Oxygen vacancies play an important role in the oxidation of biomass-derived alcohols and aldehydes using ceria-based catalysts. In this study, a highly oxygen vacancy-defective Pt/H-CeO 2 catalyst was synthesized by a straightforward strategy that involved the control of the addition of ascorbic acid and nitric acid. The addition of ascorbic acid, which acted as a pore-forming agent, promoted the hydrolysis, crystallization, and subsequent growth of Ce precursor salt, resulting in the synthesis of H-CeO 2 with abundant oxygen vacancy defects and a porous thin sheet-like morphology. However, the addition of nitric acid significantly inhibited the generation of oxygen vacancy defects. The obtained H-CeO 2 exhibited significantly increased oxygen vacancy content, active oxygen species, and specific surface area compared with CeO 2 with lower oxygen vacancy defects (L-CeO 2 ). These remarkable features led to enhanced catalytic activity of Pt/H-CeO 2 for the oxidation of 5-hydroxymethylfurfural (HMF) compared with Pt/L-CeO 2 . This can be mainly attributed to the enhanced adsorption and activation of O 2 molecules by abundant oxygen vacancies, allowing more active oxygen species to participate in the dehydrogenation of HMF. This work provides an example of oxygen defect engineering for ceria-based catalysts to boost the catalytic selective oxidation performance.
The supported Pt/CeO 2 catalysts are widely used for the catalytic oxidation of CO at ambient conditions. Herein, we reported a new strategy for modifying the interaction between Pt and CeO 2 support via pulsed steam treatment, which significantly optimized the catalytic performance of Pt/CeO 2 for CO oxidation. Specifically, the hollow CeO 2 nanospheres were prepared by using carbon spheres as sacrificial templates and then subjected to pulsed steam treatment at 150 °C for different times to obtain the CeO 2 -xH support (x means the time of pulsed steam treatment, min). It was found that the complete oxidation of CO can be achieved at 90 °C over the Pt/CeO 2 –50H sample, which was much lower than that (130 °C) on Pt/CeO 2 without pulsed steam treatment. The XPS and in-situ DRIFTS characterizations were conducted to reveal the high performance of the Pt/CeO 2 –50H catalyst for CO oxidation. It was found that the valence state of Pt significantly controlled by pulsed steam treatment was critical to the catalytic activity, whereby the presence of two types of active sites (Pt 0 -CO and Pt δ+ -CO) over Pt/CeO 2 –50H greatly promoted the combination of adsorbed CO and O 2 to generate CO 2 . Accordingly, this study provides a facile method to regulate the Pt valence state by pulsed steam treatment for CeO 2 support, which is critical to the CO oxidation activity.
Metal support interactions modulation is one of the effective strategies to enhance the catalytic performance. Herein, we reported that modulating metal support interactions by switching the strength (CO, H 2 , NH 3 ) and temperature (200, 300, 400 °C) of reducing gases is a facile way to improve the catalytic performance of Pt/CeO 2 for toluene oxidation . The distinct reduction treatments will stepwise enhance the reducibility, ratio of Pt 0 and oxygen vacancy concentration, which dominated the activity. The metal support interactions modulation can significantly affect toluene deep oxidation (from benzoate to formate or monodentate carbonate) via enhancing the mobility of surface/lattice oxygen and activation ability towards O 2 molecules, since the main activation sites for O 2 molecules expand from Pt 0 sites to oxygen vacancies and Pt 0 sites with temperature increasing.
Pt/CeO2 catalysts with different support shapes and prereduction temperatures were prepared and tested in the liquid-phase hydrogenation of nitrobenzene. Detailed characterizations reveal that the support shape effect of Pt/CeO2 catalysts on nitrobenzene hydrogenation originates from the exposed crystal planes on CeO2 with different reducibilities. A high-energy surface is readily reduced to generate more Ce3+ surface sites and oxygen vacancies, not only favoring the dispersion and stabilization of Pt species due to stronger metal–support interaction but also providing more adsorption sites for reactants and intermediates. Reduction treatment at high temperatures has been proved to be an effective way to improve the performance of Pt/CeO2 catalysts by providing additional Ce3+ surface sites and high H-spillover capability. The additional Ce3+ far away from Pt, derived from a high-temperature reduction, can adsorb the N-phenylhydroxylamine intermediate more effectively due to its stronger electron-donating ability and in turn promote aniline formation. It is also found that Na ions with suitable content facilitate the generation and stabilization of surface Ce3+ by charge transfer and help Pt particles to maintain a smaller size. Consequently, a 0.25 wt % Pt catalyst, supported on Na-containing CeO2 nanorods and reduced at 600 °C, displays a high level of aniline productivity of 40.8 molAN/gPt/h and excellent stability in nitrobenzene hydrogenation at room temperature. A pathway of nitrobenzene hydrogenation catalyzed by Pt/CeO2 is also proposed.
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