Different Ag/CeO2 catalysts with uniform structures and diverse surface oxygen vacancy (VO-s) contents were synthesized via a modified solution combustion method. Based on the results of Raman spectroscopy, H2-TPR and isothermal soot oxidation, it was suggested that even with gaseous O2 participating in the reaction, ceria surface sites around the catalyst–soot contact points can still be reduced by soot gradually. This interfacial reduction led to the generation of extra VO-s without changing the oxygen vacancies in the bulk of CeO2. Notably, this VO-s dynamic change and the insufficient O2− regeneration/delivery further resulted in the activation and deactivation of Ag/CeO2 during reaction with soot. This means that both the existence of ceria VO-s and its dynamic change during reaction may have a crucial influence on catalyst behavior. By further exploring these activity variations, the VO-s content, catalyst–soot contact condition and extra oxygen supplier were proved to be the three most important structural factors behind the soot oxidation activity of all the ceria-based catalysts. In this sense, Ag/CeO2 catalysts with appropriate morphology and moderate initial VO-s content may exhibit good activity for soot oxidation.
The electrocarboxylation reaction is an attractive means to convert CO 2 into valuable chemicals under ambient conditions, while it still suffers from low efficiency due to the high stability of CO 2 . In this work, we report a double activation strategy for simultaneously activating CO 2 and acetophenone by silver-doped CeO 2 (Ag-CeO 2 ) nanowires, featuring as an effective electrocatalyst for electrocarboxylation of acetophenone with CO 2 . Compared to the Ag foil, Ag nanoparticles and CeO 2 nanowires, the Ag-CeO 2 nanowire catalyst allowed to reduce the onset potential difference between CO 2 and acetophenone activation, thus enabling efficient electrocarboxylation to form 2-phenyllactic acid. The Faradaic efficiency for producing 2-phenyllactic acid reached 91% at −1.8 V versus Ag/AgI. This double activation strategy of activating both CO 2 and organic substrate molecules can benefit the catalyst design to improve activities and selectivities in upgrading CO 2 fixation for higher-value electrocarboxylation.
Meisheng Zhang,Baofang Jin,Yan Liu,Wei Liu,Duan Weng,Xiaodong Wu,Shuang Liu
In this work, O 3 activation was performed at 200 °C over two types of Ag/CeO 2 catalysts with nanocube- and nanorod-like morphologies, respectively. The O 3 -indcued surface O x − species (“O x − injection”) accelerated soot combustion over both catalysts temporarily. In contrast, the depletion of CeO 2 surface oxygen vacancies (Ce 3+ -V O-s ) caused by ozonization conferred to long-term activation. Specifically, the ozonized nanocubic Ag/CeO 2 with low initial Ce 3+ content not only benefited more from the “O x − injection”, but also exhibited good redox stability and high practical potential. Therefore, the combination of this catalyst with O 3 activation may result in efficient soot elimination in the particulate filters of vehicles.
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