Abstract
We established a continuous catalytic reaction activity test system for the metal/metal oxide nanocatalysts. Firstly, the CO oxidation catalyzed by the CuO nanoparticles is chosen as the model reaction. The gas chromatography was used as the downstream detector to analyze the compositions of gases before and after the reaction. In addition, we developed a customized hydrogen temperature-programmed reduction system (TPR) for evaluating the oxidation-reduction ability of the CuO nanocatalysts. Orthogonally, scanning electron microscopy (SEM) was employed to provide the particle imagery and the particle size of the CuO nanoparticles. Experimental results showed that the initial reduction temperature of the gas-phase controlled synthesis of copper oxides-based was lower than the commercial CuO and the impregnation CuO. The decrease in the required initial reduction temperature of CuO resulted in the decrease in the required light-off temperature and also the increase in the catalytic ability to the CO oxidation. The results confirmed that the predicted performance by the TPR analysis was consistent with the measured catalytic activity. In comparison to the CuO-only single-component nanocatalysts, we also investigated the performance of hybrid nanocatalysts, using CeO2 as the support of CuO. Results showed that the additions of CeO2 effectively enhanced the oxidation-reduction ability and activity for the existing CuO-based nanocatalysts for CO oxidation. In the second section, we reported a systematic study of gas-phase controlled synthesis of copper oxides-based hybrid nanoparticles for catalytic methane combustion. SEM, DMA, and XRD were employed to provide the particle imagery and the crystallinity of nanoparticles respectively. A CH4-based temperature-programmed reduction system was developed to correlate the reducibility of nanoparticle with the catalytic performance of CH4 oxidation over various oxidation state of copper-based nanoparticle. The results showed that the CuO-NP exhibit the highest activity and the reducibility among the three single component Cu-based nanoparticle (CuO, Cu2O, Cu). In comparison to the CuO single-component nanocatalysts, CuCeOx-NP-0.83 was found to have a much lower light-off temperature (340 °C) and a higher conversion ratio, indicating that the effect of Cu-Ce interfacial metal-support interaction enhanced the catalyst activity of methane combustion. In order to analyze the activity and stability mechanism of methane combustion, the catalyst stability test was performed under oxygen-rich and oxygen-lean conditions. Under the oxygen-lean condition, the decreasing catalytic activity of CuO-NP was affected by the coking and reduction of CuO. CuCeOx-NP remained its catalytic activity under both the oxygen-lean and oxygen-rich conditions. The results showed that adding CeO2 improved the carbon oxidative reaction which substantially avoided the poisoning by coking. Furthermore, CuCeOx-NP maintained its oxidation state to prevent the irreversible reduction under the oxygen-lean condition. Our results showed that CuCeOx-NP had not only a catalytic activity, but also a high stability, which can be used to enhance efficiency of methane combustion and reduce environmental pollution for alternative energy applications.