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.

Low-Temperature Plasma-Assisted Catalytic Dry Reforming of Methane over CeO2 Nanorod-Supported NiO Catalysts in a Dielectric Barrier Discharge Reactor

“…In general, the reduction peaks of CeO 2 -supported NiO catalysts are observed in the temperature range of 200–600 °C . Thus, these high-temperature reduction peaks at 731, 745, and 756 °C for these three samples are ascribed to the bulk reduction of CeO 2 support. , The addition of NiO has a significant influence on the low-temperature surface reducibility (i.e., reduction temperature and hydrogen consumption) of CeO 2 , as shown in Figure . The low-temperature peaks (α 1 and α 2 ) observed below 250 °C were caused by the reduction of surface oxygen, which are possibly attached to the oxygen vacancies generated by the partial substitution of Ce 4+ ions with Ni 2+ ions.…”

Enhanced Low-Temperature CO2 Methanation over Bimetallic Ni–Ru Catalysts

“…This is mostly due to increased accessibility/exposure of small particles and H 2 diffusion limitations for large particles . The bimetallic 20Ni0.1Ru catalyst exhibited three H 2 consumption signals, where the peak at 83 °C corresponds to the reduction of ruthenium oxide species with the signals at 147 and 268 °C attributed to highly dispersed NiO particles and bulky NiO phase, respectively . The TPR profiles for 20Ni0.2Ru and 20Ni1.0Ru are similar.…”

“…41 The bimetallic 20Ni0.1Ru catalyst exhibited three H 2 consumption signals, where the peak at 83 °C corresponds to the reduction of ruthenium oxide species with the signals at 147 and 268 °C attributed to highly dispersed NiO particles and bulky NiO phase, respectively. 42 The TPR profiles for 20Ni0.2Ru and 20Ni1.0Ru are similar. The peak at 102 °C observed over both samples can be assigned to reduction of ruthenium oxide species, and the peaks at 256 °C can be ascribed to the reduction of surface NiO species.…”

Ni/Co in and on CeO2: a comparative study on the dry reforming reaction

“…4a). The peaks observed at low temperatures can be explained as being due to the reduction of oxygen adsorbed on the vacancies 87 caused by the incorporation of Ni 2+ within the CeO 2 . Thus, two forms of oxygen surface lattice exist and the one which is available at low temperature is generally useful in catalytic reactions.…”