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Catalytic Soot Oxidation Activity of NiO-CeO2 Catalysts Prepared by a Coprecipitation Method: Influence of the Preparation pH on the Catalytic Performance.

ABSTRACT: A series of NiO-CeO2 mixed oxide catalysts have been synthesized by a modified coprecipitation method at three different pH values (pH = 8, 9, and 10). The NiO-CeO2 mixed oxide samples were characterized by TGA, XRD, inductively coupled plasma atomic emission spectroscopy (ICP-AES), FTIR, Brunauer-Emmett-Teller (BET) surface area, H2 temperature-programmed reduction (H2-TPR), and electron microscopy (high-angle annular dark-field transmission electron microscopy/energy-dispersive X-ray spectroscopy (HAADF-TEM/EDS)). The catalytic activities of the samples for soot oxidation were investigated under loose and tight contact conditions. The catalysts exhibited a high BET surface area with average crystal sizes that varied with the pH values. Electron microscopy results showed the formation of small crystallites (~5 nm) of CeO2 supported on large plate-shaped particles of NiO (~20 nm thick). XRD showed that a proportion of the Ni2+ was incorporated into the ceria network, and it appeared that the amount on Ni2+ that replaced Ce4+ was higher when the synthesis of the mixed oxides was carried out at a lower pH. Among the synthesized catalysts, Ni-Ce-8 (pH = 8) exhibited the best catalytic performance.

SUBMITTER: Bendieb Aberkane A

PROVIDER: S-EPMC6829405 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature

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Project description:In this paper, the ultrasonic-assisted desilication technique was reported as an attractive and efficient way for the preparation of hierarchical zeolites with MFI structure type. The prepared materials were used as active catalysts for the dehydration of ethanol into diethyl ether and ethylene. For all catalysts, the selectivity to diethyl ether was ca 95% or higher up to 210 °C, with catalytic activity in the range of 40-68%. In case of desilicated zeolites, at 270-290 °C, the conversion of ethanol was full with selectivity to ethylene ca 80%. MFI-type commercial zeolite was treated with a sodium and/or tetrabutylammonium hydroxide aqueous solutions (NaOH or NaOH/TBAOH) for 30 min. In the case of the application of ultrasounds, a QSonica Q700 sonicator (60 W and 20 kHz) equipped with a "1" diameter horn was used. In all cases, desilication was performed in an ice bath in order to keep the procedure conditions at low temperature. It was indicated that the use of ultrasounds during desilication procedure caused higher extraction of silicon and aluminum, which was connected with an elevated mesoporosity in relation to the samples modified in the absence of ultrasounds. Ultrasonic-assisted treatment of MFI-type zeolite caused also an apparent formation of numerous holes inside zeolite grains, resembling the look of "swiss cheese". Furthermore, it was indicated that the samples prepared using ultrasonic irradiation exhibited enhanced catalytic properties in the dehydration of ethanol. For instance, MFI-type zeolite treated with NaOH/TBAOH alkaline mixture containing 10 mol% of TBAOH in the presence of ultrasounds (M-10 s) demonstrated higher both conversion of ethanol (59% vs. 47%) and selectivity to diethyl ether (95% vs. 93%) in comparison with zeolite modified conventionally (M-10c). The best catalyst was zeolite ultrasonically desilicated with NaOH/TBAOH solution of 70 mol% of TBAOH (M-70s). Generally, this catalyst indicated the highest conversion of ethanol, very high selectivity to diethyl ether (94-100%) at 150-210 °C and the highest selectivity to ethylene among investigated catalysts (21%, 66% and 84%) at 230 °C, 250 oC and 270 °C.

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Catalytic Soot Oxidation Activity of NiO-CeO2 Catalysts Prepared by a Coprecipitation Method: Influence of the Preparation pH on the Catalytic Performance.

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