Ag particle size.展开更多
Sulfonated catalysts based on zirconia (SO3</sub>H-ZrO2</sub>), silica (SO3</sub>H-SBA-15) and zeolite (SO3</sub>H-ZSM-5) were studied in the catalytic hydrolysis reaction of hemicellulose in a...Sulfonated catalysts based on zirconia (SO3</sub>H-ZrO2</sub>), silica (SO3</sub>H-SBA-15) and zeolite (SO3</sub>H-ZSM-5) were studied in the catalytic hydrolysis reaction of hemicellulose in a microwave reactor. The prepared catalysts were characterized by various techniques (XRD, N2</sub> physisorption at 77 K, SEM, TEM and NH3</sub>-TPD). The obtained results reveal that despite the differences in their structural and textural properties, the ZrO2</sub>, Al-SBA-15 and H-ZSM-5 supports show similar conversions. Doping supports with sulfonate species created hydrogen bonds between SO3</sub>H groups and increased the amount of weak acid sites, which enhanced the hydrolysis of hemicellulose. SO3</sub>H- ZSM-5 showed the highest catalytic activity followed by SO3</sub>H-SBA-15 while SO3</sub>H-ZrO2</sub> exhibited a poor conversion. Furthermore, the catalytic hydrolysis of the hemicellulose leads to several interesting products, such as formic acid, acetic acid, lactic acid and xylan. The correlation between the catalytic performances and the acidic properties of the different samples indicates that the best catalytic performances were obtained with the least acidic solids and especially when the density of strong acid sites decreases.展开更多
Aerogel Pd/(Ce0.33Zr0.66O2)SiO2 catalysts (CeZry) were prepared with variable Ce and Zr loadings (molar ratio Ce/Zr = 1/2) by combining sol-gel and impregnation methods. First, N2-physisorption was used to investigate...Aerogel Pd/(Ce0.33Zr0.66O2)SiO2 catalysts (CeZry) were prepared with variable Ce and Zr loadings (molar ratio Ce/Zr = 1/2) by combining sol-gel and impregnation methods. First, N2-physisorption was used to investigate the texture evolution. Then, H2-chimisorption and TEM were performed to study the effect on particle dispersion. After, TPR was used to determine the catalyst reducibility. Furthermore, XPS characterization was done to identify the palladium oxidation state and to evaluate the Pd-support interaction. Finally, the prepared catalysts were tested in methane combustion to assess their catalytic activity. The obtained results showed that, when the Zr and Ce loadings are varied between 0% and 8% and between 0% and 6% respectively, the BET surface area was increased from 615 to 744 m2/g, the porosity diameter from 45.7 to 83.6 Å, the Pd particle diameter from 5.2 to 7.0 nm, the CeO2 and ZrO2 particle size from 0 to 68 nm, the reduction temperature shift reached 16°C, the Pd binding energy shift attained 0.6 eV, but an optimum amounts of Zr (4 wt.%) and Ce (3 wt.%) are needed to maximize the PdO reducibility and to enhance the catalytic activity. In effect, 100% conversion of methane was reached at around 415°C on the CeZr4 catalyst.展开更多
文摘Through the impregnation method, Ag catalysts with different support (such as TiO<sub>2</sub> and γ-Al<sub>2</sub>O<sub>3</sub>) were prepared and then tested for catalytic oxidation of formaldehyde (HCHO) at low temperatures. The Ag/TiO<sub>2</sub> catalyst exhibited strong catalytic performance, converting HCHO to CO<sub>2</sub> and H<sub>2</sub>O at around 95°C. However, the Ag/Al<sub>2</sub>O<sub>3</sub> catalysts showed much lower activity and reached 100% conversion at 125°C. The Ag-based catalysts were next characterized by several methods (XRD, TEM, FT-R, BET and H<sub>2</sub>-TPR). Results of characterization revealed that support dramatically impacts the size and dispersion of Ag particles. The XRD analysis showed the existence of different peaks of the silver on the surface of Al<sub>2</sub>O<sub>3</sub> in the contrast with TiO<sub>2</sub> no specific peaks exist. Therefore, the size of the Ag particles and their dispersion are the most important factors that affect their catalytic performance for formaldehyde oxidation. In terms of catalytic performance for HCHO oxidation, the Ag/TiO<sub>2 </sub>catalyst possesses the best Ag dispersion, as well as the smallest Ag particle size.
文摘Sulfonated catalysts based on zirconia (SO3</sub>H-ZrO2</sub>), silica (SO3</sub>H-SBA-15) and zeolite (SO3</sub>H-ZSM-5) were studied in the catalytic hydrolysis reaction of hemicellulose in a microwave reactor. The prepared catalysts were characterized by various techniques (XRD, N2</sub> physisorption at 77 K, SEM, TEM and NH3</sub>-TPD). The obtained results reveal that despite the differences in their structural and textural properties, the ZrO2</sub>, Al-SBA-15 and H-ZSM-5 supports show similar conversions. Doping supports with sulfonate species created hydrogen bonds between SO3</sub>H groups and increased the amount of weak acid sites, which enhanced the hydrolysis of hemicellulose. SO3</sub>H- ZSM-5 showed the highest catalytic activity followed by SO3</sub>H-SBA-15 while SO3</sub>H-ZrO2</sub> exhibited a poor conversion. Furthermore, the catalytic hydrolysis of the hemicellulose leads to several interesting products, such as formic acid, acetic acid, lactic acid and xylan. The correlation between the catalytic performances and the acidic properties of the different samples indicates that the best catalytic performances were obtained with the least acidic solids and especially when the density of strong acid sites decreases.
文摘Aerogel Pd/(Ce0.33Zr0.66O2)SiO2 catalysts (CeZry) were prepared with variable Ce and Zr loadings (molar ratio Ce/Zr = 1/2) by combining sol-gel and impregnation methods. First, N2-physisorption was used to investigate the texture evolution. Then, H2-chimisorption and TEM were performed to study the effect on particle dispersion. After, TPR was used to determine the catalyst reducibility. Furthermore, XPS characterization was done to identify the palladium oxidation state and to evaluate the Pd-support interaction. Finally, the prepared catalysts were tested in methane combustion to assess their catalytic activity. The obtained results showed that, when the Zr and Ce loadings are varied between 0% and 8% and between 0% and 6% respectively, the BET surface area was increased from 615 to 744 m2/g, the porosity diameter from 45.7 to 83.6 Å, the Pd particle diameter from 5.2 to 7.0 nm, the CeO2 and ZrO2 particle size from 0 to 68 nm, the reduction temperature shift reached 16°C, the Pd binding energy shift attained 0.6 eV, but an optimum amounts of Zr (4 wt.%) and Ce (3 wt.%) are needed to maximize the PdO reducibility and to enhance the catalytic activity. In effect, 100% conversion of methane was reached at around 415°C on the CeZr4 catalyst.
