Abstract
Vacuum-drying and freeze-drying were adopted to improve the catalytic activity of Ce0.5Pr0.5O2 for soot combustion. The specific surface area and pore volume of the as-prepared Ce0.5Pr0.5O2 were greatly increased compared to the counterpart using the common drying method. Furthermore, the redox performance and the oxidation ability for soot were enhanced, as demonstrated by H2-TPR and soot-TPR. Thus, lower combustion temperatures and higher intrinsic activity were obtained. This work demonstrated that simply changing the drying process of precipitates can be served as a paradigm to improve the structure and catalytic performance.
Highlights
Soot particulates emitted from diesel engines have caused seriously deleterious effects on human health and environment (Wei et al, 2011; Lin et al, 2013; Wei et al, 2014; Fino et al, 2016; Yu et al, 2019; Tsai et al, 2020)
X-ray powder diffraction (XRD) patterns show that all the as-prepared samples are indexed to the structure of fluorite CeO2 (JCPDS 43–1002), and no other peaks were found (Figure 1), implying the formation of CePr solid solution due to the similar ionic radius of Ce4+ (0.97 Å) with Pr4+ (0.96 Å)
It is noted that the intensity of the diffraction peaks of CPO-E and CPO-F is lower than those of CPO, suggesting the lower crystallinity or more defects/vacancies for CPO-E and CPO-F, which would benefit the redox property and catalytic activity (Martínez-Munuera et al, 2019)
Summary
Soot particulates emitted from diesel engines have caused seriously deleterious effects on human health and environment (Wei et al, 2011; Lin et al, 2013; Wei et al, 2014; Fino et al, 2016; Yu et al, 2019; Tsai et al, 2020). Bueno-López et al (Bueno-Lopez et al, 2005) reported that doping of La3+ increases surface area and redox properties of CeO2, and enhances its catalytic soot combustion activity. After cooling to room temperature, the temperature was programmed in a He atmosphere under the condition of a heating rate of 5°C/min, reaching 850°C. Soot was mixed with the catalyst in an agate mortar for 30 min to obtain a homogeneous mixture. After cooling to room temperature, a gas flow with 5 vol.% O2 in He was introduced, and TPO was started at a heating rate of 5°C/min until reaching 750°C. The number of active redox sites available to soot under these reaction conditions can be quantified by integrating the diminishing rate of CO2 formation over time
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